Loading...
HomeMy WebLinkAboutSWP272058 lai� f ® � DDDDS ENGINEERS, INC. CIVIL ENGINEERING SURVEYING PLANNING Ms. Kayren Kittrick February 2, 1996 Public Works Department DEI Project No. 95054 City of Renton 200 Mill Avenue South Renton, WA 98055 Subject: The Orchards, Sectors E, F and G Detention Calculations Dear Kayren: Enclosed are portions of the original overall storm drainage calculations for the Orchards site. Included in these calculations are the areas of Sectors E/F and G. The current development proposed on these parcels differs in concept from the original design, so I have prepared this comparison between the original and proposed land uses. As you are aware, the detention volume required is directly related to the amount of impervious area on a site. In order to verify that the design volumes in the original design are adequate for the modified land use now proposed, I have calculated the amount of impervious area to show that there is not an increase which would necessitate adding more storage volume. The original calculations assumed a tributary basin of 23.3 acres which included all of sectors E/F and G, as well as part of sector C and N.E. 6th Street. The total impervious area was 10.4 acres. The new layout for sectors E/F has an impervious area of 4.0 acres and Sector G has 3.5 acres. The portions of sector C and N.E. 6th Street that are part of the original basin 'Y' account for 2.8 acres impervious. This is a proposed total of 10.3 acres, which is slightly less than the design acreage of 10.4. Since the proposed developments are hydrologically comparable to the design basin, the detention facility, as designed, will be adequate. If you have any questions or comments please call Ed Jones or me at 885-7877. Sincerely, SHA1E 6 REC'EIVED DODDS ENGINEERS, INC. o F Ast �- �, w 2 1996 UE VCPN of n a pLANlilllVG 5 ENrCN Gary R.ASOharnbroich, P.E. �SSIONAL Project Engineer/Associate EXPIRES 12/28/ q7 Z•z 9(� 4205 1 48TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 (206) 885-7877 FAX: (206) 885-7963 DDDDS ENGINEERS, INC. C I V I L E N G I N E E RING S U R V E Y I N G R L A N N I N G STORM. DRAINAGE CALCULATIONS OR THE ORCHARDS Prepared By: Gary IZ, Shstnibroicli, P.17 A Approved By: EcIlgarl'. imics, ];.I,' v D.E.I. Project No. 88008 Date: April 4, 1994 EXPIRES 12 i 289 415 4205 148TH AVE. N.E., SUITE 200-BELLEVUE, WA 98007 [206] EIB5-71377 OR 454-3743 FAX:[206]13135-7963 TABLE OF CONTENTS A. TECHNICAL INFORMATION REPORT B. PROJECT OVERVIEW C. ONSITE DRAINAGE FEATURES 1. Existing 2. Proposed D. CORE AND SPECIAL REQUIREMENTS 1. CR#1 - Discharge at the Natural Location 2. CR#2 - Off-site Analysis 3. CR#3 - Runoff Control 4. CR#4 - Conveyance System 5. CR#5 - Erosion / Sedimentation Control Plan 6. CR#6 - Maintenance and Operation 7. CR#7 - Bonds and Liability 8. SR#1 - Critical Drainage Areas 9. SR#2 - Existing Master Drainage Plan 10. SR#3 - Master Drainage Plan 11. SR#4 - Basin and Community Plans 12. SR#5 - Special Water Quality Controls 13. SR#6 - Coalescing Plate Oil/Water Separators 14. SR#7 - Closed Depressions 15. SR#8 - Use of Lakes,Wetlands or Closed Depressions for Peak Runoff Quantity Control 16. SR#9 - Delineation of the 100 Year Floodplain 17. SR#10 - Flood Protection Facilities for the Type 1 and 2 Streams 18. SR#11 - Geotechnical Analysis and Report 19. SR#12 - Soils Analysis and Report E. ONSITE DETENTION CALCULATIONS 1. Preliminary Routing Summary 2. Existing Site Hydrology a. West Basin b. East Basin 3. Existing Upstream Mite Hydrology a. West Basin b. East Basin 4. Developed Site Hydrology a. West Basin b. East Basin 5. Hydrology Analysis a. West Basin b. East Basin F. BIOFILTRATION DESIGN CALCULATION 1. Biofiltration Swale Summary 2. Biofiltration Swale Calculations G. WETPOND CONCEPTUAL DESIGN CALCULATIONS H. LEVEL 1 OFF-SITE ANALYSIS 1. West Basin 2. East Basin A. TECHNICAL INFORMATION REPORT THE ORCHARDS SITE PLAN APPROVAL Page 1 of 2 CONCEPTUAL DRAINAGE PLAN King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PROJECTPART I OWNER AND PART 2 PROJECT PROJECT . DESCRIPTION ProjectOwner Northward Properties Project Name The Orchards Address 1560 140th Ave NE Bellevue Location Phone (2 0 6) 7 4 7—17 2 6 Township 2 3 N Project Engineer Edgar T. Jones, P.E. Section 10 Range 5E Company Dodds Engineers, Inc. Project Size Section AC Address Phone 4205 148th Ave 1 1 -tnu(206) 885-7877 Upstream Drainage Basin Size 114 . 2 AC • Subdivision DOF/G HPA Shoreline Management Short Subdivision COE 404 0 Rockery 0 Grading DOE Dam Safety 0 Structural Vaults Commercial FEMA Floodplain Other ® Other Site Plan Annrnval [] COE Wetlands HPA Prelimina Subdivision COMMUNITYPART 5 SITE r DRAINAGE Community Newcastle Drainage Basin T-nwer C erlar Ri V2r PART 6 SITE CHARACTERISTICS River 0 Floodplain Stream ® Wetlands Critical Stream Reach = Seeps/Springs ® Depress io ns/Swales F] High Groundwater Table 0 Lake 0 Groundwater Recharge Steep Slopes Other Lakeside/Erosion Hazard • Soil Type Slopes Erosion Potential Erosive Velocities Alderwood 1 0 - 2 0 0 Mn(l P-ra t o Norm. Sandy Loam 1 0 - 6 o Slight Everett 2% Slight 0 Additional Sheets Attatched 1/90 Page 2 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT © Ch.4-Downstream Analysis Reduce existing flow rate for selected design 0 storm - see report for specifics a 0 0 0 Additional Sheets Attatched PART 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION ® Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance ( Remove and Restore Temporary ESC Facilities ® Perimeter Runoff Control [0 Clean and Remove All Silt and Debris 0 Clearing and Grading Restrictions ® Ensure Operation of Permanent Facilities ® Cover Practices EX-1 Flag Limits of NGPES ® Construction Sequence Other 0 Other PART 10 SURFACE WATER SYSTEM © Grass Lined Channel 0 Tank Infiltration Method of Analysis © Pipe System C] Vault 0 Depression SBI1H Open Channel 0 Energy Dissapator = Flow Dispersal Compensation/Mitigation Dry Pond LXl Wetland = Waiver of Eliminated Site Storage ® Wet Pond 0 Stream 0 Regional Detention Brief Description of System Operation P..X; gt-; ng nn g; tg wet I a ncl g „g-d for �� ®retie, Pipe collection system to biofiltration swales prior to wetlands; Open Facility Related Site Limitations channels. 0 Additional Sheets Attatched Reference Facility Limitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTSrrRACTS (May require special structural review) FX� Drainage Easement Cast in Place Vault Other ® Access Easement Retaining Wall E] Native Growth Protection Easement Rockery>4'High P�j Tract Structural on Steep Slope Other PART 14 SIGNATURE OF - • • I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the Q attatchments. To the best of my knowledge the information provided �'�• / here is accurate. 1/90 B. PROJECT OVERVIEW B. PROJECT OVERVIEW The proposed project area is approximately 62.3 acres located south of N.E. 8th Street, east of Union Avenue N.E. and west of Duvall Avenue N.E. within the City of Renton. The project site is currently undeveloped except for a small number of single-family residences. The project proposal is for development of the site in a combination of multi-family units, single-family residential lots, single-family townhomes and a small commercial complex. Public and private roadways, parking and recreation areas will be developed in support of the above units and lots. We have prepared these documents in accordance with the Orchards mitigation agreement, the King County Storm Drainage Manual, the predesign meeting on December 19, 1991, and subsequent design meetings and discussions with City of Renton staff. The main points are summarized below. 1. The west basin detention would be provided in Wetland #1 (to be enchanced). Offsite runoff will be directed to a wetland swale traversing the site before entering Wetland #1. Onsite flows shall be biolfiltered prior to entering the detention system. Biofiltration facilities may be located within the wetland buffered areas. Access roads shall be provided to all facilities for maintenance. 2. The majority of the east basin detention would be provided within Wetland #7 located in the southeast portion of the site. Detention shall be provided for the 2 year storm within Wetland #3 central to the site with provisions for overflowing the 100 year storm event. Wetland #4 central to the townhouse portion of the development would also be available for detention. Biofiltration and access shall be required as stated for the west basin. WS 2. EAST BASIN The east onsite basin is 45.9 acres in size. The entire east basin combines to discharge to an existing 36 inch culvert at the south property line within Duvall Avenue NE. The north-central portion of the east basin has five depression areas within it. These areas are dry during the summer months, but contain water within the wetter winter months. All existing hydrograph generations assumed the conservative condition that the depression areas were dry as an initial condition. On and offsite hydrographs were routed through these depression areas for establishing the same discharge requirements as stated above for the west basin. A portion of the detention was provided within wetlands #3 and #4 with the major portion being provided within Wetland #7. Water quality facilities include a wetpond east of Wetland #3 with additional biofiltration swales dispersed throughout the site. C. ONSITE DRAINAGE FEATURES C. ONSITE DRAINAGE FEATURES 1. EXISTING CONDITIONS: The site is divided into an east and west drainage basin. The east basin is approximately 45.9 acres, all tributary to the 36" CMP discharge at the south end of the site on the west side of Duvall Avenue. The north portion of the basin contains a series of interconnected flat depressions which are dry during the summer months, but hold water during the wetter months. Some of the depressed areas have been classified as wetlands. Approximately 30.1 acres of offsite area to the northeast are tributary to this portion of the site. The runoff makes its way through the depressions, travelling generally to the southwest and then changing direction back to the southeast to a roadside ditch on the west side of Duvall Avenue, flowing to south. There is another large wetland in the southwest portion of the basin, east of Duvall Avenue. Offsite runoff from 13.2 acres flows through this wetland along with the onsite area, and is intercepted by a ditch along Duvall Avenue. This ditch also conveys runoff from another 24.4 acres of offsite area, as well as the runoff from the north portion of the onsite basin which crosses Duvall in an 18" culvert. At the south end of the site, the ditch is picked up by a 36" culvert crossing back across Duvall Avenue to the west. From this point the remainder of the east basin is also intercepted and the flows continue offsite to the south in a 36" CMP pipe. The west basin consists of approximately 16.9 acres of onsite area, with 46.5 acres of offsite area tributary to it. Runoff from the offsite area, as well as a small portion of the onsite area, flow into a small depression just south of N.E. 8th Street. It then continues to the southwest in a well defined flat channel that intercepts the majority of the remaining basin runoff. The channel itself has been classified as a wetland area. It flows offsite near the center of the basin and continues to the south, just to the west of the site. Runoff from the strip of area along the west property line sheet flows offsite across rear yards and is intercepted by the channel. Approximately 4.5 acres of the basin in the southwest corner of the site are tributary to a more defined discharge point in that corner, which also leads to rear yards of adjacent properties. 2. DEVELOPED CONDITIONS: The proposed development will continue to maintain the existing east and west drainage basins. Drainage from offsite basins will be collected in tight-line systems and conveyed either through the onsite detention/conveyance systems, or into the conveyance system in Duvall Avenue leading directly to the site discharge point. For the west basin, the development runoff from this onsite area will be collected via a network of catch basins and conveyance piping. Prior to discharging, the drainage will be directed to a 'T' type oil/water separator and then to one of a number of biofiltration swales. The existing channel that traversed the site will be replaced with a large grass-lined Swale, conveying the offsite runoff through the site, prior to entering the detention/wetland facility and ultimately discharging to the existing offsite channel downstream. The onsite runoff will discharge from the biofiltration swales into the wetland enhancement area located in the western area of the single-family development. The wetland enhancement area will be bermed along the south side and affixed with a storm drainage control structure, to double as a storm water detention and treatment basin. The development in the east basin is to be comprised of commercial/office, townhomes, multi-family and single-family. The collection system will consist of the same type of features as described for the west basin. The existing broad swale traversing the basin will be replaced with a grass-lined swale in combination with three existing wetlands which will be enhanced. Flows from the 30.1 acres of offsite area currently entering the north portion of the site will be conveyed directly into the enhanced central wetland. Several onsite sub-basins will also discharge into this wetland after flowing through biofiltration swales or wetponds. A control discharge structure will allow a minimal depth of storm drainage detention in this wetland before the drainage enters the large grass-lined swale. The swale winds to the southeast through the proposed townhomes and into another smaller enhanced wetland within the townhome development. More of the onsite runoff will also be directed into this wetland, following treatment in biofiltration swales. This wetland will be used for detention as well, with a control structure discharging into another section of grass-lined swale flowing southeast to the intersection of Duvall Avenue and N.E. 6th Street. Biofiltration swales and conveyance pipes also converge to this point where a 24" culvert will cross Duvall to the east. The culvert leads to the large enhanced wetland in the southeast corner of the site. This wetland is to be used as the main detention facility with berms placed along the north, west and south sides. The 24.4 acres of offsite area which currently contribute runoff to the roadside ditch in this area, will be intercepted to the north in the conveyance system in Duvall and will bypass the detention pond. The control structure from this enhanced wetland will discharge to the existing 36" culvert crossing back under Duvall to the west. The bypass system also is directed to this pipe. The total combined flow then continues to the south off of the site. (RENTON Q Joins sheet 5) AmC ISSAQUAH 12 M/. 1 10' 1 680000 FEET 12200713010 e ' Il I t n ti% s ' '•i�• - 1 11� AmC Y' r p "• �. E�$ighlan /�'r,= 1 ;1 '1 d . . !• r-j -0 \ ' '1 i 1�i'• S 11 ~.2 i''• _ (: ; t .AgC KOO •','• •• 'J I . 1 Ag :;ti: 1 -� ' r �• AgB •1 An t Trailgr � 1. n •EvB _ 1 a ark. i n .8 nBM B -� :-----i 3 •• 424 y i ■ 11 %.I V 4� I ---T I •�� I• •'• 5h6 F . IMEL 1 Greenwood CE � 'I EvD _i 180 01 1 1 x 1 'hli AgC I ••• FEET •fltOli `+ 11 al •� EvC �� � I � •1• Cem i 19 U °tea`it An 1 a IGRAVEL 'PIT `III 11 i _ I :.•oy �d .. E \ n `• t I A8� � 0321: �C vc\a Itt i u 17= ; tl 11 I .15•. I 141 - I n - AkF EvC I FkF ��1 ... I •II Ir , ti ............. (!r Py ` \j •. I AkF '~ I It •+•t"�1J I I u a ••' 1 /.BM /� ---- 1 — - --••'• ~~' — M ``� ---- =— '/ -- .31 EvB I ---- AgC BM137 AkF I RjvE PYPwOd Ma :^� G g 'I.' �\ \ •{ R� o%fCo� °j'�• 1 „'; ,° �o EvB �. 'j"-- - T- - A t ��gC �Se •AkF I a yrfii �€ tlx ' y l_` Ma x t a AgD SIX, 1 PYit 41 I h •' Pc ° AkF; _ a ap• o xi p 6 pNg I •PY a�ati J 11 455 ?. ." r I`if YElliot P0..=Rh W O a AgC �` AkF I �� x, �� . Ur r'. �� OL r f \\ \ �u I A C AkF Park Ng py 169 ApUEEvC O AgC a. • �—� M I B e AMU AkF i I6 — --- -- -- I — ----o--_ - - 27'3C o- gC ; • a B AgC AgD I AkF• O I { A .428 1 L "7t a w �A' I {� AmC i P AgB i E1m6 AgB _P/PEL AgB Ur I • 1 27 !'• 2 I. `492 1 451 _ o IABC e° Sk n :• ..;.'�`. -t.` '� v e�`G ,.� _� P - AgC --=_,� x . o •, •i A�7UQ,Q•ylT6KbG'- ECG 9 1 A. 470 i., AgB ..... » s--• — �J— -- --- �`; -- I- — -t — EbL • t• w ,x f' 2 I .. . .._... 463 .`IE . .. .�.7 ....itix.. " -._.c - .,. wr«::a tl� •PP . .v:�,, n n A60 - .._I ••w.,:rw..• ,e,� ',.tti ,a .. GUIDE TO.MAPPING UNITS For a full description of a mapping unit, read both the description of the mapping unit and that of the soil series to which the mapping unit belongs. See table 6, page 70, for descriptions of woodland groups. Other .information is given in tables as follows: Acreage and extent, table 1, page 9. Town and country planning, table 4, page 57. Engineering uses of the soils, tables 2 and 3, Recreational uses, table 5, page 64. pages 36 through SS. Estimated yields, table 7, page 79. Woodland Described Capability unit group Map on _ symbol Mapping unit page Symbol Page Symbol AgB Alder ood gravelly sandy loam, 0 to 6 percent slopes---------- 10 IVe-2 76 3d2 AgC Alderood gravelly sandy loam, 6 to 15 percent slopes--------- 8 IVe-2 76 3dl AgD Alderood gravelly sandy loam, 15 to 30 percent slopes-------- 10 VIe-2 78 3dl AkF Alderood and Kitsap soils, very steep------------------------ 10 VIIe-1 78 2dl AmB Arents, Alder ood material, 0 to 6 percent slopes 1/---------- 10 IVe-2 76 3d2 AmC Arents, Alde r ood material, 6 to 15 percent slopes 1/--------- 10 IVe-2 76 3d2 An Arents, Everett material 1/----------------------------------- 11 IVs-1 77 3f3 BeC Beausite gravelly sandy loam, 6 to 1S percent slopes---------- 11 IVe-2 76 3d2 BeD Beausite gravelly sandy loam, 15 to 30 percent slopes--------- 12 VIe-2 78 3d1. BeF Beausite gravelly sandy loam, 40 to 75 percent slopes--------- 12 VIIe-1 78 3d1 Bh Bellingham silt loam------------------------------------------ 12 IIIw-2 76 3w2 Br Briscot silt loam--------------------------------------------- 13 IIw-2 75 3wl Bu Buckley silt loam--------------------------------------------- 13 IIIw-2 76 4wl Cb Coastal beaches----------------------------------------------- 14 VIIIw-1 78 --- Ea Earlmont silt loam-------------------------------------------- 14 IIw-2 75 3w2 Ed Edgewick fine sandy loam-------------------------------------- 15 IIIw-1 75 2ol EvB Everett gravelly sandy loam, 0 to S percent elopes------------ 15 IVs-1 77 3f3 EvC Everett gravelly sandy loam, 5 to 15 percent slopes----------- 16 VIs-1 78 3f3 EvD Everett gravelly sandy loam, 1S to 30 percent slopes---------- 16 Vle-1 77 3f2 EwC Everett-Alder ood gravelly sandy loams, 6 to 15 percent slopes------------------------------------------------------ 16 VIs-1 78 3f3 InA Indianola loamy fine sand, 0 to 4 percent slopes-------------- 17 IVs-2 77 4s3 InC Indianola loamy fine sand, 4 to 15 percent slopes------------- 16 IVs-2 77 4s3 InD Indianola loamy fine sand, 15 to 30 percent slopes------------ 17 VIe-1 76 4s2 KpB Kitsap silt loam, 2 to 8 percent slopes------------------- --- 17 IIIe-1 75 2d2 KpC Kitsap silt loam, 8 to 15 percent slopes---------------------- 18 IVe-1 76 �d2 KpD Kitsap silt loam, 15 to 30 percent slopes--------------------- 18 VIe-2 78 2dl KsC Klaus gravelly loamy sand, 6 to 15 percent slopes------------- 18 VIs-1 78 3fl Ma Mixed alluvial land------------------------------------------- 18 VIw-2 78 2ol NeC Neilton very gravelly loamy sand, 2 to 15 percent slopes------ 19 VIs-1 78 3f3 Ng Newberg silt loam--------------------------------------------- 19 IIw-1 74 2ol Nk Nooksack silt loam-------------------------------------------- 20 IIw-1 74 2ol No Norma sandy loam---------------------------------------------- 20 IIIw-3 76 3w2 Or Orcas peat---------------------------------------------------- 21 VIIIw-1 78 --- Os Oridia silt loam---------------------------------------------- 21 IIw-2 75 3wl OvC Ovall gravelly loam, 0 to 15 percent slopes------------------- 22 IVe-2 76 3dl OvD Ovall gravelly loam, 15 to 25 percent slopes------------------ 23 VIe-2 78 3dl OvF Ovall gravelly loam, 40 to 75 percent slopes------------------ 23 VIIe-1 78 3dl Pc Pilchuck loamy fine sand-------------------------------------- 23 VIw-1 78 2sl Pk Pilchuck fine sandy loam-------------------------------------- 23 IVw-1 76 2sl Pu Puget silty clay loam----------------------------------------- 24 IIIw-2 76 3w2 Py Puyallup fine sandy loam-------------------------------------- 24 IIw-1 74 2ol RaC Ragnar fine sandy loam, 6 to 1S percent slopes---------------- 25 IVe-3 77 4sl RaD Ragnar fine sandy loam, 15 to 25 percent slopes--------------- 26 VIe-2 78 4sl RdC Ragnar-Indianola association, sloping: 1/---------------------- 26 -------- -- Ragnar soil--------------------------------------------- -- IVe-3 77 4sl Indianola soil------------------------------------------- -- IVs-2 77 4s3 RdE Ragnar-Indianola association, moderately steep: 1/------------ 26 -------- -- Ragnar soil--------------------------------------------- -- VIe-2 78 4sl Indianola soil------------------------------------------- -- VIe-1 77 4s2 U.S. GOVERNMENT PRINTING OFFICE:1973 0-468-266 E. ONSITE DETENTION CALCULATIONS 1. ROUTING SUMMARY A summary table of the resultant peak flows is attached below. THE ORCHARDS DEI PROJECT NO. 88008 4-A r-94 WEST EAST BASIN I BASIN EX. 1/2 2 YR PEAK FLOW RATE 1.7 cfs 2.2 cfs DEV. 2 YR PEAK RELEASE RATE 1.7 cfs 2.2 cfs EX. 2 YR PEAK FLOW RATE 3.4 cfs 4.1 cfs DEV. 10 YR PEAK RELEASE RATE 3.4 cfs 4.0 cfs EX. 100 YR, 24 HR PEAK FLOW RATE 16.1 cfs 23.3 cfs DEV. 100 YR, 24 HR PEAK RELEASE RATE 12.3 cfs 14.6 cfs EX. 100 YR, 7 DAY PEAK FLOW RATE 13.4 cfs 19.5 cfs DEV. 100 YR, 7 DAY PEAK RELEASE RAT 12.5 cfs 18.4 cfs 2 YR DETENTION VOLUME (cu-ft) 21,166 221,309 10 YR DETENTION VOLUME (cu-ft) 35,644 342,702 100 YR, 24 HR DETENTION VOLUME cu-ft 62,390 428,100 100 YR, 7 DAY DETENTION VOLUME (cu-f 63,508 450,568 4. DEVELOPED SITE HYDROLOGY As previously discussed, the developed drainage system will continue to split the site into two drainage basins. a. WEST BASIN: The proposed design for the west basin involves the use of the existing wetland #1 for detention. Due to site constraints, a developed area slightly less than the existing west basin will be tributary to the detention system. The remaining area will be directed to the main east detention pond, but the developed discharges will be designed to match the existing peak flows of either basin. "Z": 13.6 acres, tributary to main west detention system (100) 4.70 ac, impervious @ CN =98 7.20 ac, landscaping/wetland/brush @ CN = 84.5 Time of Concentration: estimated at 25 minutes b. EAST BASIN: The developed east basin will be divided into three sub-basins, each tributary to one of the enhanced wetlands to be used for storm drainage detention/water quality facilities. "W: 2.80 acres, tributary to the southeast detention system (300) 1.22 ac, impervious @ CN =98 1.60 ac, landscape/brush @ CN = 85 Time of Concentration: estimated at 20 minutes "W": 8.1 acres, tributary to the second wetland (400) 3.6 ac, impervious @ CN = 98 4.5 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 25 minutes "X": 14.52 acres, tributary to the first wetland (200) 4.72 ac, impervious @ CN = 98 9.8 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes "Y": 23.3 acres, tributary to the third wetland (300) 10.4 ac, impervious @ CN = 98 12.9 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes A developed drainage map is included in this section along with Basin Summary printouts and basin flow summaries. Al r 16 I? B ,B 20 Y. �.I 22 23 `33 16 I ry is i la 13 I f2 I i 1O \._ / 64�/(/(f 6S I 67 1' a@A '� \ /•I '.e 200 ti l q 751 10 77 ?� � ..•e �=«.•• .0 � .4 't � mot. a 7 �.1 1�71, awVrr; 7e 79 --7' 90 ,. •gl v�9G -d� l) z `.,' ' rl 1 1 'o oYy. \°.•/ ` /�. , ' - -1 i �I .,��'l` y�l I I.I I)'ll I n I'j l01 96 I 97 I 99 1 og I l00 ,' •`• _ ti� r� ,.r• \�'�,. � � AI sl ED ,erg e '•,�>;�_.��^_,_ � '_ g;l � `��, (=�_ � � � I;� ` w', — ,I II, i;.;;/,., r: ,;f-'jam �_ : - �I - �._, I` � _, �... I � w1� •�. ��� : Iv wee li'., 3zc.•e. ; '.J a! '' �_ ` III! TI �- JJ n, �Q -/^T'• � IJ l DEVELOPED ONSITE BASINS -L;L DEI #88008 / THE ORCHARDS c esr'm,r.w ''�.•r_.. 2/5/92 BY-GRS H. LEVEL 1 OFF-SITE ANALYSIS 1. WEST BASIN The west basin discharges across the south property line of Sector A fronting Union Ave NE. Drainage flows southerly offsite through a wide open swale for approximately 250 feet before crossing beneath a gravel driveway via an 18 inch vitrified clay pipe. The pipe crown is damaged and is bridged by a steel half-round culvert. The culvert is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southerly for 350 feet in the swale before crossing beneath another gravel driveway via an 18 inch concrete culvert. The pipe is in good condition but is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southwesterly for 250 feet before being intercepted by a 24" culvert that is stubbed out from the Union Avenue N.E. trunk, which is also 24" in size. From this point the runoff flows south in the Union Avenue storm drainage system. 2. EAST BASIN The areas to be analyzed or discussed in more detail are indicated by [#]. Runoff from the northern portion of the east basin (north of N.E. 6th Street) crosses Duvall Avenue N.E. to the east in an 18" concrete culvert [1] at the 6th Street intersection. The runoff from the remainder of the offsite area and the onsite area east of Duvall Avenue, joins this flow in the roadside ditch and existing wetland area, continuing to the south for 650'. It then crosses back under Duvall Avenue to the west in a 36" concrete culvert [2]. On the west side of the road at the south edge of the site, runoff from the remaining onsite area is added and the flow is directed south for 80' in a 36" CMP culvert [3]. The culvert discharges into an open swale, flowing southwest for approximately 600' where it is received by a 30" CMP culvert system [4] conveying it through the Windsor Place Apartments for 370' to the west property line of Windsor Place. From here the flow is directed into a rocked channel that flows 150' westerly to a pair of 20' culverts[5], one 12" and one 18", crossing an old access road. The rocked channel then continues southwesterly for 170' to an 18" concrete culvert [6]approximately 30' long, crossing an access road to a water pump house along N.E. 4th Street. The culvert discharges into a short section of open swale leading to a 36" concrete culvert [7] crossing N.E. 4th Street to the south. From here the flows enter a channel [8] leading west along 4th Street for approximately 100' and it then turns and continues to the south. From the previous drainage analysis and additional downstream basin analysis up to the Windsor Place Apartments, the following peak flow rates were obtained: 10 year developed = 4.7 cfs 100 year developed = 16.3 cfs 100 year existing = 25.2 cfs [1] 18" concrete culvert crossing Duvall Avenue N.E. - This culvert is listed in the Maplewood Drainage Basin Study as having capacity problems for 100 year events. The slope is 0.6%, length is 85'. The capacity is 8.8 cfs flowing full. There is approximately 3' of headwater depth available to push more flow through the pipe. However, this culvert will be replaced and resized as part of the Orchards development, so capacity will not be an issue. [2] 36" concrete culvert crossing Duvall Avenue N.E. - The slope is 2.3%, length is 110'. Capacity is 119.6 cfs flowing full, or 35 cfs with no headwater over the pipe entrance. Therefore, capacity is not a problem. [3] 36" CMP culvert along west side of Duvall Avenue N.E. - The slope is 1%, length is 80'. Capacity is 36.1 cfs flowing full, or 35 cfs with no headwater over the top of the pipe entrance. Therefore, capacity is not a problem. [4] 30"CMP culvert system through Windsor Place - The minimum slope is 0.8%. The capacity flowing full is 19.9 cfs. This is also listed as a flooding problem. While some headwater buildup would be necessary to convey the existing 100 year storm event, the reduced flow from the Orchards detention system should not be a capacity problem. There are some constrictions placed in the open channel, presumably by the property owner, leading to the culvert which may cause some minor flooding, but nothing of concern. Specifically, a 12" pipe under a small trail would cause the flows to overtop the trail, but the flow would still be contained. [5] 12" and 18" culverts in rocked channel. - The Windsor Place plans show that these culverts were to be abandoned and the channel was to go through the existing access road. The road was to be blocked off. However, even if the flows must overtop the road due to culvert capacity problems, they would easily be contained within the immediate area of the swale. [6] 18" concrete culvert at the water pump house - The slope is approximately 2%. The capacity is 16.1 cfs. There will be a slight headwater buildup to convey the 100 year storm event, and the available headwater depth is more than adequate. [7] 36" concrete culvert crossing N.E. 4th Street - The slope is 0.5%. The capacity is 51 cfs flowing full. Capacity is not a problem. [8] Channel along N.E. 4th Street - This is also listed as being restricted by the Maplewood Drainage Basin Study. The study calls for reconstruction of the channel. Our field inspection verifies this observation. The channel has a negative slope of approximately 2' along 4th Street before it turns to the south. It has adequate depth but needs to be regraded. As it exists, it still has the capacity to convey the 100 year storm, but would likely cause water to back up though to the north side of N.E. 4th Street. In a City of Renton memo to Mary Lynn Myer from Randall Parsons, dated January 21, 1991, the drainage concerns above, along with erosion problems further downstream, were discussed. The recommendation was made to over-detain on the Orchards project for the 2-year storm (releasing at 50% of the existing 2-year peak flow rate) and for the 10-year storm (releasing at the existing 2-year peak flow rate). Additionally, the existing 100-year peak flow rate would have to be matched or decreased for the developed 100-year storm event. These criteria have been met or exceeded by this preliminary design for the Orchards project. Q - y ODDS ENGINEERS, INC. CI V IL ENGINf= ERING SURVEYING PLANNING Ms. Kayren Kittrick February 2, 1996 Public Works Department DEI Project No. 95054 City of Renton 200 Mill Avenue South Renton, WA 98055 Subject: The,Orchards, Sectors E, F and G Detention Calculations Dear Kayren: Enclosed are portions of the original overall storm drainage calculations for the Orchards site. Included in these calculations are the areas of Sectors E/F and G. The current development proposed on these parcels differs in concept from the original design, so I have prepared this comparison between the original and proposed land uses. As you are aware, the detention volume required is directly related to the amount of impervious area on a site. In order to verify that the design volumes in the original design are adequate for the modified land use now proposed, I have calculated the amount of impervious area to show that there is not an increase which would necessitate adding more storage volume. The original calculations assumed a tributary basin of 23.3 acres which included all of sectors E/F and G, as well as part of sector C and N.E. 6th Street. The total impervious area was 10.4 acres. The new layout for sectors E/F has an impervious area of 4.0 acres and Sector G has 3.5 acres. The portions of sector C and N.E. 6th Street that are part of the original basin 'Y' account for 2.8 acres impervious. This is a proposed total of 10.3 acres, which is slightly less than the design acreage of 10.4. Since the proposed developments are hydrologically comparable to the design basin, the detention facility, as designed, will be adequate. If you have any questions or comments please call Ed Jones or me at 885-7877. Sincerely, SHAib DODDS ENGINEERS, INC. .�40� As, r w Ole!"E�0�M 1996 c/ryo R�iy aNNiHc a s w.Q Gary R. Sharnbroich, P.E. ssf STE���y� O F Project Engineer/Associate NAL EXPIRES 12/28/ q Z•Z q(P 4205 1 48TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 (206) 885-7877 FAX: (206) 885-7963 DODDS ENGINEERS, INC. CIVIL ENGINEE RING S U R V E Y I N G P L A N N I N G STORM, DRAINAGE CALCULATIONS I{OR I -enar-ed By: Gary R. Sicatnibr€rich, AF;proved By: Edgar T, Janes, P.E. 01�1 VA DA .I. Pro Date: April 4, 1994 "l-a Z ' EXPIRES 12/28 4 •9 4205 148TH AVE. N.E., SUITE 200-BELLEVUE, WA 08007 [206) 885-7B77 OR 454-3743 FAX:[206)BB5-7963 TABLE OF CONTENTS A. TECHNICAL INFORMATION REPORT B. PROJECT OVERVIEW C. ONSITE DRAINAGE FEATURES 1. Existing 2. Proposed D. CORE AND SPECIAL REQUIREMENTS 1. CR#1 - Discharge at the Natural Location 2. CR#2 - Off-site Analysis 3. CR#3 - Runoff Control 4. CR#4 - Conveyance System 5. CR#5 - Erosion / Sedimentation Control Plan 6. CR#6 - Maintenance and Operation 7. CR#7 - Bonds and Liability 8. SR#1 - Critical Drainage Areas 9. SR#2 - Existing Master Drainage Plan 10. SR#3 - Master Drainage Plan 11. SR#4 - Basin and Community Plans 12. SR#5 - Special Water Quality Controls 13. SR#6 - Coalescing Plate Oil/Water Separators 14. SR#7 - Closed Depressions 15. SR#8 - Use of Lakes,Wetlands or Closed Depressions for Peak Runoff Quantity Control 16. SR#9 - Delineation of the 100 Year Floodplain 17. SR#10 - Flood Protection Facilities for the Type 1 and 2 Streams 18. SR#11 - Geotechnical Analysis and Report 19. SR#12 - Soils Analysis and Report E. ONSITE DETENTION CALCULATIONS 1. Preliminary Routing Summary 2. Existing Site Hydrology a. West Basin b. East Basin 3. Existing Upstream Mite Hydrology a. West Basin b. East Basin 4. Developed Site Hydrology a. West Basin b. East Basin 5. Hydrology Analysis a. West Basin b. East Basin F. BIOFILTRATION DESIGN CALCULATION 1. Biofiltration Swale Summary 2. Biofiltration Swale Calculations G. WETPOND CONCEPTUAL DESIGN CALCULATIONS H. LEVEL 1 OFF-SITE ANALYSIS 1. West Basin 2. East Basin A. TECHNICAL INFORMATION REPORT THE ORCHARDS SITE PLAN APPROVAL Page 1 of 2 CONCEPTUAL DRAINAGE PLAN King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET LOCATIONPART I PROJECT OWNER AND PART 2 PROJECT PROJECT ENGINEER AND DESCRIPTION ProjectOwner Northward Properties Project Name The Orchards Address 1560 140th Ave NE Bellevue Location Phone (2 0 6) 7 4 7-17 2 6 Township 2 3 N Project Engineer Edgar T. Jones, P.E. Range 5E Company Dodds Engineers, Inc. Section 10 Project Size 62 • 3 AC Address Phone 4205 148th Ave NE Bellevue(206) 885-7877 Upstream Drainage Basin Size 114 . 2 AC PART 3 TYPE OF Subdivision 0 DOF/G HPA Shoreline Management Short Subdivision COE 404 Rockery Grading 0 DOE Dam Safety Structural Vaults Commercial FEMA Floodplain Other ® Other Site Plan L=rc)val ] COE Wetlands 0 HPA Preliminary Subdivision COMMUNITYPART 5 SITE r DRAINAGE Community Newcastle Drainage Basin Lower Cp.(�Pr Rijn-r PARTS SITE CHARACTERISTICS River Floodplain 0 Stream ® Wetlands 0 Critical Stream Reach = Seeps/Springs ® Depressions/Swales = High Groundwater Table Lake = Groundwater Recharge Steep Slopes Other 0 Lakeside/Erosion Hazard • Soil Type Slopes Erosion Potential Erosive Velocities Alderwood 10 — 2 0° Mc�r7 Pra to Norm. Sandy Loam 1 0 - 6 o Slight Everett 20 S1 ; rr t Additional Sheets Attatched 1/90 Page 2 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET DEVELOPMENTPART 8 REFERENCE LIMITATION/SITE CONSTRAINT © Ch.4-Downstream Analysis Reduce existing flow rate for selected design 0 storm — see report for specifics a 0 a Additional Sheets Attatched PART 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION ® Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance ] Remove and Restore Temporary ESC Facilities ® Perimeter Runoff Control ] Clean and Remove All Silt and Debris 0 Clearing and Grading Restrictions C—JX Ensure Operation of Permanent Facilities ® Cover Practices nX Flag Limits of NGPES ® Construction Sequence Other Other PART 10 SURFACE WATER SYSTEM © Grass Lined Channel 0 Tank 0 Infiltration Method of Analysis © Pipe System Vault 0 Depression SBI TT Open Channel Energy Dissapator = Flow Dispersal Compensation/Mitigation Dry Pond Wetland 0 Waiver of Eliminated Site Storage ® Wet Pond Stream = Regional Detention Brief Description of System Operation _F 1gf-; nn nnS1tP wPtlanr9g Ltiser. fog dj@.kentien; Pipe collection system to biofiltration swales prior to wetlands;ands; non Facility Related Site Limitations channels. Additional Sheets Attatched Reference Facility Limitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTSITRACTS (May require special structural review) X� Drainage Easement 0 Cast in Place Vault Other ® Access Easement 0 Retaining Wall M Native Growth Protection Easement 0 Rockery>4'High PC� Tract Structural on Steep Slope Other PART 14 SIGNATURE OF - • I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the A. �•� attatchments. To the best of my knowledge the information provided here is accurate. ry,wavr. 1/90 B. PROJECT OVERVIEW B. PROJECT OVERVIEW The proposed project area is approximately 62.3 acres located south of N.E. 8th Street, east of Union Avenue N.E. and west of Duvall Avenue N.E. within the City of Renton. The project site is currently undeveloped except for a small number of single-family residences. The project proposal is for development of the site in a combination of multi-family units, single-family residential lots, single-family townhomes and a small commercial complex. Public and private roadways, parking and recreation areas will be developed in support of the above units and lots. We have prepared these documents in accordance with the Orchards mitigation agreement, the King County Storm Drainage Manual, the predesign meeting on December 19, 1991, and subsequent design meetings and discussions with City of Renton staff. The main points are summarized below. 1. The west basin detention would be provided in Wetland #1 (to be enchanced). Offsite runoff will be directed to a wetland swale traversing the site before entering Wetland #1. Onsite flows shall be biolfiltered prior to entering the detention system. Biofiltration facilities may be located within the wetland buffered areas. Access roads shall be provided to all facilities for maintenance. 2. The majority of the east basin detention would be provided within Wetland #7 located in the southeast portion of the site. Detention shall be provided for the 2 year storm within Wetland #3 central to the site with provisions for overflowing the 100 year storm event. Wetland #4 central to the townhouse portion of the development would also be available for detention. Biofiltration and access shall be required as stated for the west basin. 2. EAST BASIN The east onsite basin is 45.9 acres in size. The entire east basin combines to discharge to an existing 36 inch culvert at the south property line within Duvall Avenue NE. The north-central portion of the east basin has five depression areas within it. These areas are dry during the summer months, but contain water within the wetter winter months. All existing hydrograph generations assumed the conservative condition that the depression areas were dry as an initial condition. On and offsite hydrographs were routed through these depression areas for establishing the same discharge requirements as stated above for the west basin. A portion of the detention was provided within wetlands #3 and #4 with the major portion being provided within Wetland #7. Water quality facilities include a wetpond east of Wetland #3 with additional biofiltration swales dispersed throughout the site. C. ONSITE DRAINAGE FEATURES C. ONSITE DRAINAGE FEATURES 1. EXISTING CONDITIONS: The site is divided into an east and west drainage basin. The east basin is approximately 45.9 acres, all tributary to the 36" CMP discharge at the south end of the site on the west side of Duvall Avenue. The north portion of the basin contains a series of interconnected flat depressions which are dry during the summer months, but hold water during the wetter months. Some of the depressed areas have been classified as wetlands. Approximately 30.1 acres of offsite area to the northeast are tributary to this portion of the site. The runoff makes its way through the depressions, travelling generally to the southwest and then changing direction back to the southeast to a roadside ditch on the west side of Duvall Avenue, flowing to south. There is another large wetland in the southwest portion of the basin, east of Duvall Avenue. Offsite runoff from 13.2 acres flows through this wetland along with the onsite area, and is intercepted by a ditch along Duvall Avenue. This ditch also conveys runoff from another 24.4 acres of offsite area, as well as the runoff from the north portion of the onsite basin which crosses Duvall in an 18" culvert. At the south end of the site, the ditch is picked up by a 36" culvert crossing back across Duvall Avenue to the west. From this point the remainder of the east basin is also intercepted and the flows continue offsite to the south in a 36" CMP pipe. The west basin consists of approximately 16.9 acres of onsite area, with 46.5 acres of offsite area tributary to it. Runoff from the offsite area, as well as a small portion of the onsite area, flow into a small depression just south of N.E. 8th Street. It then continues to the southwest in a well defined flat channel that intercepts the majority of the remaining basin runoff. The channel itself has been classified as a wetland area. It flows offsite near the center of the basin and continues to the south, just to the west of the site. Runoff from the strip of area along the west property line sheet flows offsite across rear yards and is intercepted by the channel. Approximately 4.5 acres of the basin in the southwest corner of the site are tributary to a more defined discharge point in that corner, which also leads to rear yards of adjacent properties. 2. DEVELOPED CONDITIONS: The proposed development will continue to maintain the existing east and west drainage basins. Drainage from offsite basins will be collected in tight-line systems and conveyed either through the onsite detention/conveyance systems, or into the conveyance system in Duvall Avenue leading directly to the site discharge point. For the west basin, the development runoff from this onsite area will be collected via a network of catch basins and conveyance piping. Prior to discharging, the drainage will be directed to a 'T' type oil/water separator and then to one of a number of biofiltration swales. The existing channel that traversed the site will be replaced with a large grass-lined swale, conveying the offsite runoff through the site, prior to entering the detention/wetland facility and ultimately discharging to the existing offsite channel downstream. The onsite runoff will discharge from the biofiltration swales into the wetland enhancement area located in the western area of the single-family development. The wetland enhancement area will be bermed along the south side and affixed with a storm drainage control structure, to double as a storm water detention and treatment basin. The development in the east basin is to be comprised of commercial/office, townhomes, multi-family and single-family. The collection system will consist of the same type of features as described for the west basin. The existing broad swale traversing the basin will be replaced with a grass-lined swale in combination with three existing wetlands which will be enhanced. Flows from the 30.1 acres of offsite area currently entering the north portion of the site will be conveyed directly into the enhanced central wetland. Several onsite sub-basins will also discharge into this wetland after flowing through biofiltration swales or wetponds. A control discharge structure will allow a minimal depth of storm drainage detention in this wetland before the drainage enters the large grass-lined swale. The swale winds to the southeast through the proposed townhomes and into another smaller enhanced wetland within the townhome development. More of the onsite runoff will also be directed into this wetland, following treatment in biofiltration swales. This wetland will be used for detention as well, with a control structure discharging into another section of grass-lined swale flowing southeast to the intersection of Duvall Avenue and N.E. 6th Street. Biofiltration swales and conveyance pipes also converge to this point where a 24" culvert will cross Duvall to the east. The culvert leads to the large enhanced wetland in the southeast corner of the site. This wetland is to be used as the main detention facility with berms placed along the north, west and south sides. The 24.4 acres of offsite area which currently contribute runoff to the roadside ditch in this area, will be intercepted to the north in the conveyance system in Duvall and will bypass the detention pond. The control structure from this enhanced wetland will discharge to the existing 36" culvert crossing back under Duvall to the west. The bypass system also is directed to this pipe. The total combined flow then continues to the south off of the site. (RENTON Q Joins sheet 5) AMC ISSAQUAH 12 MI. 1 10' 1 680000 FEET 1220 T30' {- 470 AMC a $ghlar i /�-\,=Sch 1 i I a /2 ? • Pr.%� sd µ$3 do ss 1: ; .. AgC:149- ���, �• AgB / \\ • .i An o u• fir': 4 . • Trailgr � „ n.Ev8 *on ■• a ' ark,'. 6 I Greenwood C'e n I '' t�" EvD 1800 V I , AgC I .ri:. . FEET 406 •fIt 01i� �� n n I _ •:. EvC iJ .:%< U aaa q An n '{ r GRAVEL °PIT „1\ It aaaa f\ • II� AI f r -•. .. B321: tC �aaa It gC14 l - - --- AI „�'~PSG• I ° �� S: o?P AkF Ev IP C kF Icl \ ` ,�, L.-- --- �a -4b� •.r- ~� J _ i� I •• tip` 1 Ur Py •'� r / / I , `\J I ✓ AkF I ,,• it• n *�' °��'.. / EvB AgC BM37 - AkF —�Ij,Ly, C -- - `Ma Py AgC ( z ii EvB 5. I } t -; � -� -ter •_ ••. - AkF 1' +i. ° �: ° •o r A D �X ` ,•,,w• \_' �P 10 I, ♦ AkF =. a Ng mac_ it Z•11 ..___••. . '21 a "�` a . h 455 E11ot AgC \I,`� AkF I 11 �. a alp Ur S Syr' 1161 a I Arc u\'1 AkF rPark I• f ,1 I Ng f �. Py a \° \ 169 r a Ur \Z�p �.b•°� AgCEvC I �� L�J 1 I AgD AkF • M B 2 yam, 76 - - -- 1 -- 4r�. • ° --- BMp 0 BM Nlk ,.AgC yt\� CAgC ` AgD - I AkF > AMC " I AgBlll emg i AB —PIPELINE—AgC- AgB .` Ur 1 27 \4921 2- 451 \ ? o IAgC e •••. :.1k I Sk I .� 71 = L AgC No Sk a •�C I o�::1% I o 5hip•' • • tAgB • •y'. PE RQ's1T6Kac', E11 v I c` ) Q B 47093 ap ♦ E 4 3 ._� ... . �, _, .:i,.c. ..t.4 .•,. .-.... ..,,., .rr.ii 1 P . ...•... � .. . A...\A68 . -. 5:....,1 .., u..rs. .. .... .. .t� .... _ .,.. GUIDE TO.MAPPING UNITS For a full description of a mapping unit, read both the description of the mapping unit and that of the soil series to which the mapping unit belongs. See table 6, page 70, for descriptions of woodland groups. Other .information is given in tables as follows: Acreage and extent, table 1, page 9. Town and country planning, table 4, page 57. Engineering uses of the soils, tables 2 and 3, Recreational uses, table 5, page 64. pages 36 through 55. Estimated yields, table 7, page 79. Woodland Described Capability unit group Map on symbol Mapping unit page Symbol Page Symbol AgB Alderwood gravelly sandy loam, 0 to 6 percent slopes---------- 10 IVe-2 76 3d2 AgC Alderwood gravelly sandy loam, 6 to 15 percent slopes--------- 8 IVe-2 76 3dl AgD Alderwood gravelly sandy loam, 15 to 30 percent slopes-------- 10 VIe-2 78 3dl AkF Alderwood and Kitsap soils, very steep------------------------ 10 VIIe-1 78 2dl AmB Arents, Alderwood material, 0 to 6 percent slopes 1/---------- 10 IVe-2 76 3d2 AmC Arents, Alderwood material, 6 to 15 percent slopes 1/--------- 10 IVe-2 76 3d2 An Arents, Everett material 1/----------------------------------- 11 IVs-1 77 3f3 BeC Beausite gravelly sandy loam, 6 to 15 percent slopes---------- 11 IVe-2 76 3d2 BeD Beausite gravelly sandy loam, 15 to 30 percent slopes--------- 12 VIe-2 78 3d1. BeF Beausite gravelly sandy loam, 40 to 7S percent slopes--------- 12 VIIe-1 78 3dl Bh Bellingham silt loam------------------------------------------ 12 IIIw-2 76 3w2 By Briscot silt loam--------------------------------------------- 13 IIw-2 75 3wl Bu Buckley silt loam--------------------------------------------- 13 IIIw-2 76 4wl Cb Coastal beaches----------------------------------------------- 14 VIIIw-1 78 --- Ea Earlmont silt loam-------------------------------------------- 14 IIw-2 75 3w2 Ed Edgewick fine sandy loam-------------------------------------- 15 IIIw-1 75 2ol EvB Everett gravelly sandy loam, 0 to 5 percent slopes------------ 15 IVs-1 77 3f3 EvC Everett gravelly sandy loam, 5 to 1S percent slopes----------- 16 VIs-1 78 3f3 EvD Everett gravelly sandy loam, 15 to 30 percent slopes---------- 16 Vle-1 77 3f2 EwC 'Everett-Alderwood gravelly sandy loams, 6 to 15 percent slopes------------------------------------------------------ 16 VIs-1 78 3f3 InA Indianola loamy fine sand, 0 to 4 percent slopes-------------- 17 IVs-2 77 4s3 InC Indianola loamy fine sand, 4 to 15 percent slopes------------- 16 IVs-2 77 4s3 InD Indianola loamy fine sand, 15 to 30 percent slopes------------ 17 VIe-1 76 4s2 KpB Kitsap silt loam, 2 to 8 percent slopes------------------- --- 17 IIIe-1 75 2d2 KpC Kitsap silt loam, 8 to 15 percent slopes---------------------- 18 IVe-1 76 �d2 KpD Kitsap silt loam, 15 to 30 percent slopes--------------------- 18 VIe-2 78 2dl KsC Klaus gravelly loamy sand, 6 to 15 percent slopes------------- 18 VIs-1 78 3fl Ma Mixed alluvial land------------------------------------------- 18 VIw-2 78 2ol NeC Neilton very gravelly loamy sand, 2 to 15 percent slopes------ 19 VIs-1 78 3f3 Ng Newberg silt loam--------------------------------------------- 19 IIw-1 74 2ol Nk Nooksack silt loam-------------------------------------------- 20 IIw-1 74 2ol No Norma sandy loam---------------------------------------------- 20 IIIw-3 76 3w2 Or Orcas peat---------------------------------------------------- 21 VIIIw-1 78 --- Os Oridia silt loam---------------------------------------------- 21 IIw-2 75 awl OvC Ovall gravelly loam, 0 to 15 percent slopes------------------- 22 IVe-2 76 3dl OvD Ovall gravelly loam, 1S to 25 percent slopes------------------ 23 VIe-2 78 3dl OvF Ovall gravelly loam, 40 to 75 percent slopes------------------ 23 VIIe-1 78 3d1 Pc Pilchuck loamy fine sand-------------------------------------- 23 VIw-1 78 2sl Pk Pilchuck fine sandy loam-------------------------------------- 23 IVw-1 76 2sl Pu Puget silty clay loam----------------------------------------- 24 IIIw-2 76 3w2 Py Puyallup fine sandy loam-------------------------------------- 24 IIw-1 74 2ol RaC Ragnar fine sandy loam, 6 to 15 percent slopes---------------- 25 IVe-3 77 4sl RaD Ragnar fine sandy loam, 15 to 2S percent slopes--------------- 26 VIe-2 78 4sl RdC Ragnar-Indianola association, sloping: 1/---------------------- 26 -------- -- Ragnar soil--------------------------------------------- -- IVe-3 77 4sl Indianola soil------------------------------------------- -- IVs-2 77 4s3 RdE Ragnar-Indianola association, moderately steep: 1/------------ 26 -------- -- Ragnar soil--------------------------------------------- -- VIe-2 78 4sl Indianola soil------------------------------------------- -- VIe-1 .77 4s2 U.S. GOVERNMENT PRINTING OFFICE:1973 0-466-266 E. ONSITE DETENTION CALCULATIONS 1. ROUTING SUMMARY A summary table of the resultant peak flows is attached below. sum THE ORCHARDS DEI PROJECT NO. 88008 4-A r-94 WEST EAST BASIN BASIN EX. 1/2 2 YR PEAK FLOW RATE 1.7 cfs 2.2 cfs DEV. 2 YR PEAK RELEASE RATE 1.7 cfs 2.2 cfs EX. 2 YR PEAK FLOW RATE 3.4 cfs 4.1 cfs DEV. 10 YR PEAK RELEASE RATE 3.4 cfs 4.0 cfs EX. 100 YR, 24 HR PEAK FLOW RATE 16.1 cfs 23.3 cfs DEV. 100 YR, 24 HR PEAK RELEASE RATE 12.3 cfs 14.6 cfs EX. 100 YR, 7 DAY PEAK FLOW RATE 13.4 cfs 19.5 cfs DEV. 100 YR, 7 DAY PEAK RELEASE RAT 12.5 cfs r 18.4 cfs 2 YR DETENTION VOLUME (cu-ft) 21,166 221,309 10 YR DETENTION VOLUME (cu-ft) 35,644 342,702 100 YR, 24 HR DETENTION VOLUME cu-ft 62,390 428,100 100 YR, 7 DAY DETENTION VOLUME (cu-f 63,508 450,568 4. DEVELOPED SITE HYDROLOGY As previously discussed, the developed drainage system will continue to split the site into two drainage basins. a. WEST BASIN: The proposed design for the west basin involves the use of the existing wetland #1 for detention. Due to site constraints, a developed area slightly less than the existing west basin will be tributary to the detention system. The remaining area will be directed to the main east detention pond, but the developed discharges will be designed to match the existing peak flows of either basin. "Z": 13.6 acres, tributary to main west detention system (100) 4.70 ac, impervious @ CN = 98 7.20 ac, landscaping/wetland/brush @ CN = 84.5 Time of Concentration: estimated at 25 minutes b. EAST BASIN: The developed east basin will be divided into three sub-basins, each tributary to one of the enhanced wetlands to be used for storm drainage detention/water quality facilities. "W: 2.80 acres, tributary to the southeast detention system (300) 1.22 ac, impervious @ CN = 98 1.60 ac, landscape/brush @ CN = 85 Time of Concentration: estimated at 20 minutes "W": 8.1 acres, tributary to the second wetland (400) 3.6 ac, impervious @ CN =98 4.5 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 25 minutes . t "X": 14.52 acres, tributary to the first wetland (200) 4.72 ac, impervious @ CN = 98 9.8 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes "Y": 23.3 acres, tributary to the third wetland (300) 10.4 ac, impervious @ CN = 98 12.9 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes A developed drainage map is included in this section along with Basin Summary printouts and basin flow summaries. i Iel I I " 15 16 I' 16 a 20 ?6 22 '•' 2' . �•.1. 1. �� i 1,�� _ �--.. 1�``'i. �3�. % �..r I !i•�i / /' \ 4 •4 33 /% I yi�r' _III L�---�t�' •,/ ,I ti� ,�'�_��,I d< � `� \� �- � i ��,I I I: 27 W, 16 - _ ' •n -- -..���--- of ' `3 < f rf <7 I /\\^ tc0 �.38 / 3B - 57 � 56 �. _ � �t � -f3�• ?9 i. 1V11,,�,1 57 13 M R I p 64 66 67 �92 '''r_ 90+'} e9• `^-s� sT'' `6 `�.. * � � �.�—�FJX��I"'" I 61 I� � •�I a _ -.,f 'ill •' I. .. —_ a r- —_�� —�— _ W_._. _ �_- --�=r��— _ 14 73 pp 76 77 Ps f !ui IN ti TLi '"i i��i__-�1.£ —, 1�I' � •� �I .,r \\�, ..w, a• ,1 =,1,,,• y�. �Q �.�•^ O� .� -,�` N ee 11 32•w a<.,a• .? � fs• "I'� \ : l l I I a 300 DEVELOPED 1J' i ONSITE BASINS •I: ,.� : ; ; , �, J .� •�; DEI #88008 / THE ORCHARDS i 2/5/92 BY-GRS H. LEVEL 1 OFF-SITE ANALYSIS 1. WEST BASIN The west basin discharges across the south property line of Sector A fronting Union Ave NE. Drainage flows southerly offsite through a wide open Swale for approximately 250 feet before crossing beneath a gravel driveway via an 18 inch vitrified clay pipe. The pipe crown is damaged and is bridged by a steel half-round culvert. The culvert is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southerly for 350 feet in the swale before crossing beneath another gravel driveway via an 18 inch concrete culvert. The pipe is in good condition but is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southwesterly for 250 feet before being intercepted by a 24" culvert that is stubbed out from the Union Avenue N.E. trunk, which is also 24" in size. From this point the runoff flows south in the Union Avenue storm drainage system. 2. EAST BASIN The areas to be analyzed or discussed in more detail are indicated by [#]. Runoff from the northern portion of the east basin (north of N.E. 6th Street) crosses Duvall Avenue N.E. to the east in an 18" concrete culvert [1] at the 6th Street intersection. The runoff from the remainder of the offsite area and the onsite area east of Duvall Avenue, joins this flow in the roadside ditch and existing wetland area, continuing to the south for 650'. It then crosses back under Duvall Avenue to the west in a 36" concrete culvert [2]. On the west side of the road at the south edge of the site, runoff from the remaining onsite area is added and the flow is directed south for 80' in a 36" CMP culvert [3]. The culvert discharges into an open swale, flowing southwest for approximately 600' where it is received by a 30" CMP culvert system [4] conveying it through the Windsor Place Apartments for 370' to the west property line of Windsor Place. From here the flow is directed into a rocked channel that flows 150' westerly to a pair of 20' culverts[5], one 12" and one 18", crossing an old access road. The rocked channel then continues southwesterly for 170' to an 18" concrete culvert [6]approximately 30' long, crossing an access road to a water pump house along N.E. 4th Street. The culvert discharges into a short section of open swale leading to a 36" concrete culvert [7] crossing N.E. 4th Street to the south. From here the flows enter a channel [8] leading west along 4th Street for approximately 100' and it then turns and continues to the south. From the previous drainage analysis and additional downstream basin analysis up to the Windsor Place Apartments, the following peak flow rates were obtained: 10 year developed = 4.7 cfs 100 year developed = 16.3 cfs 100 year existing = 25.2 cfs [1] 18" concrete culvert crossing Duvall Avenue N.E. - This culvert is listed in the Maplewood Drainage Basin Study as having capacity problems for 100 year events. The slope is 0.6%, length is 85'. The capacity is 8.8 cfs flowing full. There is approximately 3' of headwater depth available to push more flow through the pipe. However, this culvert will be replaced and resized as part of the Orchards development, so capacity will not be an issue. [2] 36" concrete culvert crossing Duvall Avenue N.E. - The slope is 2.3%, length is 110'. Capacity is 119.6 cfs flowing full, or 35 cfs with no headwater over the pipe entrance. Therefore, capacity is not a problem. [3] 36" CMP culvert along west side of Duvall Avenue N.E. - The slope is 1%, length is 80'. Capacity is 36.1 cfs flowing full, or 35 cfs with no headwater over the top of the pipe entrance. Therefore, capacity is not a problem. [4] 30"CMP culvert system through Windsor Place - The minimum slope is 0.8%. The capacity flowing full is 19.9 cfs. This is also listed as a flooding problem. While some headwater buildup would be necessary to convey the existing 100 year storm event, the reduced flow from the Orchards detention system should not be a capacity problem. There are some constrictions placed in the open channel, presumably by the property owner, leading to the culvert which may cause some v minor flooding, but nothing of concern. Specifically, a 12" pipe under a small trail would cause the flows to overtop the trail, but the flow would still be contained. [5] 12" and 18" culverts in rocked channel. - The Windsor Place plans show that these culverts were to be abandoned and the channel was to go through the existing access road. The road was to be blocked off. However, even if the flows must overtop the road due to culvert capacity problems, they would easily be contained within the immediate area of the swale. [6] 18" concrete culvert at the water pump house - The slope is approximately 2%. The capacity is 16.1 cfs. There will be a slight headwater buildup to convey the 100 year storm event, and the available headwater depth is more than adequate. [7] 36" concrete culvert crossing N.E. 4th Street - The slope is 0.5%. The capacity is 51 cfs flowing full. Capacity is not a problem. [8] Channel along N.E. 4th Street - This is also listed as being restricted by the Maplewood Drainage Basin Study. The study calls for reconstruction of the channel. Our field inspection verifies this observation. The channel has a negative slope of approximately 2' along 4th Street before it turns to the south. It has adequate depth but needs to be regraded. As it exists, it still has the capacity to convey the 100 year storm, but would likely cause water to back up though to the north side of N.E. 4th Street. In a City of Renton memo to Mary Lynn Myer from Randall Parsons, dated January 21, 1991, the drainage concerns above, along with erosion problems further downstream, were discussed. The recommendation was made to over-detain on the Orchards project for the 2-year storm (releasing at 50% of the existing 2-year peak flow rate) and for the 10-year storm (releasing at the existing 2-year peak flow rate). Additionally, the existing 100-year peak flow rate would have to be matched or decreased for the developed 100-year storm event. These criteria have been met or exceeded by this preliminary design for the Orchards project. • i Z Ds g ADDENDUM TO 22- -3 SUPPLEMENTAL 2 2 410 zz gy ENVIRONMENTAL IMPACT STATEMENT - � I for oEVE�ep��F �' THE ORCHARDS RESIDENTIAL DEVELOPMENT City of Renton Planning/Building/Public Works Department Prepared in Compliance with the State Environmental Policy Act of 1971 Chapter 43.21 Revised Code of Washington Date of Issue Prepared by: Dodds Engineers, Inc. 4205 148th Avenue N.E. Suite 200 Bellevue, WA 98007 (206) 885-7877 . � PREFACE This document is an Addendum to the 1982 Draft Environmental Impact Statement, Northward Rezone and Development and the 1991 Draft Supplemental Environmental Impact Statement, The Orchards Mixed Use Development. As described in the 1984 State Environmental Policy Act Rules, WAC 197-11-706, "... an Addendum is used to provide additional information of analysis that does not substantially change the analysis of significant impacts and alternatives in the existing document." The proposal described in this Addendum includes a portion of the residential acreage analyzed in the 1982 Draft EIS and 1991 Draft Supplemental EIS. Additional information and analysis is provided in this Addendum for the following elements of the environment; unique physical features, water (drainage), wetlands, transportation, schools, parks and recreation, sewer, and water supply. 95054A-1.DOC; 02/09/96; Page:l FACT SHEET This Addendum to the October 1982 Draft Environmental Impact Statement Northward Rezone and Development and the April 1991 Draft Supplemental Environmental Impact Statement, The Orchards Mixed Use Development has been prepared pursuant to the provisions set forth in WAC 197-11-600 and 197-11-625. PROJECT DESCRIPTION The proponent, Northward Properties, is proposing a residential development of 59 townhomes and 63 single family homes on an 18 acre site. The project's overall density would be 6.8 residential units per acre. Approximately 55 percent of the residential area would be retained in open space. The site is located in the northeast portion of the City of Renton, south of the intersection of Duvall Avenue NE and NE 6th Street. There are no structures currently on-site. Grading and clearing of most of the on-site vegetation has already taken place under a previous permit. Existing zoning on the site is R-24. RESPONSIBLE OFFICIAL Environmental Review Committee City of Renton Planning/Building/Public Works Department 200 Mill Avenue South Renton, WA 98055 Contact person for questions, comments and information: Jennifer Toth Henning Senior Planner Planning/Building/Public Works Department 200 Mill Avenue South Renton, WA 98055 (206) 235-2550 Permits and Approvals identified to date include: • Rezone - City of Renton • Site plan approval - City of Renton • Clearing and grading permits - City of Renton • Building permits - City of Renton 95054addendum.doc;02/26/96; Page:2 AUTHORS AND PRINCIPAL CONTRIBUTORS TO THIS ADDENDUM This Addendum was authored by Dodds Engineers, Inc., Bellevue, Washington, under the direction of the responsible official. Principal contributors to this document are identified below: Author/Contributor Resonsibility— Dodds Engineers, Inc. Drainage, Utilities 4205 148th Avenue NE, Suite 200 Bellevue, WA 98007 IES Associates Plants and Animals 1514 Muirhead Avenue (Wetlands) Olympia, WA 98502 The Transpo Group Transportation 14715 Bel-Red Road, Suite 100 Bellevue, WA 98007 Terra Associates Wetland Mitigation 12525 Willows Road, Suite 101 Kirkland, WA 98034 DATE OF ISSUE LOCATION OF ADDITIONAL DOCUMENTS AND BACKGROUND DATA Technical reports (i.e., transportation, wetlands and sewer studies), the October 1982 Draft and February 1983 Final Environmental Impact Statements, and background data (i.e., the Environmental Impact Checklist, the October 1989 Residential Development Application, the April 1991 Draft Supplemental EIS, the August 1991 Final Supplemental EIS and the November 1991 Mitigation Document), pertaining to this project are available at the following location: City of Renton Planning/Building/Public Works Department 200 Mill Avenue South Renton, WA 98055 ADDENDUM COST $ + tax. 95054A-1.DOC; 02/09/96; Page:3 BACKGROUND INFORMATION The environmental documents directly related to this proposal are listed in chronological order below. Draft Environmental Impact Statement Northward Rezone and Development City of Renton, October 1982 Final Environmental Impact Statement Northward Rezone and Development City of Renton, February 1983 Preliminary Geotechnical Engineering Study Geotech Consultants, Inc., May 1988 Expanded Environmental Checklist, Renton East City of Renton, June, 1989 Biological Evaluation, Wetlands Delineation and Wetland Enhancement Plan and Retention/Detention Pond Revegetation Plan IES Associates, June 1989 Storm Drainages Study, Renton East Dodds Engineers, Inc., June 1989 Traffic Impact Analysis for the Renton East Residential Development The Transpo Group, June 1989 The Orchards Supplemental Traffic Impact Analysis The Transpo Group, June 1989 The Orchards Residential Development Application Northward Properties, October, 1989 Sanitary Sewer Study for Interim Sewerage Improvements To Service "The Orchards" Development in East Renton Dodds Engineers, Inc., November 1989 The Preliminary Design Report for the Upper Heather Downs Basin to the Lower Maplewood Basin Dodds Engineers, Inc., May 1990 95054A-1.DOC,02/09/96, Page:4 Draft Supplemental Environmental Impact Statement The Orchards Mixed Use Development City of Renton, April 1991 Final Supplemental Environmental Impact Statement The Orchards Mixed Use Development City of Renton, August 1991 Mitigation Document The Orchards Mixed Use Development City of Renton, November 1991 Wetland Mitigation Plan The Orchards Terra Associates, April 13, 1994 These documents are available for review at the following location: City of Renton Planning/Building/Public Works Department 200 Mill Avenue South Renton, WA 98055 95054A-1,DOC; 02/09/96; Page:5. CHAPTER I ELEMENTS OF THE ENVIRONMENT Since the 1982 DEIS and FEIS were issued, the State Environmental Protection Act (SEPA) has undergone revisions. These revisions were intended to reduce paperwork, publication and delay; simplify the rules and increase certainty; and improve environmental decision-making, including public involvement. This Addendum was prepared according to the April 4, 1984 SEPA rules identified in Chapter 197-11 WAC. Tile following list of elements of the environment marked "reviewed" are discussed in this Addendum. These items were identified by the City of Renton as key elements most affected by changes in the proposal since preparation of the 1982 DEIS/FEIS , the 1991 Draft Supplemental EIS and 1991 Final Supplemental EIS. Elements marked "not reviewed" have impacts determined by the City of Renton to be non-significant or unchanged from earlier proposals and analyses for the reasons briefly stated. I. Natural Environment A. Earth 1. Geology Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 2. Soils Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS 3. Topography Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS 4. Unique physical Reviewed in this Addendum. features 5. Erosion/enlargement Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS B. Air 1. Air Quality Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 95054A—t.DOC; 02/09/96; Page:6 2. Odor Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 3. Climate Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS C. Water 1. Surface water Reviewed in this Addendum. Movement/quantity/ quality 2. Runoff/absorption Reviewed in this Addendum. 3. Floods Not reviewed; not applicable to site. 4. Ground water move- Not reviewed; proposal not expected to generate ment/quantity/ significant impacts beyond those described in the quality 1982 DEIS and 1991 DSEIS. 5. Public water Not reviewed; proposal not expected to generate supply significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. D. Plants and Animals 1. Habitat Reviewed in this Addendum. 2. Unique Species Not reviewed; none reasonably expected to exist on-site. 3. Fish or wildlife Not reviewed; not applicable to site. Migration routes E. Energy and Natural Resources 1. Amount required/ Not reviewed; proposal not expected to generate rate of use/ significant impacts beyond those described in the 1982 efficiency DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 2. Source/availability Not reviewed; proposal not expected to generate rate of use/ significant impacts beyond those described in the 1982 efficiency DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 95054A-1.DOC; 02/09/96, Pagc:7 3. Nonrenewable Not reviewed; proposal not expected to generate resources significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 4. Conservation and Not reviewed; proposal not expected to generate renewable resources significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. 5. Scenic resources Not reviewed; addressed under AESTHETICS section in June, 1989 Expanded Environmental Checklist. II. Built Environment A. Environmental Health 1. Noise Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 2. Risk of explosion Not reviewed; proposal not expected to generate significant impacts. 3. Releases or potential Not reviewed; no releases likely. releases to the envir- onment affecting public health, such as toxic or hazardous materials B. Land and Shoreline Use 1. Relationship to exist- Reviewed in this Addendum. ing land use plans and to estimated population 2. Housing Reviewed in this Addendum. 3. Light and glare Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 4. Aesthetics Not reviewed; addressed under AESTHETICS section in June 1989 Environmental Checklist. 5. Recreation Reviewed in this Addendum. 6. Historic and cultural Not reviewed; proposal not expected to generate preservation. significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 7. Agricultural crops Not reviewed; not applicable to site. 95054A-1.DOC; 02/09/96; Page:8 C. Transportation 1. Transportation Reviewed in this Addendum. systems 2. Vehicular traffic. Reviewed in this Addendum. 3. Waterborne, rail, Not reviewed; not applicable to use on-site and air traffic 4. Parking Reviewed in this Addendum. 5. Movement/circula- Reviewed in this Addendum. tion of people or goods 6. Traffic hazards Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. D. Public Services and Utilities 1. Fire Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. Mitigation measures established in 1991 Mitigation Document for The Orchards. 2. Police Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS, June 1989 Expanded Environmental Checklist, and 1991 DSEIS. Mitigation measures established in 1991 Mitigation Document for The Orchards. 3. Schools Reviewed in this Addendum. 4. Parks or other Reviewed in this Addendum. recreational facilities 5. Maintenance Not reviewed; proposal's impacts expected to be typical of new buildings. 6. Communications Not reviewed; proposal not expected to generate significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 7. Water/Stormwater Reviewed in this Addendum. 8. Sewer/Solid Waste Reviewed in this Addendum. 9. Other governmental Not reviewed; proposal not expected to generate services or utilities significant impacts beyond those described in the 1982 DEIS and 1991 DSEIS. 95054A-1.DOC;02/09/96; Page:9 CHAPTER 2 DESCRIPTION OF PROPOSED ACTION INTRODUCTION This Chapter contains a description of the proposed action, and a history of development proposals for the site since the 1991 Supplemental EIS. Chapter 3 provides a detailed description of key elements of the affected environment, as well as the environmental impacts, mitigating measures, and significant unavoidable adverse impacts of the project. NAME OF PROPOSAL AND SPONSOR The name of the proposal is The Orchards Sector E/F and G. The project sponsor is Northward Properties located in 1560 - 140th Avenue N.E., Suite 100, Bellevue, WA 98005. PROJECT LOCATION The 18 acre site is located in northeast Renton, south of the intersection of Duvall Avenue NE and the right-of-way of NE 6th Street. The site is located in Section 10, Township 23 N., Range 5E, W.M. See Figure 1 and Figure 2. PROJECT HISTORY In 1982, the Draft Environmental Impact Statement, Northward Rezone and Development was issued followed by a Supplemental EIS in October 1991. The Supplemental EIS addressed the proposal for a site approximately 62 acres in size, which included all of the residential acreage identified as the current site in this Addendum. Table 1 Comparison of 1991 and 1996 Proposals Acres 1991 Proposed Action 1991 Alternative 2 1996 Addendum Single-family 0 0 18.0 Multifamily 15.9 13.3 0 Office/Comm. 2.1 4.7 0 Total 18.0 Ac. 18.0 Ac. 18.0 Ac. 95054A-1.DOC; 02/09/96; Page:10 BOTHELL POULSBO 5 REDMOND BELLEVUE o S AT LE LAKE ' J�1 •,WASHINGTON BREMERTON PORT ORCHARD ISSAQUAH 900 1-405 �.6 SITE 16 160 99 :' RENTON VASHON 167 to ISLAND .161 MAURY> KENT ISLAND GIG HARBOR 5t6 co FEDERAL AUBURN y; WAY 9� F4 Fy 169 FOX-. 16 167 ISLAND 99 161 'MCNEIL 167 : 'ti PPS E' l, Is TACOMA SUMNER 16.E A" BONNEY LAKE DERSON LAKEWOOD ISLAND PUYALLUP 512 Ja Al BUCKLEY 162 N 507 7 REGIONAL CONTEXT FIGURE 1 G-lb-1 te,f, soiAc SEC.m oU' � A(F) �3 4 > *4 .1 Qv' q m C. (14' ......... X pST 1 E. I I S—T IT 01 " —1—j b—d. s'. 4AA At j 014 C Z , 8 .@ 9 1 Ac. F, ml- 51.W— ffilr— A uj :1 S'.."oi­s"AC" o 654., 1.1sh 3 Sp ?009 dUA, l6 AC it) t s- 6 1 A."' 0 61 A,. c• Bernis Craig ui > w cl > ejl 01 01 2. c w.11—, sr-Rc ZAC e Sh Ac t A M -/7/r-/�/ - --at% 5111 S T. A�j tqv 1-f r te I w > it Mr.r. lEnitAG(r.: i Ej_ f,,AC. FO 6 A 4 uj I o"AC 0 z u nl a oth C 4.40 Ac d t! • uj _Tr_ > c C. AA) _wm uj LJ. c C Ac a. a. C), D cb > i 4�Z, 1 (n 3: , - 1 2 3 0 c E E T 2 D. "r 7 E4:aE7F,,52imjZq)'H_.. Ly :7 q3 4 0:1 q - ;e 4 1. w E w" 51 t 121 R." 1 > I j,Ac. slio Sot r j 131 r . , a, o') N0 .........I C m,.ss-1 4 W.Ac S A CRE T 1 1.11 AC. 474A. p....0 B.swo 1 sr P13611 A, LOCATION MAP CC 0 z FIGURE 2 SEC, 10 TWP. 23 N• RGE 5 E. W.M. C �w _ �_ ►e and 4TIQ7 = ._, - -. - _-- -_ --_ -.-'' € --_.-�- eaee[C,Tm c•I..n3 s� I �!I r-.t[ r, �. .o "•e.J} 'is 3 _„-. tl - MM'Iy I �� TR.00T B e.s - I �I i � ',I b " i « I I I I I I � _� �---1 �~ ^IY� � I � 1 :- .'—�• � <9 � r— __ u. 24 71 I �' aT - - _e�.e�b ) I' r� o• � - �--- I L.es.« I I ,•,e«� 'i.ay«`_ � I I I 19( �\ '�\ `�-� _ � I _. 44 I l;' I •� � I r-.- + Lea--� I II ' M I\ �ses� ) � 1 s T �� �� 9 i xx. : i xr1l rJ .t TRACT A .r v .� j' are.. 5? gi >'•+s xe�e« I OMW tx tet t. '•Ps1 xM• < �z I 3 . -- bl I 9•�' rL-Te-_J ` I I r.w..r ..a5o o n /V` Ii ' xe « f ---- i{ ,,I----�--J �;' � I• � � /; I r-.----� f- ,�r--- � UZ a i7 r I � � � �.•.• � � T=--xtr« � � � Y I- « A I I I �1' \ �j e `t_- �' - , I 51 1 II TSLi N I I 'I 1,_` Z 'to �yWa I o _ L- •r-J �' l si _� I i a►ai«�� I I I F / \�f y I I _ Tw II , 1•r r (.. irz Z S , r---r % 7O e• � I L s.-r� I I � I s C � I : •r � .r I, W} y • 99 '_� I W> t ; . � o ea+. -- `� 1 " Te ee i r. d• I � -�D-�::P.'Js ' � -� � 30 •t nse��e: V y _ 7•AE xJIU I I I �:Y L 1 i ti ` 1RAC7D_ 7-- -•, O o $ MOTE EMth w x.s..a r +4 I ».ej. I _ •I I I3 ` ♦ �i ) Z? A,. m ME te� Q�; 1 1/ 1 I I ? I 1 _^ - ^ I 1, Ii, I iy t .. ` r ) xss.. { C d --� $ I & I J I L 10 - I WW Trr OrWnd••Dly 2 -°F- = I - I I i I I I 1� W -x- - ',r - 3-1«__ I 'r o / '� r --n--�- _ r--r-1 I I I 'I ' 1r"1•r p n. II O Ral lc�LE.r� , M1 -- I 1 I I I tC aw I 1 Q LI -a'—J' r1 r 1 rum // �\1\R7 r I w 4 I I.� I I +r \ I r r xo•r 1 w I p W e•.e sr..rre —•--�� se% I I I 1 I i-'T 1 L_— _�__J I Wnrr/� 1 I l .� _ 33 i i OJ DU I i ` I w(j i 1 39•_G 140 i I <I � 14Z I ' µ�l I � l 1 «- I ^ x, I' �--7 � I ' �•/ • µ ` --_ I �.Lis ,i- ( r I Tsui.r� Imr•rl I '37s r' Kites Ir L -�+ —.1 R ��b � I � � �` � • - 6 `J .tJ �_ I •II I Y I f7-�r ,• - L xu J ilf 1 _+� asr r ssr•rl �/ •�• _ _ y . �/ n � Q I ,l� I I Q TRACT F 4" k —_ v t r »se«.1' cam'''ecrcw yypp .�,yo »emu •ri 1 tteuo..rcr '+ <� fe ,� a 19 I ve h roe�•r To 41 ?9 r "S 20 I!7ss-•r_— xev.r i t xu•r I xe�.r . I I 6 i I 1 n I 8 I 9 I i t i ! -aerL,w / r eas•r '♦ -1 O �' _J L---J xev•r I 1 1 - f r I d L _J L-_-J xe:=.J L xu•r J I xu r 2"5 cc L-s-•. f I�.ecs•r�? WJ« i .•� I' / J,.� ._� ?) L__ ,t, r.f _ ._. .o.ar - - -I --`_ -Sr- _ ?? ?3 ?4 I a `V ?Oh t' 2b- ?l.^ 28 I _ mp • I�t. // -- b•t•-' �T IJ, I ::-j,/ G //'��T p -- -- ---J L vsre.r t�✓ tra• i O o. V .......... ... _ ., I `� '� J�li I �f� \ rY°'07Tw II Mcml• .. �_ _- ---J t O k O iE 3 Z 41I Q kZ SECTORS LEGAL DESCRIPTION SECT � 'K O �m _ r a= 0 ttr beuth trlf d tt.e Me^ttseet nuen.r d the 6wntren cr..rtrr d the ba+Ue.eet q.•ertr d°..etion IO,T .e Eeet,WP'Lr EXCEPT Ur Etit 42 F- �'�73 Muth tlenoe° e ronv�jed by fired-4-b•d uetir ►g Mo.H °E e• ner/DeVClO Cr V41 K trn eT TMe Manh tylr d this p Ene ineer/Planner/Surveuor er the ` 4 v-d the°euUreat 4�e•tM Ma•tr.rd Pfc w%bmoetYf.Eroliwe,Inc (/� tb.rurrt 9+•''t�d beetlan 10,To.n•tyP 2!NCrNt tbnoe 6 � +MA 4Mn A-ME < Y E•.r`rWSO" 1 I0 E,Cov+y Eby a..�a O d��°E.. to K ��7t�O K 1Olu eT ' 64ri.yq ALSO EXCEPT thrt PcrUon d ME•tn°tr.�c M p�tt�d ti C �r`d GIMy lb"o't.f. WA eOCn teecerde,g No 116 I.7! 9.=l rr volwe IV d P'Wr, , T-1(206)1tl.rQ4 A7A S �y Ge�g Knwo�-Plernr � � ' (2C6) b�..y,PLA „w SIT a 'K �10 T.I.L�C3AL DESCRIPTION 6ECTORS G ti r or tr,Mo•t,.wt V m �I< or this 6.,.h-t 4✓••�d V.r n q..ertt SCALE 1 = 50' E..t Wr1 ExcErr w 2 b.T f f- 73 NA. Rr�6 STATISTICAL Sl1MMAR1' Q '� ti nu er w tttr.,er rrx T!!th Arse°E ee 2 C!f W risen• ene u .y7C��e..e r•eore.d.nder teeeory 25 °� _-' Ttr MwV+heV t+a•+,rn 4WD d tti No. Teal Ary CTOItPb .F lECTp1¢G TOTAL Z Z O t I¢d ttr°antert 4r^�d F.ctbn tO,T °o21 .t 4rrr !E•rOp e9,R/°d!•tree M AU ec,,rL r to•c.e 1MD36 W,ti/t°GO ea ee � n < 4 �' EMI.Wt1 EXCEPT thlr ttt•et 47 INt ��7!MorVt R..r}6 P-P---d M.bo d L." r! V'•--f la l!!th A.+.om er M 8'EaYtrg/Armed R-2• R-74 122 < I!I J Ca^�j tTj sa..d r�eo.00d vrar w.00ra.,g Me. °his Ganr.9er O OW O a VICINITY MAP w.et Armor. Clwoc of.(lo.00%.ar E r) -%Epp of.rt°GOf.d GJ Kern.f(7uK •d total u) SMc E T i OF Mo. FIGURE 3 = >ro 495054 rME CfiGMAlme ' _ �0�4tIPR. K a.ru!T. _ - - •; �.!v Tc[.r ry.-tw;.r r �J R3CIO J I. Tft SKLTERI kip i •- I ��,\� v wmo 4•.I1,?Er-ILE+7•¢Ot ORCWA __ v -e:cw6 N'e':aw10�+•Cr- - - ` T RDSa � -eFc- ietlw`-Efi.G.I'law5 \ SECTORS E f R1' - PaaK- C _ JW -- _ • WAGS NGTON OMN ei+dCE Q •I l.• I Xf�' 1bE"L�Jp � .� _._. . FEGST� 1••�» • Z F LN••C..Y.4�+i;r;047`ECT • J I c r :If:K LINIIFi�G1L.',cb�- 1 , I < Few cj8s..[1 Nb/fi a''Ot title uwv t ." I J / •I - I c TORAH^$ 'rLs Lr,10 7 K TLP-ME!n!f ! T>TM+•uc r1/•.r�uJ66 rrcR 7pZRe. t :�.•�. ^61set:I••'ES �• \\\ I I � 1�11f•Iµ 1 E, ALLLry LMITS 4;F� < 1 f i 1 ,�,?�t•I a i A rim' J�P�a•��-J O y ? ;h I• x� 4m. : Jos r_ T,t-t�L„ ! �• O C�O>NC.TCN �. 1•�•4�`�� / �'.L.{, , � O a� ... New �.vCC,!e",v.aos�'L -- � _ I • r!- "r � - � C '-it � '_ - r.rrsc.vsuc;,,�aG.Ta• - _� 4 p ScCTORS E J wPLATTEC .� �►facet ewe . N� Pr-Via. ��,�6.- ME PRELIMINARY LANDSCAPE SCHEDULE Li'1� '\1��" p I �1�1D � \ li� t�1 Scale r 50 VMB L BOTANICAL NAME COMMON NAME SIZE 6 CONDITIION SYMBOL BOTANICAL NAME COMMON NAME SIZ Dale E 8 CONDITIION 26/95 Deciduous Trees- medium/large n,n 1-31.•"[,IC-r< cm I Large Shrubs -n -:r --acaac Dawn By � A. p.•..dopuurw 5yeemor.`hot. a.tl brencn•d..v.nhj L - o Coeorw.sc'.ae:ew Pern.y C,;aonee•eer ry'___-•� sa*a• ^nsefiner ne'ikZC�v M4W •.oar rub.aan'Rd 9ur..•n R.d 5---Aw. -...a o.a.5-ll.t, P.erbar l•UKP Wn.P.m�arber•y • � �� - •ed Z.�tov-a•.nau 5-1-1 Z.— E.,onpnu•ala:w ompecu uJing.d 5cra�eou>n O'. Accent Deciduous Trees- flowering/fruiting rnn.e•M_.,,Iu-o-v..o Rrodod.r.�on>o. Rhododar Jron Fev5�r5. Pt.rl•no-lbv.da Pl.rl• A—.,,.,usun Fn.napu ureil-orenU.w.D.O Metu nano..Ie acwrorun Tell C•.Pb=Grace Q nal •Pp. Flou..ring Gaoappl.Baro1.4opi. ' Cor•w`—. Ka.an Doauwoa Small Shrubs - - _••- -- -a,a Pv.u••pp, fl-11l q ,S1111r.g C++-y-rs.. / /, eb.ua g.'Eou.erd Goucrvr E-ara Ga.cru: r°'• -"� '-•D' =^inner Narrow Deciduous Trees rnn.1_I/-••ul,a'r.a- Daro.ru krona Cu,arr J.—c a O .+c.r ryyaaa Colunrur R.o•naDi. w.11-brancr,.d.D•6 Rhodcd��dra..PP. Lou,Rhod«,orcn> .G:e'aaa __ •_�_ _ e Ptlu•ull.ryaN 'R.d•p�r. IR.d•P v.flor.�u,g Pear II..er•.�eu Ce.noeeea' Ge.noees:aoane•e-e�y Ju.lp.rw•p. Jv.1p.r Evergreen Trees '•+1n 5'-6'na till a zT..r., Phs,..•,go"ugo T na,go Plne h�a pur_au uYuarn ROP C.aar so Pu..515 Poaanu ua rru,uce.a y.vcby C.—rc Pns,.nlgra A­.­P�•.. P,.uooa•..ga•.�.z1«u Doagla.•v r ! Oroundcover d Accents .- - �•x ® Accent Evergreen Trees r1n e•Im•k•o.c�..w �//j// -->_,,, ,+- 9.q—,a I u.su Glans Ncso•uPrylo>�r'a-w.I KI..uOumlc. ca . ae'oc 99 3.Puou rWI so oars DaD Co,o...a•sar da— Lou,Cosan.en.r �- C.orw d.odara D.odara Cwar Iuyparlc,an ulyc:nw. wyp.rlcsn P•.•aoa•uCja+>.r.z1..II Dougu•fv hnlp•.ar.p. an�Dr lawn and Rough Orau - FIGURE 5 st"p'''t� . i yun,Wuyl Wn'��rr /I-;U( �uI; � �`iI,��_a4Ai uRlI rr- - -as - - -- —al m�'so� _ m�li ppl l c.::f.•::!., �q0 V minul 8� l uF - aEBFWMRTCN AVE �xIII lII lo 44 -�-- TCFJ 1 I I r i f V' � �q� •On s � W \ / m A Q f ,Ls-Ij Ul 11 m ' O m p PUBLIC w ' 6 PUBLIC ALLEY �L,L. - I II II I _ W � II I co 15 Am 'Za2 u I,no � �- - -OPEN SPACETW --,,I v--1 - --- - - u I I� lot N I „ $ r - ,•— -- DWALL AVE NE I I I I Y to 8 4 N O � i muKaat Z � a iizu —I a � � m0 �2 pZy� � �� m i Z''�� �Trb� m �A , t,J� �� Y '� �QE• Q E � ' 3 V.O, AK 'K Z o qgiZ iS �' 07 �g L z 1, oarE ✓.INUAar 1996_ pREL/M/NARY GRADING & UT/LIT/ES PLAN DODDS ENGINEERS, INC. ---- '^ DESIGNED fT. JCNES pRcLIYIN,4RYPUTSECTORSE6f-TNEORCHARDS CIVIL ENGINEERING SURVEYING PLANNING - th n " DRAWN ILK, LRB 4205-145TH AVE. N.E.— SUITE 200 #; APPROVED_ NORTHWARD PROPERTIES40 BELLEVUE, WASHINGTON 98007 U 1 I- m __ U4Alo KRUEGER 1560 — 1401N Alf. N.E., SEVE 100 A vao�cc? UANAGF.R 8£LL£WE, WA 96005 (208J EES-7E77 I•u•9v i N - Ott DUVALL AVE HE - u 'Z� IPA m / i n- i �' m N(l 8 Alp I tj Y �m �1 • _ �' ' f N ; W 1 ' — N -N ^m 41 to 1-4 Lu \ � _ J' I N UI w W _ W A ,: m lD � � .. J �� •N _ V1 m I I I I N o t o Lo ZOAli r „sy .lr _. U w o mayAVU Na la "' �_ . pQm 70 8 o a Aye Jul Jul N c � q - o �. m Q 0 V N DALE JANUARY 1996 PRELIM/NARY GRADING A UrILIrIES PLANN&L DATE ° v m DESICNEDE.r ✓cwcs DODDS ENGINEERS INC. ` T.j �,� O1 -------' CIVIL ENGINEERING SURVEYING PLANNING DRAWN TZK /RB __ PREumARYPUT SECTOR q-mE ORCHARDS ---_ - NORTHWARD PROPERT/ES 4205-118TH AVE, N.E.— SUITE 200(�z APPROVED _ — m r BELLEVUE, WASHINGTON 98007 CRA/C KR_U£GY-R /560 - 140TN Al�£. ME, S!1/lE /00 _ • n PwoJECI MANAGER OIL BL-W-WE, WA 98005 1206)885-7877 I.299�a A r JJ � I I I II � JJ J JJ 4 C rn - 00 NORTHWARD T H E ORCHARDS ISLO NOth AVE. NE I I BELLEVUE. WA 1800-1 (200 741-12c RENTON, WASHINGTON JJJ yl III i I J �u III' J� J , i III . �lid now' JJJ II���9 NORTHWARD A THE ORCHARDS C� +1 �. onnaw nn••• :� Iry � Inillllll� � �� J'`, ,`•••I ` II I '9 INR,�;.y��iII�II�II I �� III�II��............ �I�IIIIII�IIIIIII�%,a i�\,/ $3"" �Illillllllll ��/' � IS I�'� 1 tlIIIIIIIIIIIIIHflIIIINI� �,�IIIU IUllll�l/,. annlllllllinllll@`I � '� 'Yias'U,icss3$1lYry ,�II'If,.�. �./✓�•R.�i�� ` II II`I�`� II /IirS//'rl iyil Wes• � '� {� �• r/i/S�r�/�:i. ,yn ( • 4411++11!!``\\�^'I m�II i ��a�4: i..fLl,Giilii7 r'S�n i•If � ! • The proposal in the 1991 Draft Supplemental EIS requested a rezone of the 18 acre site from the existing G-1 zone to a mix of R-3 and B-1. The objectives of this proposal were to develop a mixed-use development, including a community commercial area, office uses, and multifamily residential uses. Two alternative conceptual site plans were presented and analyzed. The proposed action included construction of 212 low to medium density multifamily dwelling units and 28,000 square feet of commercial and office space. Alternative 2 called for construction of 131 low to medium density multifamily dwelling units, 124 townhouses, and 70,000 square feet of office-oriented commercial area. Alternative 3 did not include Sectors E/F and G. The site plan addressed in this Addendum is similar to the site plans for the proposed action and Alternative 2 in the 1991 Draft Supplemental EIS in that the acreage of the current site corresponds to that portion of those alternatives targeted for development. The City of Renton has determined that an Addendum to the 1991 DSEIS, The Orchards Mixed Use Development should be prepared. This decision was based on the SEPA Rules (April, 1984), which indicate that, "...an Addendum is used to provide additional information and analysis that does not substantially change the analysis of significant impacts and alternatives in the existing document (WAC 197-11-706). The rules allow an agency to, "...use environmental documents that have been previously prepared in order to evaluate proposed actions, alternatives or environmental impacts". The rules also provide that, "the proposal may be the same as, or different than, those analyzed in the existing documents" (WAC 197-11-600). According to the procedures regarding Addendums, this document will be distributed to all recipients of the 1991 Draft SEIS. PROPOSED ACTION The proposed action is for the site plan approvals, preliminary plat and filling, grading and building permits for the implementation of a middle-income, single-family and townhouse residential development in northeast Renton in an area known as the Renton Highlands. The proposed development, The Orchards Sectors E/F, includes preliminary platting of 63 single- family lots and 59 townhouses. Separate access would be provided to the townhouse and single- family areas, with no interconnection. Assuming 2.0 persons for single-family unit and 1:5 persons per townhouse, the anticipated population of the development is 215. The site is currently vacant and cleared, except for the wetland and buffers in Sector G. Immediately to the west of the site is the 202-unit Windsor Apartments. North of the site, east of Duvall Avenue, is a proposed 200-unit multifamily residential development called Forrest Crest. Also to the north are Sectors A, B and C of The Orchards with single family homes and townhouse condominiums. The land to the south is zoned for commercial development. 95054addendwn.doc; 02/26/96; Page:l 1 Building Development The Comprehensive Plan designates Sectors E/F and G to be Planned Neighborhood Residential with a zoning designation of R-24. The site areas and coverage calculations are as follows: Sectors E/F Sector G Net Site Area 366,208 s.f. (8.4 ac.) Net Site Area 399,428 (9.2 ac.) Building Coverage 83,000 s.f. 23% Building Coverage 83,000 21% Public Street 63,300 s.f. 17% Private Streets 46,300 12% Drives & Walkway 27,500 s.f. 8% Driveways/Walkways 23,500 6% Common Open Space 41,700 s.f. 11% Common Open Space 171,200 42% Private Open Space 150,708 s.f. 41% Private Open Space 75,428 19% Total: 366,208 s.f. 100% Total: 399,428 100% The gross density for Sectors E/F is 7.5 du/acre, with a net density of 11.7 du/acre. The gross density for Sector G is 6.4 du/acre, while the net density is 15.9 du/acre. Vehicular/Pedestrian Access and Parking There are two points of access into Sectors E/F, one from Bremerton Avenue N.E. and another from N.E. 6th Street, which focuses onto the landscaped private park. A series of grid streets and alleys then provide access to the homes. The streets have been designed to provide street trees on both sides with 8 foot deep planter islands and sidewalks on one side and a landscape strip on the other side. There are landscaped "neckdowns" at the intersections to reduce the hard surface and to provide a tree canopy. There are also landscaped areas at the entries and along both Duvall Avenue N.E. and N.E. 6th Street to create an attractive streetscape along the edges. The sidewalk along Bremerton Avenue N.E. has been attached to the curb to create a landscape area within the street right-of-way. The traditional homes will include an attached two car garage with additional parking on the garage apron. The cottage homes (alley accessed) will include an attached two car garage. Guest parking will be provided on the internal public streets. The total number of parking spaces is as follows: Traditional homes garage spaces - 76 Traditional homes garage aprons - 76 Cottage homes garage spaces - 50 On street guest parking spaces - 37 Total - 239 (3.8 per d.u.) 95054A-1.DOC; 02/09/96; Page:12 The concept for Sector G (east of Duvall Ave. N.E. and south of N.E. 6th if extended) is to provide 59 for-sale attached townhomes on fee simple lots, accessed by way of a private street system. The townhomes are accessed by a private drive that aligns with N.E. 6th Street on the west side of Duvall Avenue N.E. The private drive (with gated entry) crosses a narrow extension of the on-site wetlands then proceeds to loop through the townhouse neighborhood and terminates in a landscaped cul-de-sac. An emergency vehicle access lane is provided at the southwest corner of the site per the previously approved plans. A series of landscaped pockets have been placed along the internal private drives to create an attractive streetscape. The townhomes are both one and two story in height with attached one or two car garages. Guest parking is provided throughout the site in parking bays, resulting in the following parking tabulation: Garage spaces - 89 (assume 50% 1 car, 50% 2 car) Aprons - 96 Guest parking - 14 Total - 199 (3.4 per d.u.) The townhomes in Sector G will require the improvement of Duvall Avenue N.E. along the frontage, with no additional public road or transportation improvements. Site Utilities and Site Preparation The utilities for this proposal are all available through the extension of existing services. Water and sewer mains have been installed in the adjoining streets as part of the overall development of The Orchards. The sites have been cleared previously as part of The Orchards development, except for the wetland and wetland buffers in Sector G. Earthwork calculations for the site show approximately 67,000 cubic yards of fill. A filling and grading permit from the city would be required. Building Orientation, Heights and Materials The concept for Sectors E/F (bounded by Duvall Avenue N.E., N.E. 6th Street and Bremerton Ave. N.E.) is to create a neo-traditional neighborhood with a total of 63 traditional and cottage homes, focusing on a small private park. The traditional homes are situated on lots that are approximately 50 feet wide and 73 deep (±3650 s.f.) with garage access from the internal public street. The cottage homes are accessed by way of a public alley with their entry facing toward the public street. The lots are approximately 37 feet wide and 87 feet deep (3200 s. f.). The intent is to create an attractive streetscape by reducing the visual impact of the garage through alley access for the cottage homes and through the garage placement of the traditional homes. The streetscape will focus on the front doors and porches of the homes instead of the garages. The building heights will not exceed 35 feet and building materials will include wood, hardboard and/or masonry exteriors with cedar shake or asphalt shingle roofs. 95054addendum.doc; 02/26/96; Page:13 The homes will be two story in height and will transition down along the street to provide the appropriate residential scale and massing. Both the traditional homes and cottage homes are designed as "zero lot line" homes where useable side yards are created through reciprocal use easements. In this way, the resident will still have private yards on the smaller lots. The concept for Sector G (east of Duvall Ave. N.E. and south of N.E. 6th if extended) is to provide 59 for-sale attached townhomes on fee simple lots, accessed by way of a private street system. The townhomes are both one and two story in height with attached one or two car garages. As with the single family homes in Sector E/F, the massing of the townhomes will transition down to the street at the ends of the buildings to provide an appropriate scale to the buildings. The number of townhomes in each building varies from two to four per structure to provide variety along the street and along the edges. The townhomes have been designed to fit the contours of the site and to focus onto the large wetland adjacent to Duvall Avenue N.E. The building heights will not exceed 35 feet. Building materials will be similar to the homes in Sectors E/F. CONSTRUCTION SCHEDULE Construction is planned to commence in 1996, with occupancy slated for 1997. 95054A-1.DOC;02/09/96; Page:14 CHAPTER3 AFFECTED ENVIRONMENT, ENVIRONMENTAL IMPACTS, MITIGATING MEASURES, AND SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS This Chapter describes the affected environment, environmental impacts of the proposed action, relevant mitigating measures and any significant unavoidable adverse impacts to the environment anticipated as a result of the proposal. For each element of the environment analyzed in this Addendum, potential impacts of the proposed action are discussed. Mitigating measures are included and will be considered as part of the decision-making process for this proposal. The following environmental elements were identified by the City of Renton as key elements most affected by changed to the proposal since preparation of the 1991 DSEIS. Elements which were not reviewed were determined by the City to be nonsignificant or unchanged from earlier proposals and analysis. WATER This section summarizes the storm drainage study for the project prepared by Dodds Engineers, Inc., in June 1989. Their report is included as Appendix C to the June 1989 Expanded Environmental Checklist for the Renton East Residential Development. For further information on soils, geology, water absorption and groundwater, refer to the EARTH and WATER sections of the 1982 DEIS. These specific topics are not addressed in this Addendum, since it has been determined that there would be no significant change in impacts between the analysis presented for the 1982 DEIS proposal and those which will result from the current proposal. The particular issue of storm drainage is addressed in this Addendum, since the current proposal presents a similar approach to storm drainage control as described in the 1991 DSEIS. Under the present proposal, the existing on-site wetland is enlarged and used as part of the storm drainage plan. Refer to WETLANDS section of this Addendum for more information on the existing wetland and proposed wetland enhancement program. AFFECTED ENVIRONMENT The project site is located within Zone 2 of the City of Renton's proposed Aquifer Protection Area (APA), according to revision No. 9 to the Aquifer Protection Ordinance, dated March 14, 1988. The intention of this ordinance is to protect the quality of the groundwater in the aquifer used by the City of Renton water supply wells. The ordinance disallows the storage or production of regulated compounds in certain areas of the APA. The APA encompasses the recharge area for a well or well field. Each APA may be divided into two zones, each with a different level of protection. For a well or well field, Zone 1 is defined as the area between the well or well field and the one-year groundwater travel time contour. Areas in Zone I generally require greater protection. Zone 2, the zone in which the site is located, is defined as the area between the one-year travel time contour and the boundary of the APA and encompasses upland areas north and south of the Cedar River Valley that contribute recharge to the Cedar River. Areas in Zone 2 generally required somewhat less protection. Residential uses are permitted in Zone 2, with connection to a central sewer system. 95054A-1.DOC; 02/09/96; Page:15 Sectors E/F and G are located in the easterly drainage basin for The Orchards. ENVIRONIv1ENTAL IMPACTS The proposal would convert about 41.7 percent of the residential area to impervious surfaces, such as roads, buildings and parking areas. Most of the on-site vegetation has been cleared to accommodate this development. This amount of impervious surfacing would decrease the amount of absorption and time of concentration, thus producing more runoff. This increased runoff could cause increased erosion and sedimentation and flooding conditions downstream without detention. Existing drainage patterns on-site would be modified with the proposed grading and the construction of the storm control system, including catch basins, conveyance piping and oil/water separators. On-site drainage facilities have been designed to accommodate both a 25-year storm event and a 5-year release rate and a 100-year storm event with a 100-year release rate. The proposal would change the character and quality of stormwater runoff. During construction, silt and other sediments could be washed from the site downstream without an effective, comprehensive sedimentation and erosion control program. Various construction materials and chemicals, such as oils, wet concrete, tar, wood preservations and paints and solvents could also enter the site's stormwater runoff and flow downstream. Following development the runoff would contain higher concentrations of phosphates, nitrates, heavy metals, oil and grease than in the natural state. Although the stormwater drainage system would be designed to trap and break down these pollutants, some water quality impacts are anticipated. No on-site storage or production of regulated compounds is planned, as described in the Aquifer Protection Ordinance. Tile stormwater runoff entering the soil may contain small quantities of nitrates, phosphates, heavy metals, soils, and greases washed from paved surfaces. However, levels of these pollutants are expected to be low and have no significant effect on groundwater quality. The project would be connected to the City of Renton sewer system via tight sewer lines and leakage of these lines would be very unlikely. Runoff from Sectors E/F would be collected in catch basins and piped to oil/water separators prior to discharge. The runoff will be routed through a grass-lined biofiltration swale. (The runoff from the off-site drainage in this basin, bypasses the storm drainage system in Sectors E/F and G through a separate tight lined drainage system). Discharge from Sectors E/F and G would be directed to the enhanced wetland area in the southwestern corner of Sector G that would double as a stormwater retention and treatment basin. The existing wetland on the site is fed and supported by surface water runoff. The loss of storm water or surface water through the development of the proposal would eliminate the only water source available to the wetland short of drilling and pumping well water to support this wetland. The livelihood of the two wetlands is dependent on maintaining clean, but semi-nutrient loaded surface water during the winter months and from intermittent summer rains. Use of sterile or nutrient free well water would reduce nutrients loading to the wetland with the potential of long- 95054addenduni.doc;02/26/96; Page:16 term depletion of sufficient nutrient for proper growth, particularly on emergent plants and larger trees. Studies have demonstrated that surface water treatment through biofiltration channels meet or exceed surface water removal expectations if the water is retained over a distance of 200 linear feet and the slope is no greater than 2 to 3 percent. The biofiltration swales on the site were designed to provide treatment prior to the waters being discharged into the wetlands. The existing wetland acts as a retention/detention basin that settles solids, absorbs nutrients through plant growth during the growing season, and provides a habitat for a variety of macro- organisms that live on aquatic vegetation that have the ability to use and transform various metals and other chemicals from toxic or animal damaging forms to useable forms. MITIGATING MEASURES (from the Mitigation Document for The Orchards Mixed Use Development, November 1991) 1. Because the proposed action must comply with the requirements of the King County Surface Water Design Manual (KCSWDM) and because the proposed action will have no off-site surface water impacts which are not addressed by the KCSWDM, mitigation of off-site adverse surface water impacts will be achieved through compliance with KCSWDM. 2. Because the proposed action must comply with the requirements of City of Renton Aquifer Protection Area Ordinance, adequate mitigation of potential groundwater impacts will be achieved through compliance with that ordinance, including the restriction on the storage or production of regulated compounds. Refer to the mitigation measures for wetlands for additional storm drainage mitigation measures. SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS During construction, temporary erosion and sedimentation could occur. Discharge from runoff would contain certain pollutants. 95054A-1.DOC;02/09/96; Page:17 WETLANDS A discussion of the existing plant communities and species of animals expected or observed on- site is found in the FAUNA and FLORA sections of the 1982 DEIS Northward Rezone and Development. These sections also assess the anticipated environmental impacts, mitigating measures, and significant unavoidable adverse impacts to the existing on-site plants and animals as a result of site development. This section of the Addendum focuses on the existing wetlands on-site and the resultant impact of project implementation on these wetlands. Although the 1982 DEIS did note areas of standing water on-site, that DEIS did not confirm that these areas met the criteria to be defined as wetlands. The proposed action in the 1982 DEIS included filling these areas. Since that time, additional wetland areas have been identified on-site and described in the June 1989 IES Associates report, using criteria established by the Corps of Engineers (COE). The COE's technical guidelines use vegetation, soils and hydrology for wetland identification and delineation. Generally, a minimum of one positive wetland indicator for each of the three parameters must be found in order to make a positive wetland determination. The IES report includes an assessment of these existing wetlands and a discussion of the proposed wetland enhancement plan. The report is included as Appendix E, to the June 1989 Expanded Environmental Checklist for the Renton East Residential Development. AFFECTED ENVIRONMENT On-Site Wetlands Sectors E/F and G include three delineated wetlands: #5, #6 and #7. They are described as follows: Wetland #5: 3,485 square feet, Class III; palustrine scrub/shrub. Vegetation consists of creeping buttercup, blackberry and Douglas' spirea. Functionally, this rather small wetland collects and discharges groundwater but does not perform any significant biofiltration purpose. The wetland and small surrounding area provide habitat for passerine birds and a variety of mammals, including mountain beaver, chipmunks and chickaree during the wet seasons. During this same time period coyote, raccoon, and skunk probably hunt the area for salamanders and Pacific tree frogs. Because of the small size of the wetland and the short duration of the period of standing water, the wildlife is not outstanding. Additionally, no endangered or threatened species were identified. Proposed Action: Fill the entire wetland. Wetland #6: 6,534 square feet: Class 11I; palustrine scrub/shrub. This wetland is primarily a drainage channel and vegetation consists of skunk cabbage, slough sedge, and Douglas' spirea. Functionally, it serves the same groundwater collection and discharge purposes as wetland #5. Because of its proximity to wetland #5, the wildlife habitat values are the same as those for wetland #5. Proposed Action: Fill the entire wetland. 95054A-1.DOC;02/09/96; Page:18 Wetland #7: 106,7022 square feet; Class II; palustrine forested and palustrine scrub/shrub. Stormwater enters this wetland from an 18" culvert running under Duvall Avenue N.E. and the exits the wetland through a 36" culvert running west under Duvall Avenue N.E. The main function of the wetland is detention during the wet seasons of the year. The northern two-thirds of the wetland is classified palustrine forested because of the dominance of an Oregon ash/alder overstory. Trees in the surrounding vicinity are red alder, western red cedar and Douglas fir. The southern one-third is categorized as a palustrine scrub/shrub because of the overstory of alder, black cottonwood and big-leaf maple combined with an understory primary of hardback. (Overall, the understory varies greatly throughout the wetland.) The southern portion of the wetland has been disturbed through tree removal and filling and is dominated by off-road vehicle tracks and refuse. Functionally, this wetland serves as a large detention pond for surface water runoff in the wet seasons of the year. It also provides habitat for birds and mammals typically found in urban areas. In the higher elevations on the edge and off the site to the north and east of the northern two- thirds of the wetland, evidence indicates the possible intermittent temporary use of the site by pileated woodpecker and large raptors. Animal species on the site include chickaree, chipmunks, and mountain beaver. Coyote, raccoon, and skunk probably hunt the amphibian populations in the area during the wet seasons. Proposed Action: Fill a small segment of the north end of the wetland for the extension of N.E. 6th Street; expand the wetland by excavating to create small open water component and terracing the side slopes; provide a buffer between the wetland and Duvall Avenue N.E. ENVIRONMENTAL IMPACTS The majority of the on-site vegetation (primarily second growth forest with fir and alder trees predominating) has been cleared for construction of the proposal. In general, this clearing would reduce vegetation species diversity and density of vegetation. Due to the habitat removal, certain bird and mammal species would likely be forced to find replacement habitat or perish as development proceeds. Human-tolerant species would replace those species that could not use the replacement habitat. On-Site Wetlands The proposal would result in development of residential buildings, parking areas, streets and associated facilities surrounding the wetland on-site. Construction activities related to the proposal could cause increases in erosion and sedimentation to the on-site wetland and downstream habitat. The introduction of human activity near the wetland could also reduce the stability of wetland habitat. A wetland mitigation plan has been prepared by Terra Associates for all of The Orchards development. The proposal includes increasing the total on-site wetland acreage. The total area of all wetlands to be filled would be less than 1.0 acres in size; therefore no Corp of Engineers permits would be required. As part of the site plan, a buffer greater than 25 feet in width is planned around the wetland areas. The planned swale and detention system would increase biofiltration of surface water and contribution to groundwater recharge on-site. Refer to the 95054addendum.doc; 02/26/96; Page:19 WATER section of this addendum for more information on the role of the wetlands in the planned ' storm drainage system. MITIGATING MEASURES (from the Mitigation Document for The Orchards Mixed Use Development, November 1991) 1. The applicant shall, in order to mitigate the water quality and habitat impacts associated with filling wetland #5, replace the filled wetland area with 3,485 square feet of new wetland or 4,356 square feet of restored or enhanced wetland, all on the site. 2. The applicant shall, in order to mitigate the water quality and habitat impacts associated with filling wetland 46, replace the filled wetland area with 6,534 square feet of new wetland or 8,168 square feet of restored or enhanced wetland, all on the site. 3. The applicant shall, in order to reduce adverse impacts on water quality, restore the disturbed southern portion of wetland #7 by removing the refuse and eliminating the disturbances to the land contours. Similarly, the applicant shall restore the Duvall Avenue edge of the wetland by removing the debris and improving the vegetative environment. 4. The applicant shall, in order to limit impacts on the existing water quality and wildlife habitat, provide a 50 foot average buffer around the defined edge of the wetland, with a minimum buffer width of 20 feet desired. Narrower buffers may be approved by the Planning Section of the Development Services Division next to Duvall Avenue N.E. and the extension of N.E. 6th Street if necessary to prevent the filling of wetland merely to create a buffer between the wetland and the streets. 5. The applicant shall, in order to reduce impacts on existing water quality, replace on the site the filled wetland area at a ratio of 1.25:1 of new wetland to filled wetland area or restore or enhance existing wetland areas on the site at a ratio of 1.5:1 of restored or enhanced wetland area to filled wetland area. 6. The applicant shall, in order to limit the potential disruption of the functional value of new biofiltration swales, locate these swales away from roads whenever feasible. 7. The applicant shall, in order to limit the potential disruption of the functional value of wetlands and swales located adjacent to high activity uses, provide fencing around wetlands and swales as required by the Planning Section of the Development Services Division. 8. The applicant shall, in order to reduce potential adverse impacts to wetlands and swales, provide educational signing concerning the purpose and function of the wetland or swale at appropriate locations. 9. The applicant shall, in order to ensure the survival of the wetlands, perform a 5 year monitoring program. The monitoring program shall be designed and conducted by a consultant approved by the City of Renton. The applicant shall pay the cost of designing and conducting the monitoring program, including the cost of the consultant. The program shall include the following elements: 95054addendum.doc;02/26/96; Page:20 a. An initial report completed by the consultant upon completion of the creation, restoration, or enhancement of the first wetland or wetland buffer. The initial report will identify problems in obtaining materials, differences in sizes of materials than were originally called for in the approved Wetland Mitigation Plan, differences in spacing materials than were originally called for in the approved Wetland Mitigation Plan, replacement materials if necessary, and any other conditions that varied from the approved Wetland Mitigation Plan. Major departures from the approved Plan must be approved in advance of planting by the Planning Section of the Development Services Division. b. Twice a year monitoring. Monitoring will be conducted by the consultant in the spring after green-up (approximately May 15th after the vegetation has started to grow but has not reached a height where it would preclude an evaluation of secondary growth at the base of the cattail and larger plant stock material); and in the fall after the growth has ended prior to the dormant season, approximately November 1 st to 15th. C. An annual report submitted by the consultant to the Planning Section of the Development Services Division by Decemberl5th of each year. The report will include identification of all plant species, either planted or invading, measurements of relative cover and abundance of each, plant vigor, and plant vitality. Photo documentation will also be provided. d. An evaluation. After the receipt of each monitoring report, the Wetland Mitigation Plan will be evaluated by the consultant and the Planning Section of the Development Services Division to determine if the Plan is functioning as designed. If it is not, modifications will be made to the Plan as agreed to by the applicant and the Planing Section of the Development Services Division. In assessing the success of the Plan, the performance standards will be applied. SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS Removal of vegetation over much of the site would reduce plant and animal species diversity and abundance. 95054addendum.doc; 02/26/96; Page:21 TRANSPORTATION The traffic information for this Addendum is based on the analysis conducted by The Transpo Group in June 1989 and a supplemental report, also by The Transpo Group, completed in October 1989 in response to revisions to the site plan. The June 1989 analysis is included in Appendix D to the June 1989 Expanded Environmental Checklist for the Renton East Residential Development. The Supplemental Report is included in the Appendix to the October, 1989, Residential Development Application for The Orchards. AFFECTED ENVIRONMENT Description of Streets and Roads Transportation: The revised site plan for Sectors E/F and G will generate an estimated 1034 daily trips and 104 afternoon peak hour trips. This is a reduction from the traffic study conducted for the 1991 DSEIS, which estimated that the Sectors E/F and G project would generate 1821 daily trips and 200 afternoon peak-hour trips. When these trips were added to the predicted traffic volumes at the six area intersections analyzed, all intersections would continue to operate to Level of Service (LOS) D or better. In fact, the project would adversely affect the predicted LOS at only one intersection: Duvall Avenue N.E. and Sunset Blvd. N.E., which would drop from LOS C to LOS D. Based on City standards, LOS D or better is considered acceptable, so the project would not cause traffic operations to fall below City standards at intersections in the area. Most of the project-generated traffic is projected to use either Duvall Avenue N.E., Bremerton Avenue N.E., or N.E. 4th Street. This usage pattern is a result of the proposed internal project street system, which consists of a series of residential streets leading into new neighborhood collector streets (N.E. 6th and Bremerton Avenue N.E.), which in turn link to Duvall Avenue N.E. and N.E. 4th Street. To comply with City codes, the applicant must construct all new residential streets and neighborhood collector streets to City standards, which will make them of adequate size to handle predicted volumes. Presently, N.E. 4th Street is a fully developed major arterial. The widening of Duvall Avenue N.E. from 4 to 5 lanes is in the City's Six Year Transportation Improvement Program. With respect to parking impacts, the project is providing a total of 438 on-site parking spaces, which exceeds the City's parking requirements. Consequently, the project would not cause any adverse impacts on the parking supply in the surrounding area. Truck traffic in the area will increase during the periods of construction activity. Truck traffic after completion of the project will be minimal, as it will consist only of delivery vehicles and occasional moving vans. Transit service is provided to the project area by Metro routes i I l and 147 on N.E. 4th Street. These routes provide service to downtown Renton, South Bellevue, and downtown Seattle. According to Metro, a proposed service change has been proposed for route 240 to serve Coal Creek Parkway, Duvall Avenue N.E., and N.E. 4th Street. This route would operate seven days a week and provide direct service to downtown Bellevue, and offer connections at the South Renton Park and Ride with Metro service to downtown Seattle and South King County destinations. This route would become the main transit service for the proposed project. 95054addendum.doc; 02/26/96; Page:22 To mitigate the increased demand placed on transportation facilities by the uses in the proposed project, a variety of transportation mitigation measures are being recommended. They can be grouped into the following categories: a) Physical improvements to mitigate the dependence on single occupancy vehicles by encouraging the use of the proposed new transit service on Duvall Avenue N.E. b) A Transportation Management Plan (TMP) designed to decrease the dependence of residents on single occupancy vehicles; c) Participation on a "fair share" basis in the NE 3rd/NE4th Street Traffic Benefit Zone; d) Support of the Duvall Avenue N.E. widening project to mitigate traffic impacts on the street; and Additionally, mitigation measures are proposed to lessen the impacts of construction traffic on adjacent streets and residential areas. MITIGATION MEASURES (from the Mitigation Document for The Orchards Mixed Use Development, November 1991) 1. The applicant shall, in order to reduce traffic impacts associated with the dependence on single occupancy vehicles, provide direct pedestrian access routes from internal residential streets to Duvall Avenue N.E. to encourage use of the proposed new transit service on Duvall Avenue N.E. Pedestrian routes to Duvall Avenue N.E. must have hard surfaces and adequate pedestrian-level lighting to provide safe use during low light hours. The pedestrian routes and lighting shall be approved by the Planning Section of the Development Services Division as part of the site plan process. 2. The applicant shall, in order to reduce traffic impacts associated with the dependence on single occupancy vehicles, also provide the concrete bases and necessary easements for one transit shelter on Duvall Avenue N.E to encourage increased use of transit. Location of the transit shelter base and easement shall be approved by Metro, the Planning Section of the Development Services Division, and the Transportation Services Division as part of the site plan process. 3. The applicant shall, in order to reduce project-generated traffic impacts, voluntarily contribute a traffic mitigation fee. The Traffic Mitigation Fee is to be established at the time of application for a Building Permit for any element of the proposed project based on the number of average weekday trips which are generated by the elements for which a Building Permit is being sought. The fee shall be paid at the time of issuance of a Building Permit. If the applicant cancels the Building Permit in writing, then the unencumbered portion of the fee plus accrued interest will be refunded to the applicant. 95054addendum.doc; 02/26/96; Page:23 4. The applicant shall, in order to reduce traffic impacts on internal project area streets, construct " N.E. 6th Street west of Duvall Ave. N.E. as a full width neighborhood collector street. The applicant shall receive a credit toward the Traffic Mitigation Fee for the value of any street right-of-way which exceeds that required by City ordinance(s). The applicant shall be reimbursed through a Latecomers Agreement for the value of any street improvement(s) which exceeds that required by City ordinance(s). 5. The applicant shall, in order to reduce traffic impacts on Duvall Avenue N.E. caused by construction vehicles, provide temporary traffic control measures on Duvall Avenue N.E. during periods of site preparation and construction. Temporary traffic control measures and any proposed hauling route(s) shall be approved by the Transportation Services Division prior to issuance of any site preparation/building permit. 6. The applicant shall, in order to reduce noise and safety impacts caused by the operation of construction vehicles on nearby residential streets, limit construction vehicle access to the site to Duvall Avenue N.E. 7. The applicant shall, in order to reduce traffic impacts caused at I-405 and N.E. 4th Street and at I-405 and Sunset by the operation of construction vehicles during peak hours, restrict hauling activities to the hours of 8:30AM and 3:30PM or submit a hauling route for approval which avoids these interchanges. 8. The applicant shall, in order to reduce the noise impacts on residential areas caused by construction vehicles, restrict construction activity to the hours of 7:OOAM to 8:OOPM, Monday through Saturday. No construction activity shall be permitted on New Years Day, Thanksgiving Day, the day before Christmas and Christmas Day. SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS. Additional vehicular trips would be generated by the proposal which would add to the existing peak hour traffic along Duvall Avenue N.E., 4th Street N.E., and Sunset Boulevard. 95054A-1.DOC;02/09/96; Page:24 PUBLIC SERVICES SCHOOLS This section addresses the impacts of the on-site population on Renton School District No. 403. Due to the changes in population trends and changes in the status of schools in the District since the publication of the 1982 DEIS, this section has been updated using 1995-1996 figures. AFFECTED ENVIRONMENT The project site is located within Renton School District No. 403. Students in the vicinity of the project attend Maplewood Heights Elementary School (K-6), Highlands Elementary School (K- 6), McKnight Middle School (grades 7 and 8) and Hazen High School (grades 9 through 12). ENROLLMENT OF SCHOOLS IN THE VICINITY OF THE PROJECT SITE Enrollment as of 10/95 Highlands Elementary 576 2727 N.E. 9th Maplewood Heights Elementary 541 13430 144th Avenue S.E. McKnight Middle School 850 2600 N.E. 12th Street Hazen High School 1046 1101 Hoquiam Avenue N.E. Source: Renton School District No. 403, 1996. They have no current statistics as to the capacity of the schools. ENVIRONMENTAL IMPACT The Renton School District does not currently have any student generation information to determine the total number of school aged children. It is anticipated that, due to the smaller lots and demographic trends, the number of students generated by the homes in Sectors E/F and G will be less than typical single family neighborhoods. MITIGATING MEASURES (from the 1991 Mitigation Document for The Orchards) 1. The applicant shall, in order to reduce the potential impacts of increased demands placed on the Renton School District by project residents, pay the City of Renton School Mitigation Fee, if any, in effect at the time of issuance of a Building Permit for each residential element of the project. If no fee is in effect at the time, the applicant may voluntarily pay an amount determined by applying the King County School Mitigation Fee for the next closest district to the project. 9505.1addendum.doc;02/26/96; Page:25 SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS None are expected. PARKS AND RECREATION Due to changes in the site plan and the proposed on-site recreational facilities, this section has been updated since publication of the 1991 DSEIS. AFFECTED ENVIRONMENT The 18 acre site is privately owned. There were two single-family homes on-site. The site may be used at times for unauthorized recreational activities (i.e., hiking, dog walking). Recreational opportunities in the vicinity of the site include several neighborhood and community parks within three miles of the site, including Cedar River Community Park, Liberty Community Park, Gene Coulon Memorial Beach Park, Kiwanis Park, Windsor Hills Neighborhood Park, Highlands Neighborhood Park and Community Center and the proposed Heather Downs neighborhood park. Maplewood Golf course is also a public recreation facility near the project site. ENVIRONMENTAL IMPACTS Implementation of the proposal would generate an on-site population of about 215 residents (based upon 2.0 persons per single-family unit and 1.5 per townhouse). This added population to the City would contribute to the demand for both private and public recreational facilities. (Note: This added population figure is less than the 360 residents anticipated for the previously approved plan for 212 apartments.) In order to help meet this demand, the site plan for Sectors E/F includes construction of a 1/2 acre neighborhood park for both active and passive recreation. In addition, approximately 43 percent of the townhouse area (Sector G) would be retained in landscaped/open space areas as wetland and wetland buffers. Landscaped pathways to these active and passive areas are planned to facilitate pedestrian access. These recreational opportunities are designed to serve the 122 homes and townhomes. The proposal does not include on-site recreational facilities for the 63 multifamily units (Sector D) to be located south of N.E. 6th Street, west of Bremerton Avenue. As a result, the population generated by this portion of the development would add to the area-wide demand for recreational facilities. 95054addendum.doc;02/26/96; Page:26 MITIGATING MEASURES (from the 1991 Mitigation Document for The Orchards) 1. The applicant may, in order to reduce the potential impacts on existing park and recreational facilities, incorporate a system of pedestrian and/or bicycle trails in wetland buffers, portions of wetland buffers, or along drainage swales, provided that the trails not infringe on the inner 20 feet of any buffer. Trails should meet the standards of the Parks Department. The location of trails shall be approved by the Planning Section of the Development Services Division and the Parks Department. 2. The applicant shall receive a credit toward any parks mitigation fees for the value of recreational trails and park facilities constructed. The eligible trails and facilities and the amount of the credit, if any, shall be determined by the Parks Department. 3. The applicant shall, in order to reduce the potential impacts on existing park and recreational facilities, deed an additional right of way, if any, necessary to accommodate a bicycle path on both sides of Duvall Avenue N.E. The applicant shall receive a credit toward any parks mitigation fees for the value of the bike path right(s) of way dedicated. The amount of the credit shall be determined by the Parks Department. 4. The applicant shall, in order to reduce the potential impacts on existing park and recreational facilities, pay a Parks Comprehensive Plan Mitigation Fee in effect at the time of issuance of a Building Permit for each element of the project. 95054addendum.doc; 02/26/96; Page:27 UTILITIES WATER SUPPLY AFFECTED ENVIRONMENT The project site is located within the City of Renton Water Service area. An existing 16-inch diameter water main is located in Duvall Avenue N.E. with an 8" line located in N.E. 6th Street. There are also water lines located within the Windsor Apartments complex. ENVIRONMENTAL IMPACTS Major improvements to the City of Renton's overall water system would not be required as part of the proposal. The proposal would generate a water demand of about 21,500 gallons per day, assuming a demand of about 100 gallons per person per day (this is less than the 36,000 gpd anticipated for the previously approved plan for 212 apartments.). According to City of Renton Public Works Department, the existing municipal water system would be sufficient to accommodate the proposal given construction of needed utility extensions. The water system plan to serve the site includes a connection with an existing 16-inch diameter water main located in Duvall Avenue N.E. and an 8" main in N.E. 6th Street. The water line would be extended to the site and branch to accommodate the development. Under this plan, fire flow at the site is estimated at 3000 gpm by the City of Renton Public Works Department. Improvements by the proponents include construction of new 8 inch looped water lines within each of the Sectors. MITIGATING MEASURES None are considered necessary. SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS None are expected. SEWER AFFECTED ENVIRONMENT With the construction of the Renton Highlands interceptor along the N.E. 4th Street corridor, sanitary sewer service is available to The Orchards and the past moratorium has expired. Sectors E/F and G will be served by the 12 inch mains constructed in Duvall Avenue N.E. with standard extensions within the sectors. The flows anticipated by the development of Sectors E/F and G have been calculated and incorporated into the city plans for the Renton Highlands interceptor. The total number of residents for this proposal is less than the number anticipated for the 1991 DSEIS, resulting in less impact on the sewer system. 95054addendum.doc;02/26/96; Page:28 MITIGATING MEASURES None are considered necessary. SIGNIFICANT UNAVOIDABLE ADVERSE IMPACTS None are expected. 95054addenduni.doc; 02/26/96; Page:29 DODDS ENGINEERS, INC. C I V I L F- N f I f,.i F L f-; I N G S LI R V E Y I N G P L A N N I N G LEVEL 2 STORM DRAINAGE ANALYSIS FOR THE ORCHARDS RENTON, WASHINGTON aHA N 4,wog � tr Date: April 15, 1996 w �+ Project No.: 95058 Prepared by: Robert H. Stevens 29715 Approved by: Gary R. Sharnbroich, P.E. °`�. 'GrsrE4`�� s`s, EXPIRES 12/28/ +-)(444 4205 1 48T1--1 AVE. N.E., SUITE 200 - BELLEVUE. WA 98007 (206) 885-7877 FAX: (206) 885-7963 LEVEL 2 STORM DRAINAGE ANALYSIS FOR THE ORCHARDS This report is an addendum to the original Storm Drainage Calculations for The Orchards written by Dodds Engineers, Inc., dated April 4, 1994. This Level 2 Analysis is in response to flooding problems encountered during the winter of 1995 - '96. The capacity of the intended downstream system will be analyzed in this report. In order to sufficiently analyze the system, the swale and existing 36-inch culvert were surveyed to determine lengths, invert elevations, and slopes. The discharge of the 36-inch outfall from detention system "300" is to a wide grassy swale. This swale is generally wide and nondescript; for the purposes of this report, it will be assumed to have a five foot bottom width and 5:1 sideslopes. This swale has two twelve-inch culverts within the channel. These culverts will be inundated during storm events and so are neglected in this analysis. The swale flows into a 36-inch pipe system which drains under Bremerton Avenue. This conveyance system flows through the adjacent apartment buildings and through the Safeway parking lot. The ultimate discharge for this conveyance system is on the south side of N.E. 4th Street. See Figure 1 to for pipe lengths and slopes. A backwater analysis was conducted on the downstream pipe system and swale. For the purpose of this report, tailwater elevations will be assumed contiguous with the outfall pipe crown on the south side of N.E. 4th Street. Two cases have been analyzed for this system showing the effect of the predeveloped flows and developed flows. The Routing Summary Table from the original Storm Drainage Calculations shows the 100-year peak flow rate for the predeveloped conditions to be 23.3 cfs, and 18.4 cfs for the developed 100-year peak. Both of the peak flow rates were analyzed by the pipe backwater method and the direct step backwater method for open channels. This analysis does not take into account the additional flow from the apartments or the Safeway parking area. It is merely a comparison of the existing conditions to the developed conditions. Basically, the calculated downstream effect of the developed drainage system is that it reduces the capacity for flooding in the channel and the pipe system. For the predeveloped flow condition, the backwater effect of the 23.3 cfs yields a headwater elevation at the 36-inch intake of 389.05. The backwater effect through the grassy swale ends up as the normal depth for the channel (symbolized by the negative value for So-Sf term before reaching the 772 feet channel length). The normal depth of the channel is 1.03 equating to a water elevation at the 36-inch outfall of 390.43. For the developed flow condition, the backwater effect of the 18.4 cfs yields a headwater elevation at the 36-inch intake of 388.98. The backwater effect through the grassy swale ends up as the normal depth for the channel (symbolized by the negative value for So-Sf term before reaching the 772 feet channel length). The normal depth of the channel is 0.919 equating to a water elevation at the 36-inch outfall of 390.32. These calculations confirm the reduction of the impacts caused by the storm drainage from The Orchards Development. Iry .. ....... - fo 01 '0 I eitc v�u No. 602 - f Ot i 4 10 it � 4 ' 2 � f I. E. ONSITE DETENTION CALCULATIONS 1. ROUTfNG SUMMARY A summary table of the resultant peak flows is attached below. . <€ RT ........... THE ORCHARDS DEI PROJECT NO. 88008 4-A r-94 WEST EAST BASIN BASIN EX. 1/2 2 YR PEAI{ FLOW RATE 1.7 cfs 2.2 cfs DEV. 2 YR PEAK RELEASE RATE 1.7 cfs 2.2 cfs EX. 2 YR PEAK FLOW RAPE 3.4 cfs 4.1 cfs DEV. 10 Y12 PEAK RELEASE RATE 3.4 cis 4.0 cfs EX. 100 YR, 24 I-1R PEAK FLOW RATE 16.1 cfs 23.3 cfs DEV. 100 YR, 24 I-IR PEAK RELEASE RATE 12.3 cfs 14.6 cfs EX. 100 YR, 7 DAY PEAK FLOW RATE 13.4 cfs 19.5 cfs DEV. 100 YR, 7 DAY PEAK RELEASE RAT 12.5 cfs 18.4 cfs 2 YR DETENTION VOLUME (cu-ft) 21,166 221,309 10 YR DETENTION VOLUME (cu-ft) 35,644 342,702 100 YR, 24 HR DETENTION VOLUME cu-ft 62,390 428,100 100 YR, 7 DAY DETENTION VOLUME (cu-f, 63,508 450,568 P ...... ...... . . %.%....-.....-.--.--...I...... .... ... ......... .........1............."...........l.l..... ............................ .. ...... . ........ .................... . .. . . .... . . . ................... . ........... . ....... . ......- . ... .... ... JOB NAME: ORCHARDS DONVNSTREAAI PREPARED BY: R.STEVENS JORNUMBER: 95058 DESICN STORM: 100 YEAR ENTRANCE ENTRANCE EXIT OUTLET INLET APPROACH BEND PIPE PIPE MAI 71GS OUTLET INLET PIPE FLOW VELOCITY TAILWATER FRICTION HGL READ HEAD CONTROL CONTROL VELOCITY HEAD HEAD HEADWATER SS ELEVATION FROM TO FLOW LENGTH DLIL ELEVATION ELEVATION AREA VELOCITY READ ELEVATION LOSS ELEVATION LOSS LOSS ELEVATION ELEVATION HEAD LOSS LOSS CB CB (CFS) (FEET) (IN) VALUE (FEET) (FEET) I(SQ M (FT/SEC) (FEET) (FEET) (FEET) (FEET) I (FEET) I(FEET)l (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) m 23.3 82 1 36 0.012 380.40 380.101 7.07 3.30 0.17 383.40 0.08 383.48 0.03 0.17 383.69 0.00 0.17 0.00 0.00 383.52 m K 23.3 72 36 0.012 380.10 390.50 7.07 3.30 0.17 393.52 0.07 393.59 0.03 0.17 393.90 0.00 0.17 0.22 0.00 383.95 K 1 23.3 120 36 0.012 390.50 380.80 7.07 3.30 0.17 393.85 0.12 383.97 0.03 0.17 394.17 0.00 0.17 0.22 0.00 384.22 i 1 23.3 271 36 0.012 390.90 381.70 7.07 3.30 0.17 394.22 0.28 394.70 0.03 0.17 394.90 0.00 0.17 0.17 0.00 394.90 1 H 23.3 29 36 0.012 381.70 392.13 7.07 3.30 0.17 394-90 0.03 385.13 0.03 0.17 385.33 0.00 0.17 0.17 0.00 385.33 H G 23.3 110 36 0.012 382.13 392.60 7.07 3.30 0.17 385.33 0.11 385.60 0.03 0.17 395.80 0.00 0.17 0.00 0.00 385.63 G F 23.3 25 36 0.024 392.60 382.86 7.07 3.30 0.17 385.63 0.10 385.96 0.03 0.17 396.06 0.00 0.17 0.00 0.00 385.99 F JE 23.3 40 36 0.024 1 382.86 393.001 7.07 3.30 0.17 385.89 0.17 386.06 0.03 0.17 396.26 0.00 0.17 0.00 0.00 386.09 E D 23.3 155 1 36 0.024 383.00 394.53 7.07 3.30 0.17 396.09 0.64 387.53 0.03 0.17 397.73 0.00 0.17 0.00 0.00 387.56' D C 23.3 50 36 0.024 384.53 394.86 7.07 3.30 0.17 397.56 0.21 387.96 0.03 0.17 389.06 0.00 0.17 0.00 0.00 387.89 c B 23.3 36 36 0.024 384.96 385.85 7.07 3.30 0.17 397.89 0.15 398.85 0.03 0.17 389.05 0.00 0.00 0.001 0.001 399.05 4/12/96 DODDS ENGINEERS,INC. PAGE 1 DIRECT STEP BACKWATER METHOD OPEN CHANNEL FLOW ORCHARDS DOWNSTREAM ANALYSIS DEI #95058 b= 5.00 Z= 5 Q = 23.30 n = 0.035 So= 0.0046 a= 1.75 Yn= 1.032 y A R R^(4/3) V aV^2/2g E dE Sf ave. Sf So - Sf ex X (1) 2.00 (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) 3.15 65.36 1.760662 2.126023 0.356474 0.003453 3.153453 3.31 E-05 3.00 60.00 1.685672 2.006153 0.388333 0.004098 3.004098 0.149355 4.17E-05 3.74E-05 0.004563 32.73465 32.73 2.501 43.75 1.434657 1.61807 0.532571 0.007707 2.507707 0.496391 9.72E-05 6.94E-05 0.004531 109.5643 142.30 2.001 30.00 1.181285 1.248742 0.776667 0.016392 2.016392 0.491316 0.000268 0.000182 0.004418 111.21931 253.52 1.50 18.75 0.923779 0.899686 1.242667 0.041963 1.541963 0.474429 0.000951 0.00061 0.00399 118.8919 372.41 1.00 10.00 0.65798 0.572291 2.33 0.147524 1.147524 0.394438 0.005258 0.003105 0.001495 263.8048 636.22 0.50 3.751 0.3713231 0.2668921 6.213333 1.049063 1.549063 -0.401541 0.0801781 0.042718 -0.03812 10.53401 646.75 :..........:........................... :.:;:;:o::.:� CiE�YiF.ERCa1I GGtATIOk15 ?i i:i:i:................... ....... :•:. .::,...:.:.:::....:...::.::.::..:.:::•:::::....:.:::.:.::::• JOB NAME: ORCHARDS DOWNSTREAM PREPARED BY: R.STEVENS , JOB NUMBER: 95058 DESIGN STORM: 100 YEAR ENTRANCE ENTRANCE EXIT OUTLET INLET APPROACH BEND JUNCTION PIPE PIPE MANNINGS OUTLET INLET PIPE FLOW VELOCITY TAILWATER FRICTION HGL HEAD HEAD CONTROL CONTROL VELOCITY HEAD HEAD HEADWATER FROM TO FLOW LENGTH DIA. n ELEVATION ELEVATION AREA VELOCITY HEAD ELEVATION LOSS ELEVATION LOSS LOSS ELEVATION ELEVATION HEAD LOSS LOSS ELEVATION CB CB (CFS) (FEET) (IN) VALUE (FEET) (FEET) (SQ FT) (FT/SEC) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) (FEET) M 18.4 82 36 0.012 390.40 380.10 7.07 2.60 0.11 393.40 0.05 383.45 0.02 0.11 383.59 0.00 0.11 0.00 0.00 383.47 M K 18.4 72 36 0.012 380.10 380.50 7.07 2.60 0.11 383.47 0.05 393.52 0.02 0.11 393.65 0.00 0.1 I 0.14 0.00 393.68 K 1 18.4 120 36 0.012 380.50 390.80 7.07 2.60 0.11 383.68 0.08 383.80 0.02 0.11 393.93 0.00 0.11 0.14 0.00 383.96 1 18.4 271 36 0.012 380.80 391.70 7.07 2.60 0.11 383.96 0.17 394.70 0.02 0.11 394.83 0.00 0.11 0.11 0.00 384.83 I H 18.4 29 36 0.012 381.70 392.13 7.07 2.60 0.11 394.83 0.02 385.13 0.02 0.11 395.26 0.00 0.11 0.11 0.00 385.26 H G 19.4 Ito 36 0.012 382.13 392.60 7.07 2.60 0.11 385.26 0.07 385.60 0.02 0.11 385.73 0.00 0.11 0.00 - 0.00 383.62 F 18.4 25 36 0.024 382.60 382.96 7.07 2.60 0.11 385.62 0.06 385.96 0.02 0.11 395.99 0.00 0.11 0.00 0.00 385.88 F E 1 18.41 40 36 0.024 382.86 383.00 7.07 2.60 0.11 385.98 0.10 396.00 0.02 0.11 396.13 0.00 0.11 0.00 0.00 396.02 E D 18.4 155 36 0.024 383.00 384.53 7.07 2.60 0.11 396.02 0.40 387.53 0.02 0.11 397.66 0.00 0.11 0.00 0.00 387.55 D C 18.4 50 36 0.024 394.53 384.96 7.07 2.60 0.11 397.55 0.13 387.96 0.02 0.11 387.99 0.00 0.11 0.00 0.00 387.88 B 18.4 36 36 0.024 384.86 395.85 7.07 2.60 0.11 387.88 0.09 398.85 0.02 0.11 388.98 0.00 0.00 0.00 0.00 M8.98 4/12/96 DODDS ENGINEERS,INC. PAGE 1 DIRECT STEP BACKWATER METHOD OPEN CHANNEL FLOW ORCHARDS DOWNSTREAM ANALYSIS DEI #95058 b= 5 Z= 5 Q = 18.4 n = 0.035 So= 0.0046 a= 1.75 Yn= 0.919 y A R R^(4/3) V aV^2/2g E dE Sf ave. Sf So - Sf AX X (1) (2) (3) (4) (5) (6) (7) (8) (9) (1 0) (11) (12) (1 3) 3.13 64.6345 1.75067 2.109951 0.284678 0.002202 3.132202 2.13E-05 3.00 60 1.685672 2.006153 0.306667 0.002556 3.002556 0.129647 2.6E-05 2.36E-05 0.004576 28.32963 28.33 2.50 43.75 1.434657 1.61807 0.420571 0.004807 2.504807 0.497749 6.06E-05 4.33E-05 0.004557 109.2343 137.56 2.00 30 1.181285 1.248742 0.613333 0.010222 2.010222 0.494584 0.000167 0.000114 0.004486 110.2454 247.81 1.50 18.75 0.923779 0.899686 0.981333 0.026169 1.526169 0.484053 0.000593 0.00038 0.00422 114.7086 362.52 1.00 10 0.65798 0.572291 1.84 0.092 1.092 0.434169 0.003279 0.001936 0.002664 162.9909 525.51 0.50 3.75 0.371323 0.2668921 4.906667 0.654222 1.154222 -0.06222 0.0500011 0.02664 -0.02204 2.823124 528.33 0 6 _ - NE,10TH ST H tl -1 c f J Drainage Bas i _ r ( t (245Acres) S1 I H �H o Drainage Basin /I (245Acres) 0 ti f Jl r NE;8TH STK o� Renton City Limits DO >K> G ° DWr <t rk 0 J ^ ° $ SY�0Oo�t cat, 0c A tj 06 Fi m ' O O U 00o c ° �r P z x D o 3 o p J ENE 6TH ST�1 J r ! p Cu:, r O ,tt� ° ° o p o po w, °6) o oo a 9 O O Ww o o ° ° ° rap z W A C�7j V^0 >' 0 ° Q OW Proposed Infiltration Facility ° zYJ 00 ° o '> c •.� , ` 0 (Option 1) 0 0> ool crD 6> O �p O Chevron O „O -' C= J•� uo O Co O O X, 0Proposed Trunkline -p q,,-° t�Jn o on 2AMcDoilald o H To p ap CJ (O )0 ' - -,C.P c' —o 0 g . (-P- do c)c o^ 00 O O O 000 OC �, �4i 14 O 00 p ❑ o o Greenwood Memorial Park C or, � X W 00 O n _ J °o o Q IQ Location of Flooding Oc�^ ° o 0 8 z0 and Erosion Problem ° u c p ri o H ��" m W _fr w Existing 18"and 24" 'w ,� •• Stormwater Overflow Pipes 0 0 O 0 > p 0 ° Q H 3 c King County °' p 0 z Parks and Re, c O a z C 00 0 60 ENE 2ND ST° O 00 O y r1 O O 301 Monroe Ave NE 00 00 00 (Upper Balch Pit) L.... ° 0 0 >( 36"Perforated ❑ 0 J m p Xi, e 01 CD . g :,y F Infiltration Perforated U 0 0 _ 4 U Infiltration Pipe x Kin Count .a Renton Transfer Center 0 O o O o yX: 0 o x, King County Y o 0 cu Department of Transportation p ° 7 H Proposed Trunkline <j yc (Option 2B) oc- -_`"ter# X- Y- :f King County City of Renton Community and Emergency Center - Public Works Maintenance Shops oe000 00 Legend ATTACHMENT A-VICINITY MAP Proposed Infiltration Facility(Option 1) Proposed Trunkline(Option 2A) clry of NProposed Trunkline(Option 2B) --'`Renton 0- 0 Drainage Basin Boundary Streams Parcels Feet 0 Existing Storm Structure 0 625 1,250 2,500 Existing Storm Pipe ;r ® � OOOOS ENGINEERS, INC. CIVIL ENGINEERING S U R V E Y I N G R L A N N I N G 2C5 STORM DRAINAGE CALCULATIONS FOR THE ORCHARDS Renton, Washington s T 1i i Prepared By: Gary R. Sharnbroich, P.E. Approved By: Edgar T. Jones, P.E. D.E.I. Project No. 88008 .Date: April 4 1994 EXPIRES 12 i 2d 1 4 .9 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE, WA 913007 [2061 BB5-7B77 OR 454-3743 FAX:12061 B85-7963 1 TABLE OF CONTENTS A. TECHNICAL INFORMATION REPORT B. PROJECT OVERVIEW C. ONSITE DRAINAGE FEATURES 1. Existing 2. Proposed D. CORE AND SPECIAL REQUIREMENTS 1. CR#1 - Discharge at the Natural Location 2. CR#2 - Off-site Analysis 3. CR#3 - Runoff Control 4. CR#4 - Conveyance System 5. CR#5 - Erosion / Sedimentation Control Plan 6. CR#6 - Maintenance and Operation 7. CR#7 - Bonds and Liability 8. SR#1 - Critical Drainage Areas 9. SR#2 - Existing Master Drainage Plan 10. SR#3 - Master Drainage Plan 11. SR#4 - Basin and Community Plans 12. SR#5 - Special Water Quality Controls 13. SR#6 - Coalescing Plate Oil/Water Separators 14. SR#7 - Closed Depressions 15. SR#8 - Use of Lakes,Wetlands or Closed Depressions for Peak Runoff Quantity Control 16. SR#9 - Delineation of the 100 Year Floodplain 17. SR#10 - Flood Protection Facilities for the Type 1 and 2 Streams 18. SR#11 - Geotechnical Analysis and Report 19. SR#12 - Soils Analysis and Report E. ONSITE DETENTION CALCULATIONS 1. Preliminary Routing Summary 2. Existing Site Hydrology a. West Basin b. East Basin 3. Existing Upstream Mite Hydrology a. West Basin b. East Basin 4. Developed Site Hydrology a. West Basin b. East Basin 5. Hydrology Analysis a. West Basin b. East Basin F. BIOFILTRATION DESIGN CALCULATION 1. Biofiltration Swale Summary 2. Biofiltration Swale Calculations G. WETPOND CONCEPTUAL DESIGN CALCULATIONS H. LEVEL 1 OFF-SITE ANALYSIS 1. West Basin 2. East Basin A. TECHNICAL INFORMATION REPORT THE ORCHARDS SITE PLAN APPROVAL Page 1 of 2 CONCEPTUAL DRAINAGE PLAN King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART I PROJECT OWNER AND PART 2 PROJECT LOCATION PROJECT ENGINEER DESCRIPTION ProjectOwner _Northward Properties Project Name The Orchards Address 1560 140th Ave NE Bellevue Location Phone (2 0 6) 7 4 7—17 2 6 Township 2-3 N Project Engineer Edgar T. Jones, P.E. Range 5E Section 10 Company Dodds Engineers, Inc. Project Size 62. 3 AC Address Phone 4205 148th Ave NE Bel 1 evue Upstream Drainage Basin Size 114 . 2 AC (206) 885-7877 PART 3 TYPE OF • OTHER Subdivision DOF/G HPA Shoreline Management Short Subdivision COE 404 Rockery 0 Grading DOE Dam Safety 0 Structural Vaults 0 Commercial FEMA Floodplain Other ® Other Site Plan n nrnva 1 [ COE Wetlands HPA Preliminary7Subdivision COMMUNITYPART5 SITE AND DRAINAGE Community Newcastle Drainage Basin T nwPr Q-cl i t R i wpr PART 6 SITE CHARACTERISTICS River 0 Floodplain Stream ® Wetlands Critical Stream Reach Seeps/Springs ® Depress io ns/Swales High Groundwater Table Lake 0 Groundwater Recharge 0 Steep Slopes Other Lakeside/Erosion Hazard PART 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities Alderwood 1 0 - 2 0 o mnc9 Pra tp Norm. Sandy Loam 1 0 - 6 o Slight Everett 2O Slight 0 Additional Sheets Attatched 1/90 Page 2 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATIONISITE CONSTRAINT © Ch.4-Downstream Analysis Reduce existing flow rate for selected design 0 storm - see report for specifics 0 0 a Additional Sheets Attatched PART 9 ESC REOUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION ® Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance [ Remove and Restore Temporary ESC Facilities © Perimeter Runoff Control Ey-:1 Clean and Remove All Silt and Debris Clearing and Grading Restrictions EZ Ensure Operation of Permanent Facilities ® Cover Practices Flag Limits of NGPES ® Construction Sequence Other Other PART 10 SURFACE WATER SYSTEM © Grass Lined Channel 0 Tank 0 Infiltration Method of Analysis © Pipe System C] Vault Depression SBUH Open Channel 0 Energy Dissapator 0 Flow Dispersal Compensation/Mitigation Dry Pond Wetland 0 Waiver of Eliminated Site Storage ® Wet Pond Stream Regional Detention Brief Description of System Operation Fx; sting nnsi:Le WPtlanc ,g-d fQL dot®ntien; pipe collection system to biofiltration swales prior to wetlands;op n FacilityRelated Site Limitations channels. 0 Additional Sheets Attatched Reference Facility limitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTS/TRACTS (May require special structural review) XD Drainage Easement Cast in Place Vault 0 Other ® Access Easement Retaining Wall ) Native Growth Protection Easement Rockery>4'High ] Tract 0 Structural on Steep Slope 0 Other PART 14 SIGNATURE OF - • • 1 or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and theAu '1r•C/ attatchments. To the best of my knowledge the information provided G�/ I here is accurate. ^•d��• 1/90 B. PROJECT OVERVIEW B. PROJECT OVERVIEW The proposed project area is approximately 62.3 acres located south of N.E. 8th Street, east of Union Avenue N.E. and west of Duvall Avenue N.E. within the City of Renton. The project site is currently undeveloped except for a small number of single-family residences. The project proposal is for development of the site in a combination of multi-family units, single-family residential lots, single-family townhomes and a small commercial complex. Public and private roadways, parking and recreation areas will be developed in support of the above units and lots. We have prepared these documents in accordance with the Orchards mitigation agreement, the King County Storm Drainage Manual, the predesign meeting on December 19, 1991, and subsequent design meetings and discussions with City of Renton staff. The main points are summarized below. 1. The west basin detention would be provided in Wetland #1 (to be enchanced). Offsite runoff will be directed to a wetland swale traversing the site before entering Wetland #1. Onsite flows shall be biolfiltered prior to entering the detention system. Biofiltration facilities may be located within the wetland buffered areas. Access roads shall be provided to all facilities for maintenance. 2. The majority of the east basin detention would be provided within Wetland #7 located in the southeast portion of the site. Detention shall be provided for the 2 year storm within Wetland #3 central to the site with provisions for overflowing the 100 year storm event. Wetland #4 central to the townhouse portion of the development would also be available for detention. Biofiltration and access shall be required as stated for the west basin. A. WEST BASIN The west onsite basin is 16.4 acres in size. There are five sub-basins within the west basin. Only the central basin has a well defined discharge point. The remaining sub-basins sheetflow across gravel access drives or into the rear yards of the neighboring properties. In order to not adversely affect the neighboring properties, we are proposing to combine the sub-basins and provide detention within wetland#1. The existing onsite swale will be relocated to align it with the proposed lot lines. It will discharge into the wetland enhancement / detention pond. Detention will be provided in order to release the developed onsite 24 hour - 2 year storm at 'h the existing 24 hour - 2 year storm runoff rate; the developed onsite 24 hour - 10 year storm at the existing 24 hour - 2 year storm runoff rate; the developed 24 hour - 100 year storm at the existing 24 hour - 100 year storm runoff rate; and the developed 7 day - 100 year storm at the existing 7 day - 100 year storm runoff rate. Since the standard peak rate runoff control performance is exceeded by the above criteria (i.e. existing runoff rates will be reduced) the safety factor of 30% need not be applied to the calculated detention volumes. Water quality facilities will be provided to treat onsite runoff prior to entering the detention facilities. Three separate biofiltration swales are proposed. One located at the northwest corner of the detention area, one located at the southeast corner of the detention area and one located along the east margin of Anacortes 200 feet south of NE 8th Street. The swales will be designed as wetland swales with a design water depth of 8 inches. 2. EAST BASIN The east onsite basin is 45.9 acres in size. The entire east basin combines to discharge to an existing 36 inch culvert at the south property line within Duvall Avenue NE. The north-central portion of the east basin has five depression areas within it. These areas are dry during the summer months, but contain water within the wetter winter months. All existing hydrograph generations assumed the conservative condition that the depression areas were dry as an initial condition. On and offsite hydrographs were routed through these depression areas for establishing the same discharge requirements as stated above for the west basin. A portion of the detention was provided within wetlands #3 and #4 with the major portion being provided within Wetland #7. Water quality facilities include a wetpond east of Wetland #3 with additional biofiltration swales dispersed throughout the site. C. ONSITE DRAINAGE FEATURES C. ONSITE DRAINAGE FEATURES 1. EXISTING CONDITIONS: The site is divided into an east and west drainage basin. The east basin is approximately 45.9 acres, all tributary to the 36" CMP discharge at the south end of the site on the west side of Duvall Avenue. The north portion of the basin contains a series of interconnected flat depressions which are dry during the summer months, but hold water during the wetter months. Some of the depressed areas have been classified as wetlands. Approximately 30.1 acres of offsite area to the northeast are tributary to this portion of the site. The runoff makes its way through the depressions, travelling generally to the southwest and then changing direction back to the southeast to a roadside ditch on the west side of Duvall Avenue, flowing to south. There is another large wetland in the southwest portion of the basin, east of Duvall Avenue. Offsite runoff from 13.2 acres flows through this wetland along with the onsite area, and is intercepted by a ditch along Duvall Avenue. This ditch also conveys runoff from another 24.4 acres of offsite area, as well as the runoff from the north portion of the onsite basin which crosses Duvall in an 18" culvert. At the south end of the site, the ditch is picked up by a 36" culvert crossing back across Duvall Avenue to the west. From this point the remainder of the east basin is also intercepted and the flows continue offsite to the south in a 36" CMP pipe. The west basin consists of approximately 16.9 acres of onsite area, with 46.5 acres of offsite area tributary to it. Runoff from the offsite area, as well as a small portion of the onsite area, flow into a small depression just south of N.E. 8th Street. It then continues to the southwest in a well defined flat channel that intercepts the majority of the remaining basin runoff. The channel itself has been classified as a wetland area. It flows offsite near the center of the basin and continues to the south, just to the west of the site. Runoff from the strip of area along the west property line sheet flows offsite across rear yards and is intercepted by the channel. Approximately 4.5 acres of the basin in the southwest corner of the site are tributary to a more defined discharge point in that corner, which also leads to rear yards of adjacent properties. 2. DEVELOPED CONDITIONS: The proposed development will continue to maintain the existing east and west drainage basins. Drainage from offsite basins will be collected in tight-line systems and conveyed either through the onsite detention/conveyance systems, or into the conveyance system in Duvall Avenue leading directly to the site discharge point. For the west basin, the development runoff from this onsite area will be collected via a network of catch basins and conveyance piping. Prior to discharging, the drainage will be directed to a 'T' type oil/water separator and then to one of a number of biofiltration swales. The existing channel that traversed the site will be replaced with a large grass-lined swale, conveying the offsite runoff through the site, prior to entering the detention/wetland facility and ultimately discharging to the existing offsite channel downstream. The onsite runoff will discharge from the biofiltration swales into the wetland enhancement area located in the western area of the single-family development. The wetland enhancement area will be bermed along the south side and affixed with a storm drainage control structure, to double as a storm water detention and treatment basin. The development in the east basin is to be comprised of commercial/office, townhomes, multi-family and single-family. The collection system will consist of the same type of features as described for the west basin. The existing broad swale traversing the basin will be replaced with a grass-lined swale in combination with three existing wetlands which will be enhanced. Flows from the 30.1 acres of offsite area currently entering the north portion of the site will be conveyed directly into the enhanced central wetland. Several onsite sub-basins will also discharge into this wetland after flowing through biofiltration swales or wetponds. A control discharge structure will allow a minimal depth of storm drainage detention in this wetland before the drainage enters the large grass-lined swale. The swale winds to the southeast through the proposed townhomes and into another smaller enhanced wetland within the townhome development. More of the onsite runoff will also be directed into this wetland, following treatment in biofiltration swales. This wetland will be used for detention as well, with a control structure discharging into another section of grass-lined swale flowing southeast to the intersection of Duvall Avenue and N.E. 6th Street. Biofiltration swales and conveyance pipes also converge to this point where a 24" culvert will cross Duvall to the east. The culvert leads to the large enhanced wetland in the southeast corner of the site. This wetland is to be used as the main detention facility with berms placed along the north, west and south sides. The 24.4 acres of offsite area which currently contribute runoff to the roadside ditch in this area, will be intercepted to the north in the conveyance system in Duvall and will bypass the detention pond. The control structure from this enhanced wetland will discharge to the existing 36" culvert crossing back under Duvall to the west. The bypass system also is directed to this pipe. The total combined flow then continues to the south off of the site. Joins sheet 5) Amc ISSAQUAH 12 MI. 10, 1 680000 FEET 1122007'C 47 A8D « •� 1 AmC ;gig"hIan• ti 6c, ; C• ^dry »~•• �I;,�I�; �i I .. - ' AgB- J ' _- .�z - An ' ( •� Trailer ��: n.EvB •, • lil1� ��■ ■• •� ark.•' i = ii' .B i 3 424 I Sh6 d e Greenwood Ce •II�� EvD i i-� •.�J I , , 180 1 �. • .� I : FEE ABC I �• •406 I .. •f1t Oli EvC Cenii'`y °\ `n An n n GRAVEL •PIT M �a nAgC ;P321 \a�w 1n ..••. --_ -= 1 14 -_ a AkF EvC IAkF i / •_ '+ i I �• � as �y�, ...• �'• ./q j ;•; «... L--�— -- -`I .' / "J/ • • •j y ice" i Ur Py ''` ♦ I ✓ AkF %�'~• ( . n i . I , I lBM 'n" i - I �`�,•_ ,I, .. --�/ .3 -;.r p a- EvB --AgC BM 37 AkF RIVER .Py d Golf x I o - `.Ceo 1•-- - ;- - it BC_ / •AkF J ?Y} I Ma r G I " QG•'a , 1 , � AkF s F \�� AgD ~!/ •P ). •�' ; PY _AkF_ \` ap• i�• p�I A hNg I �� 41N8 W mac_ 455 9�a�•8i/i ���(- [ '� •I ==I ___ \a cii =Ji •u •��'llOt PY� h ;n ai a �O a AgC \tom AkF Ur t \\ " I AkF Park Ng • % �°t, • AgC Py O AQ i,b'o AgC �C`d 'yo EvC AgD AkF r`Tj me 76 ------ - - -_1 --- ----e --- Q- •---- - - - -1 - _- -o BMt7----• BM 27' gC A B I _ Z _496 e • 1 , �. -AgCa "r AgC Agp - I AkF AmC i AgB t1 emg i Ag8 ` PIPELINE 'C qgg Ur : 27 4921 r 2 t G Sk I tia F AgC x I'Sk yo♦�♦�,� I per' A4 A�71RlJ'�ITBKJC, Elm ! ¢� i A ' B 470 -'--• -- =ua-• ---- -- t1 --- x— — -- -d — -- ------- -- 463 a � Itl c AgC AgB I GUIDE TO MAPPING UNITS For a full description of a mapping unit, read both the description of the mapping unit and that of the soil series to which the mapping unit belongs. See table 6, page 70, for descriptions of woodland groups. Other information is given in tables as follows: Acreage and extent, table 1, page 9. Town and country planning, table 4, page 57. Engineering uses of the soils, tables 2 and 3, Recreational uses, table 5, page 64. pages 36 through 55. Estimated yields, table 7, page 79. Woodland Described Capability unit group Map on symbol Mapping unit page Symbol Page Symbol AgB Aide r ood gravelly sandy loam, 0 to 6 percent slopes---------- 10 IVe-2 76 3d2 AgC Alder ood gravelly sandy loam, 6 to 1S percent slopes--------- 8 IVe-2 76 3dl AgD Alder ood gravelly sandy loam, 15 to 30 percent slopes-------- 10 VIe-2 78 3dl AkF Alde r ood and Kitsap soils, very steep------------------------ 10 VIIe-1 78 2d1 AmB Arents, Alder ood material, 0 to 6 percent slopes 1/---------- 10 IVe-2 76 3d2 AmC Arents, Alde r ood material, 6 to 15 percent slopes 1/--------- 10 IVe-2 76 3d2 An Arents, Everett material l/----------------------------------- 11 IVs-1 77 3f3 BeC Beausite gravelly sandy loam, 6 to 15 percent slopes---------- 11 IVe-2 76 3d2 BeD Beausite gravelly sandy loam, 15 to 30 percent slopes--------- 12 VIe-2 78 3dl BeF Beausite gravelly sandy loam, 40 to 75 percent slopes--------- 12 VIIe-1 78 3dl Bh Bellingham silt loam------------------------------------------ 12 IIIw-2 76 3w2 Br Briscot silt loam--------------------------------------------- 13 IIw-2 75 3wl Bu Buckley silt loam--------------------------------------------- 13 IIIw-2 76 4wl Cb Coastal beaches----------------------------------------------- 14 VIIIw-1 78 --- Ea Earlmont silt loam-------------------------------------------- 14 IIw-2 75 3w2 Ed Edgewick fine sandy loam-------------------------------------- 15 IIIw-1 75 2ol EvB Everett gravelly sandy loam, 0 to 5 percent slopes------------ 15 IVs-1 77 3f3 EvC Everett gravelly sandy loam, 5 to 15 percent slopes----------- 16 VIs-1 78 3f3 EvD Everett gravelly sandy loam, 15 to 30 percent slopes---------- 16 Vle-1 77 3f2 EwC 'Everett-Alde r ood gravelly sandy loams, 6 to 15 percent slopes------------------------------------------------------ 16 VIs-1 78 3f3 InA Indianola loamy fine sand, 0 to 4 percent slopes-------------- 17 IVs-2 77 4s3 InC Indianola loamy fine sand, 4 to 15 percent slopes------------- 16 IVs-2 77 4s3 InD Indianola loamy fine sand, 15 to 30 percent slopes------------ 17 VIe-1 76 4s2 KpB Kitsap silt loam, 2 to 8 percent slopes----------------------- 17 IIIe-1 75 2d2 KpC Kitsap silt loam, 8 to 15 percent slopes---------------------- 18 IVe-1 76 �d2 KpD Kitsap silt loam, 15 to 30 percent slopes--------------------- 18 VIe-2 78 2dl KsC Klaus gravelly loamy sand, 6 to 15 percent slopes------------- 18 VIs-1 78 3fl Ma Mixed alluvial land------------------------------------------- 18 VIw-2 78 2ol NeC Neilton very gravelly loamy sand, 2 to 1S percent slopes------ 19 VIs-1 78 3f3 Ng Newberg silt loam--------------------------------------------- 19 IIw-1 74 2o1 Nk Nooksack silt loam-------------------------------------------- 20 IIw-1 74 2ol No Norma sandy loam---------------------------------------------- 20 IIIw-3 76 3w2 Or Orcas peat---------------------------------------------------- 21 VIIIw-1 78 --- Os Oridia silt loam---------------------------------------------- 21 IIw-2 75 3w1 OvC Ovall gravelly loam, 0 to 15 percent slopes------------------- 22 IVe-2 76 3dl OvD Ovall gravelly loam, 15 to 25 percent slopes------------------ 23 VIe-2 78 3dl OvF Ovall gravelly loam, 40 to 75 percent slopes------------------ 23 VIIe-1 78 3dl Pc Pilchuck loamy fine sand-------------------------------------- 23 VIw-1 78 2sl Pk Pilchuck fine sandy loam-------------------------------------- 23 IVw-1 76 2sl Pu Puget silty clay loam----------------------------------------- 24 IIIw-2 76 3w2 Py Puyallup fine sandy loam-------------------------------------- 24 IIw-1 74 2o1 RaC Ragnar fine sandy loam, 6 to 15 percent slopes---------------- 25 IVe-3 77 4sl RaD Ragnar fine sandy loam, 15 to 25 percent slopes--------------- 26 VIe-2 78 4sl RdC Ragnar-Indianola association, sloping: l/---------------------- 26 -------- -- Ragnar soil---------------------------------------------- IVe-3 77 4sl Indianola soil------------------------------------------- -- IVs-2 77 4s3 RdE Ragnar-Indianola association, moderately steep: 1/------------ 26 -------- -- Ragnar soil--------------------------------------------- -- VIe-2 78 4sl Indianola soil------------------------------------------- -- VIe-1 77 4s2 U. S. GOVERNMENT PRINTING OFFICE:1973 0-468-288 D. CORE AND SPECIAL REQUIREMENTS D. CORE AND SPECIAL REQUIREMENTS 1. CORE REQUIREMENT#1: DISCHARGE AT THE NATURAL LOCATION (Refer to existing onsite drainage map in Existing Site Hydrology Section of this report). The entire east basin existing drainage is directed to a 36 inch culvert located at the southernmost property boundary and Duvall Avenue N.E. This discharge will be maintained. The west basin is divided into 4 subbasins. The west portion of Sector A (5 acre parcel fronting on Union Avenue N.E.) discharges to a small swale drainage southeasterly across the south Sector A property line. The remainder of Sector A and portion of the west basin north of Sector A's south property line is directed to a major swale crossing the south property line of Sector A. The remainder of the west basin sheet flows across the west boundary or is directed to a swale at the southwestern corner of the property. This drainage flows into existing driveways and yards of adjacent properties. Since the two swales crossing the Sector A meet up immediately offsite and the sheet flow across the west boundary is causing drainage problems, these flows were combined and discharged at the major swale crossing the south property line of Sector A. 2. CORE REQUIREMENT#2: OFFSITE ANALYSIS This core requirement is addressed in detail in Section H. Level 1 Off-Site Analysis contained in this report. 3. CORE REQUIREMENT#3: RUNOFF CONTROL Peak rate runoff control is provided through the use of detention. Existing site hydrology, Developed Site hydrology and the Hydrologic Analysis sections of this report detail the onsite detention calculations. A portion of the east basin offsite upstream flows are bypassed (the Forrest Crest basin and adjacent northern subbasin). The remaining offsite basins produce a flow less than 50% of the onsite developed flow for a 100 year 24 hour duration storm event. See Existing Site Hydrology portion of this report for details. 4. CORE REQUIREMENT#4: CONVEYANCE SYSTEM Conveyance systems are shown schematically on the preliminary grading and utility plans. The conveyance systems for the site will be sized in accordance with the storm drainage manual requirements during the design phase of the project. 5. CORE REQUIREMENT#5: EROSION/SEDIMENTATION CONTROL PLAN Erosion / sedimentation control facilities will be provided during the design / working drawings phase of the project in accordance with the requirements of the storm drainage manual. 6. CORE REQUIREMENT#6: MAINTENANCE AND OPERATION A homeowners association will be provided for the entire Orchards complex. Drainage facilities located outside of public right-of-way will be noted and maintained by this homeowners association. 7. CORE REQUIREMENT#7: BONDS AND LIABILITY Bonds and liability requirements will be met in accordance with City of Renton requirements. 8. SPECIAL REQUIREMENT#1: CRITICAL DRAINAGE AREA The project is located within the Maplewood Creek drainage basin. The lower reaches of this creek have experienced erosion control problems. In order to mitigate the Orchards impacts to these erosion control problems, the release rate for the 2 year design storm shall be 50% of the existing 2 year peak runoff rate and the release rate for the 10 year design storm shall be the existing 2 year peak runoff rate. Refer to the Hydrologic Analysis of this report for details. 9. SPEC1ALREQ #2-. COMPIIANCEWIIHANEXNMCMASIIRDRAINAGEPIAN This special requirement does not apply to the Orchards project. 10. SPECIAL REQUIREMENT#3: CONDITIONS REQUIRING A MASTER DRAINAGE PLAN Since the project is not a Master Planned Development, does not encompass a contiguous drainage subbasin of more than 200 acres, will not construct more than 50 acres of impervious surface or clear an area of more than 500 acres, a Master Drainage Plan will not be required. 11. SPECIAL REQUIREMENT#4: ADOPTED BASIN OR COMMUNITY PLANS This special requirement does not apply to the Orchards project. 12. SPECIAL REQUIREMENT#5: SPECIAL WATER QUALITY CONTROLS The site will have several discharges into the existing onsite wetlands. Those less than 1 acre of impervious surface subject to vehicular use will discharge via a water quality swale, those greater than 1 acre will discharge via a wetpond. Refer to Biofiltration Design Calculations and Wetpond Conceptual Design Calculations sections of this report. 13. SPECIAL REQUIREMENT#6: COALESCING PLATE OIL/WATER SEPARATORS The Orchards site will not be constructing more than 5 acres of impervious surface directed to any one discharge from the project site and thus does not require a coalescing plate oil /water separator. 14. SPECIAL REQUIREMENT#7: CLOSED DEPRESSIONS The Orchards project contains depression areas that have greater than 5000 square feet at overflow. Onsite dead storage will be maintained and onsite depression areas will be analyzed using the 100 year 24 hour duration and 7 day duration design storms. Refer to Onsite Detention Calculations section of this report. 15. SPECIAL REQUIREMENT#8: USE OF LAKES,WETLANDS OR CLOSED DEPRESSION FOR PEAK RATE RUNOFF CONTROL The Orchards project will use onsite depression and wetland areas for peak rate runoff control in accordance with the mitigation document for the project. Water quality controls will be provided in accordance with Special Requirement #5. Since the wetlands are contained onsite the floodplain of the wetlands will be increased more than 0.1 feet. Refer to the Onsite Detention Calculations section of this report for specifics. 16. SPECIAL REQUIREMENT#9: DELINEATION OF THE 100 YEAR FLOODPLAIN Since the Orchards contains wetlands, 100 year floodplains will be designated for the design working drawing phase of the project. 17. SPECIAL REQUIREMENT#10: FLOOD PROTECTION FACILITIES FOR THE TYPE 1 AND 2 STREAMS This section does not apply to the Orchards project since it neither contains or abuts a type 1 or 2 stream. 18. SPECIAL REQUIREMENT#11: GEOTECHNICAL ANALYSIS AND REPORT This section does not apply to the Orchards project. 19. SPECIAL REQUIREMENT#12: SOILS ANALYSIS AND REPORT The soils for this project have been mapped by the King County Soils survey and a Geotechnical report was prepared for a majority of the site. E. ONSITE DETENTION CALCULATIONS E. ONSITE DETENTION CALCULATIONS 1. ROUTING SUMMARY A summary table of the resultant peak flows is attached below. UW t U XXXX THE ORCHARDS DEI PROJECT NO. 88008 4-A r-94 WEST EAST BASIN BASIN EX. 1/2 2 YR PEAK FLOW RATE 1.7 cfs 2.2 cfs DEV. 2 YR PEAK RELEASE RATE 1.7 cfs 2.2 cfs EX. 2 YR PEAK FLOW RATE 3.4 cfs 4.1 cfs DEV. 10 YR PEAK RELEASE RATE 3.4 cfs 4.0 cfs EX. 100 YR, 24 HR PEAK FLOW RATE 16.1 cfs 23.3 cfs DEV. 100 YR, 24 HR PEAK RELEASE RATE 12.3 cfs 14.6 cfs EX. 100 YR, 7 DAY PEAK FLOW RATE 13.4 cfs 19.5 cfs DEV. 100 YR, 7 DAY PEAK RELEASE RATI 12.5 cfs 18.4 cfs 2 YR DETENTION VOLUME cu-ft 21,166 221,309 10 YR DETENTION VOLUME cu-ft 35,644 342,702 100 YR, 24 HR DETENTION VOLUME cu-ft 62,390 428,100 100 YR, 7 DAY DETENTION VOLUME (cu-f. 63,508 450,568 2. EXISTING SITE HYDROLOGY As previously discussed, the site's surface runoff is directed to either of two main drainage basins. Onsite features include a number of wetlands, flat depressed areas and broad swales. The soils onsite are mainly "Alderwood" with a hydrologic group classification of "C". There is an area of "Everett" type soils in the southwest portion of the site (hydrologic group "A"), and a small area of "Normal Sandy Loam" to the north (hydrologic group "D"). a. WEST BASIN: "Al": 10.7 acres, tributary to discharge point grasses/brush/forest @ CN = 83, no impervious area Time of Concentration (calculated by the Waterworks program) 120', sheet flow - brush/trees, slope = 3.6% 350', shallow flow - brush/trees, slope = 0.6% 50', grassed channel - slope = 4% 360', shallow flow through wetland, slope = 0.5% Tc = 49.6 minutes "A2": 1.2 acres, tributary to north depression (#10) similar to Al, CN = 83, no impervious area Time of Concentration: 130', sheet flow - dense grass, slope = 1.4% 100', shallow flow - grass, slope = 2% Tc = 27.0 minutes "J": 4.5 acres, tributary to SW corner of site brush/trees @ CN = 81, no impervious area Time of Concentration: 170', sheet flow - brush/trees, slope = 3.5% 150', shallow flow- grass/brush, slope = 1.5% 350', defined forest channel, slope = 1% Tc = 40.3 minutes b. EAST BASIN: "B": 0.9 acres, tributary to depression #31 brush/trees @ CN = 81, no impervious area Time of Concentration: 50', sheet flow - brush/trees, slope = 1% 90', shallow flow- brush/trees, slope = 11% Tc = 21.5 minutes "C": 3.1 acres, tributary to depression #30 brush/trees @ CN = 81, no impervious area Time of Concentration: 100', sheet flow - brush/trees, slope = 9% 120', shallow flow- brush/trees, slope = 3% 200', shallow flow- brush/trees, slope = 1.2% Tc = 23.3 minutes "D": 3.2 acres, tributary to depression #20 brush/trees @ CN = 81, no impervious area Time of Concentration: 190', sheet flow - brush/trees, slope = 1.5% 440', shallow flow - brush/trees, slope = 1% Tc = 61.9 minutes "E": 2.5 acres, tributary to depression #50 brush/trees @ CN = 81, no impervious area Time of Concentration: 70', sheet flow - brush/trees, slope = 12% 100', sheet flow- brush/trees, slope = 2% 100', shallow flow- brush/trees, slope = 2% Tc = 39.5 minutes "F": 10.8 acres, tributary to depression #40 brush/trees/grass @ CN = 81.5, no impervious area Time of Concentration: 175', sheet flow- brush/trees, slope = 1% 200', shallow flow- brush/trees, slope = 2.3% Tc = 60.5 minutes "G": 8.55 acres, tributary to Duvall Ave. culvert crossing brush/trees @ CN = 81, no impervious area Time of Concentration: 120', sheet flow - brush/trees, slope = 5% 180', sheet flow - brush/trees, slope = 1% 40', shallow flow- brush/trees, slope = 10% 650', defined forest channel, slope = 1.2% Tc = 89.5 minutes "H": 7.7 acres, tributary to discharge point 7.6 ac, brush/trees/grass @ CN = 83 0.1 ac, roofs, roads @ CN = 98 Time of Concentration: 150', sheet flow- brush/trees, slope = 2.5% 60', shallow flow- brush/trees, slope = 13% 160', shallow flow- brush/trees, slope = 3.7% 290', shallow flow- brush/grass, slope = 1% 310', grass/brush channel, slope = 0.5% Tc = 47.4 minutes "I": 9.17 acres, tributary to SW wetland 4.6 ac, brush/grass/trees (hyd. group "A") @ CN = 60 4.57 ac, brush/trees (hyd. group "C") @ CN = 81 Pervious CN = 70.5, no impervious area Time of Concentration: 260', sheet flow - brush/trees, slope = 9% 230', shallow flow - brush/trees, slope = 2.2 330', shallow flow- brush/trees/grass, slope = 0.6% Tc = 51.3 minutes Stage-storage and stage-discharge curves as well as topographic maps for the existing onsite depressions are included in this section. An overall drainage map is also attached. -1-� .�f� Y _�I�_:ST_�.�tli`r===___-:�- ►: 1�' ( I� t+` t l ` ti, ( _=____= 1 �� V -J • . '. �' t'I ',•w'l,+' ':!" r.l l' �, i •�' II VOL '' 'i'' •' �+`., t- so '.rY{--� ,' r1 r .•.-. ;f i .i 11 r. r t 1j �, n. trr rlr'�r'1t. ' fi to —rj1--�t1 C -- --_;� — TI1L! _ Irrr- -•:`T-.�j. Il ►' n .� 1 u1 ti (� a rzy , N p I tt r I �( .10L n U t1 C c O I I —,, , , `• •t, I �p -t�rr:"z^_- t ■.rf ' .• • I I �� (� �U A• !, ,,i � I •f'�._�` � Cl Ir .-r 14ty _--. _ ' .• r,a 'i ?,� "a it ,• I� • �• II . i 1� gib,;°, .• ;.;; � ---�•� :I'••• -•.n l.•' r 13— I III ' .� - o ) � '�;� �•J� _,1 I 'I I llpKttotr•11.1%(- rtl►ool;'�7, :'(: ,• I f : ' ' ..r. .•,�/� I 1 �� I . •�. .11, I'110,1•►I' '••', •.S;r' 1 r .,- i' „ •I,r { I t1 r �' 'I / tnl 01 .n . toilco ZI JIJI_LSl_-- t or L r I SIT J IcD r� _ - ,(off �• :.. -" �,' .• •,.•, '!�; � j�11 �//;1 'tij �� • ' r � I /I ^ .••�'�,' 1',y � t s't1 Y ',. .w.a �` 3a�L �- set_ rn .0 Its 43 or ID Sit I ^� _�_ �',•�; .�`' •I' I t :1 j:lj', '1'I�:i �' ''!; '.1! N ,ro U==1 f- 411. I' j ,►.• <,!w . tt�.-,: ?m -'s' to l .mot,—�• _ ... _1( '....r �,�. _ � —I, ,i;• � � .�I,'D J%!©.'Ir ,ii �•,, ('U' � or -.--ll II 1` D ��F r .,� �; Z;;i YI.�:r.�S.fl'I'•.i Is 1 I ` • • rA; *rn 1• .. 1 !i' �- it ,�, ,.�,• „ .,r.,'„ ;i • .. • — _4 R)r, II. i" ,. •" G, , ' (��•, .,•:p' ►• \ _ __fit IN 00 D O - I !n� I �o. ItLrJ?. )IJ 1 U• n , I ]�► -- -- _ t���= .tJ 1 ! °'' ► � I -►rt7buAu'IL t �- =�:.•ti r:o•j.'}•'ra. •1: .,t!r'i).:•,.I•.` hr�l''•� •-.1::1' — �' It 1 t 1 �I ,• .r .: '•,ri,.lr••: ":...i..r :.t.,�:.:• •t•r,, "ti`cu '',,{1•I�:'r'•'�••,;. •,�,' t' '1• ;�,�'''(i':;:.a• /:�')•' O't>�;,'!;,''• ,rii'!.?.:,:,:•1' hl.l,os t.. �.r.�� i !.t'-'l :`` ',t+.l I•.`:, 1'rl.� .,,1�,,'Ir t''r„^.,111•j•..•4�(:It r.j, 1r r, 1' � .► i/'irM..1• II•• .1 ,,LM r r;)rr ((.r ,.I ,!. S •t ••f:.• '�I,1:)r 1/ •J"!/•,•. ♦ ,1, ." �!1• ,,a11: .Ir�d'�.Ir'•1;11:'I;'l til' �,'','l i.:ia,�': , tllo�:',I• rya _ ■� �• 'i •Ad/rillilJrrfbvlNo!�If�f1—t 'J• (' . of urban Pisanln p/ uff, 'rq. I:1tN' •e ' r'�' k.It1I, r.,.',L�J ' 'Y�•�' 1.1 ►Mahlon, o/S/clbn ' A'•, " w) 7 i,Wo/atf•P•lt..•'+� <ii'l.;!r• 1-:-.�6rw.J-Ilrw \I I `'t/� ' 1 • �albh u,r r ) • V I p tJLal/d Ilr�rb�il Iro(aNlort V►u.. 11d.Aj 16r,0 .. .—:° -•�---• r7 ' ------------------------------------- --- ---- --- -- --- z - � • ,10r I F IL I 1 c '`A zpvo 1 %k 40 i ' •� j I G i I � I o o i ► \ EXISTING ONSITE ! CONDITIONS I 1/23/92 Dodds Engineers , Incorporated page 1 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS EX DEPRESSIONS STAGE STORAGE TABLE CUSTOM STORAGE ID No. 10 Description: EX WEST STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- 398.00 0.0000 0.0000 398.70 695.00 0.0160 399.40 4935 0.1133 400.10 14784 0.3394 398.10 23.000 0.0005 398.80 985.00 0.0226 399.50 5778 0.1326 400.20 17338 0.3980 398.20 46.000 0.0011 398.90 1275 0.0293 399.60 7068 0.1623 400.30 19892 0.4567 398.30 69.000 0.0016 399.00 1565 0.0359 399.70 8359 0.1919 400.40 22446 0.5153 398.40 92.000 0.0021 399.10 2408 0.0553 399.80 9649 0.2215 400.50 25000 0.5739 398.50 115.00 0.0026 399.20 3250 0.0746 399.90 10940 0.2511 398.60 405.00 0.0093 399.30 4093 0.0940 400.00 12230 0.2808 1/23/92 Dodds Engineers , Incorporated page 2 DRAINAGE ANALYSIS THE ORCHARDS -- 88008 EX DEPRESSIONS --------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 20 Description: EX. DEPRESSION EAST STAGE (----STORAGE----> STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----> Ift) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- ________________ 394.50 0.0000 0.0000 395.30 431.50 0.0099 396.10 1789 0.0411 396.90 5897 0.1354 394.60 14.000 0.0003 395.40 552.00 0.0127 396.20 2302 0.0528 397.00 6410 0.1472 394.70 28.000 0.0006 395.50 672.50 0.0154 396.30 2816 0.0646 391.10 7855 0.1803 394.80 42.000 0.0010 395.60 793.00 0.0182 396.40 3329 0.0764 397.20 9300 0.2135 394.90 56.000 0.0013 395.70 913.50 0.0210 396.50 3843 0.0882 397.30 10746 0.2467 395.00 70.000 0.0016 395.80 1034 0.0237 396.60 4356 0.1000 397.40 12191 0.2799 395.10 190.50 0.0044 395.90 1155 0.0265 396.70 4870 0.1118 397.50 13636 0.3130 395.20 311.00 0.0071 396.00 1275 0.0293 396.80 5383 0.1236 1/23/92 Dodds Engineers , Incorporated page 3 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS EX DEPRESSIONS --------------------------------------------------------------------- --------------------------------------------------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 30 Description: EX. DEPRESSION EAST STAGE (----STORAGE----) STAGE c----STORAGE----> STAGE (----STORAGE----) STAGE (----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- -------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------- 398.80 0.0000 0.0000 399.30 1218 0.0280 399.90 3061 0.0703 400.50 8730 0.2004 398.80 0.0000 0.0000 399.40 1461 0.0335 400.00 3400 0.0781 400.60 10860 0.2493 398.90 243.57 0.0056 399.50 1705 0.0391 400.10 4466 0.1025 400.70 12990 0.2982 399.00 487.14 0.0112 399.60 2044 0.0469 400.20 5532 0.1270 400.80 15120 0.3471 399.10 730.71 0.0168 399.70 2383 0.0547 400.30 6598 0.1515 400.90 17250 0.3960 399.20 974.29 0.0224 399.80 2722 0.0625 400.40 7664 0.1759 401.00 19380 0.4449 1/23/92 Dodds Engineers , Incorporated page 4 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS EX DEPRESSIONS --------------------------------------------------------------------- --------------------------------------------------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 31 Description: EX. DEPRESSION EAST STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----> (ft) ---cf--- --Ac-Ft- Ift) ---cf--- --AC-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- -------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------- 402.70 0.0000 0.0000 403.30 392.50 0.0090 403.90 1568 0.0360 404.50 4126 0.0947 402.80 11.667 0.0003 403.40 511.67 0.0117 404.00 1841 0.0423 404.60 4583 0.1052 402.90 23.333 0.0005 403.50 630.83 0.0145 404.10 2298 0.0528 404.70 5040 0.1157 403.00 35.000 0.0008 403.60 750.00 0.0172 404.20 2755 0.0632 404.80 5497 0.1262 403.10 154.17 0.0035 403.70 1023 0.0235 404.30 3212 0.0737 404.90 5954 0.1367 403.20 273.33 0.0063 403.80 1296 0.0297 404.40 3669 0.0842 405.00 6411 0.1472 1/23/92 Dodds Engineers , Incorporated page 5 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS EX DEPRESSIONS --------------------------------------------------------------------- --------------------------------------------------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 40 Description: EX. DEPRESSION EAST STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- -------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------- 398.50 0.0000 0.0000 399.10 9946 0.2283 399.70 53888 1.2371 400.30 133970 3.0755 398.60 928.00 0.0213 399.20 15252 0.3501 399.80 65247 1.4979 400.40 149305 3.4276 398.70 1856 0.0426 399.30 20558 0.4719 399.90 76606 1.7586 400.50 164640 3.7796 398.80 2784 0.0639 399.40 25864 0.5938 400.00 87965 2.0194 398.90 3712 0.0852 399.50 31170 0.7156 400.10 103300 2.3714 399.00 4640 0.1065 399.60 42529 0.9763 400.20 118635 2.7235 1/23/92 Dodds Engineers , Incorporated page 6 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS EX DEPRESSIONS --------------------------------------------------------------------- --------------------------------------------------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 50 Description: EX. DEPRESSION EAST STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----) STAGE (----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- -------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------- 399.00 0.0000 0.0000 400.20 3008 0.0691 401.40 12536 0.2878 402.60 25760 0.5914 399.10 142.00 0.0033 400.30 3802 0.0873 401.50 13330 0.3060 402.70 27170 0.6237 399.20 284.00 0.0065 400.40 4596 0.1055 401.60 14124 0.3242 402.80 29303 0.6727 399.30 426.00 0.0098 400.50 5390 0.1237 401.70 14918 0.3425 402.90 31435 0.7216 399.40 568.00 0.0130 400.60 6184 0.1420 401.80 15712 0.3607 403.00 34520 0.7925 399.50 710.00 0.0163 400.70 6978 0.1602 401.90 16506 0.3789 403.10 37605 0.8633 399.60 852.00 0.0196 400.80 7772 0.1784 402.00 17300 0.3972 403.20 40690 0.9341 399.70 994.00 0.0228 400.90 8566 0.1966 402.10 18710 0.4295 403.30 43775 1.0049 399.80 1136 0.0261 401.00 9360 0.2149 402.20 20120 0.4619 403.40 46860 1.0758 399.90 1278 0.0293 401.10 10154 0.2331 402.30 21530 0.4943 403.50 49945 1.1466 400.00 1420 0.0326 401.20 10948 0.2513 402.40 22940 0.5266 400.10 2214 0.0508 401.30 11742 0.2696 402.50 24350 0.5590 3. EXISTING UPSTREAM OFFSITE HYDROLOGY All of the drainage analysis has been completed with the use of the "Waterworks" hydrology program. The program utilizes the SCS-Santa Barbara Urban Hydrograph method to create and route hydrographs. A total of 114.2 acres of offsite area are tributary to this site. This offsite basin has been divided into 7 separate sub-basins for this analysis. a. WEST BASIN ('OW'): This basin contributes runoff to the drainage channel which flows through the west portion of the site. It is approximately 46.5 acres and consists mainly of undeveloped land and the Honeydew School's playfield. Area = 46.5 ac (0.2 ac, hydrologic group "D", 46.3 ac, "C") 10.0 ac, residential [15 DU/ac,20% impervious] 2.0 ac @ CN = 98, 8.0 ac @ CN = 86 (landscaping) 3.0 ac, pasture -- CN = 85 10.1 ac, school 1.1 ac impervious -- CN = 98 0.2 ac landscape (hyd. group "D") -- CN = 90 8.8 ac landscape (hyd. group "C") -- CN = 86 23.4 ac, forested -- CN = 76 TOTALS: impervious = 3.1 ac @ CN = 98; pervious = 43.4 ac @ CN = 80.6 Time of Concentration: (calculated by"Waterworks"program) 200', sheet flow over grass, slope = 1% 100', sheet flow over grass, slope = 4% 500', shallow flow over grass/brush, slope = 4% 400', shallow flow over brush/trees, slope = 1.5% 800', defined forest channel, slope = 0.5% Tc = 72.2 minutes b. EAST BASINS: The remaining 6 basins are all within the east drainage basin. They total 67.7 acres which are approximately 60% developed. Three of these basins (24.4 acres) release runoff into a roadside ditch along Duvall Avenue. This water does not actual flow through the site, except where the ditch is located outside of the road right-of-way. These basins ("03", "04" and "06") will be intercepted by the proposed tight-line system in Duvall Avenue, which will allow the filling of the existing ditch, as required to widen Duvall Avenue. "O1": Area = 18.6 acres, tributary to existing onsite depressions 8.0 ac, residential/pasture [18% impervious] 1.4 ac impervious @ CN = 98 6.6 ac landscape/pasture @ CN = 85.5 0.5 ac, additional road @ CN = 98 2.0 ac, brush @ CN = 81 8.1 ac, forest @ CN = 76 TOTALS: impervious = 1.9 ac @ CN = 98; pervious = 16.7 ac @ CN = 80.3 Time of Concentration: 300', sheet flow - brush/trees, slope = 8% 550', shallow flow- grass, slope = 1.8% 80', pipe, slope approx. 2% 400', defined forest channel, slope = 2.5% 550', defined forest channel, slope = 1% Tc = 57.4 minutes "02": Area = 11.5 acres, tributary to existing onsite depressions 11.0 ac, residential [1.5 DU/ac, 20% impervious] 2.2 ac, impervious @ CN = 98 8.8 ac, landscape/brush/trees @ CN = 81 0.5 ac, roadway @ CN = 98 TOTALS: impervious, 2.7 ac @ CN = 98; pervious, 8.8 ac @ CN = 81 Time of Concentration: 300', sheet flow - grass/brush, slope = 6% 350', shallow flow - grass/brush, slope = 5.7% 600', grass/diet channel, slope = 1% 80', pipe, slope approx 2% Tc = 39.3 minutes "03": Area = 6.9 acres, tributary to Duvall Ave. ditch 6.4 ac, residential [3 DU/ac, 34% impervious] 2.2 ac impervious @ CN = 98 4.2 ac, brush/grass/trees @ CN = 81 0.5 ac, roadway @ CN = 98 TOTALS: impervious, 2.7 ac @ CN = 98; pervious, 4.2 ac @ CN = 81 Time of Concentration: 300', sheet flow - grass, slope = 6.5% 400', grass/dirt channel, slope = 6% 300', grass/dirt channel, slope = 4% 80', pipe, slope approx. 2% Tc = 35.7 minutes "04": Area = 16.5 acres, tributary to Duvall Ave. ditch 4.6 ac, residential [3 DU/ac,34% impervious] 1.6 ac, impervious @ CN = 98 3.0 ac, brush/grass @ CN = 83 0.8 ac, road @ CN = 98 2.0 ac, brush @ CN = 81 9.1 ac, forest @ CN = 76 TOTALS: impervious, 2.4 ac @ CN = 98; pervious, 14.1 ac @ CN = 78.2 Time of Concentration: 200', sheet flow - grass, slope = 2.5% 650', grass/dirt channel, slope = 2% 250', grass/dirt channel, slope = 10% 570', defined forest channel, slope = 6% Tc = 48.9 minutes "05": 13.2 acres, tributary to onsite SW wetland 2.0 ac, residential [2 DU/ac,25% impervious] 0.5 ac, impervious @ CN = 98 1.5 ac, landscaping @ CN = 86 4.0 ac, brush @ CN = 81 7.2 ac, forest @ CN = 76 TOTALS: impervious, 0.5 ac @ CN = 98; pervious, 12.7 ac @ CN = 78.8 Time of Concentration: 280', sheet flow- grass/brush, slope = 5% 800', shallow flow - forest/brush, slope 6.8% Tc = 44.3 minutes "06": 1.0 acres, tributary to Duvall Ave. ditch 0.9 ac, impervious road @ CN = 98 0.1 ac, gravel shoulders @ CN = 89 Time of Concentration: 30', sheet flow- pavement, slope = 2% 650', grass/dirt channel, slope = 0.4% Tc = 10.7 minutes Basin summary printouts are attached. =S, d =, � ,'•I.r ,!I' '�.111 ., 1�� ' • •�` II Y TA. .� ,;_• .r f •, I • t; .+ � :11 :; .., f`•i;i �:.• f 011 MId!••' { ;r N�,. R r,' 11• ,Ip =I(i1!:f t`• f 1 tl �- II ,' 1 I •' }; II I 11 419 O h 1� •11 ti �,,i y 0 I 1 1 ,I O M 1 .f Ll in in 41.1 _J •ao 461 1 ' yl • �..�aa 1 141 n ■U f n CJt �� 411 O ^ I � � � � ` ram I :'a• .O � r '�: '� �.��!�5: ..I �r �r�►t�ll7 �lil 494 . -s•n 1. 'X 4of J 1 I III dpgtl°t• c�clt• ,t1100ia. '�:• i. 1.� ;,�' I "j/Jf _.�I 59t 410 {:': = Itt•. , • .,,. 1. `�•-� �� LEI ' r .i... .j'a its, - - '•-rj-:' " -' ' •J' 1 L r I ./�f: 11 i 'll ';•i !li S � ;: ., :�1 •OI -. �' .....j:..i.... .:4 1. 1 �•'• ' ° p __ II II,, 1 J • r r 411 u= lac,l'.i jC•� T [, I �• 1 �j - ! I OD .AJIJI��rJI - SV Lai YI JP onto or f/r��Pf of iz,� r. • �,s, IJ ti`i •M . , ...• 1 l J ' U 1I•x �y - 41! , \.=/ ''' 1; 'i�1•.\•. }I; • I' ' '. I-I I I to 401 , .,. •�. ..r;F'i . 71,. .��,� ..... � '.11;1,1:��,�!'.:'ll 't, r, (� tl l• fact! r/� \ _ Ij„I:;./J `• 'j' _• 0 V f I �_ ---___ �_ Q'1 lu �•'� ' ,�,.. � --- �-•!�I,iy 1. i 'r ;••• .�rA•I.• 'r�, ,`, .�. w (�-- ;� 1 to 'iI'I L�:tT.{�fs>arnf• .. I+ , w�� _�,',,-r J� ' ',. v �• fall,1,, ' .p o Ertl ;. U-�"�., •a It. j •� :'�r�=•; •:' ,r :',j:b , /'I I I ••-�-1L 11�wl�. .��1�+-. 'ice � ,'.1j���'�i, 'i��l.��:�.1.`3.i1•I:��j' i,)' I I •a0111 i, la. �; r D• y` r. I '1.1: 1'r.;._ rl' -',1 of 44 If oo m .•: i' `T - - -��.• �,,.,`�. ' 1 '•' 'I.;• ..•'° _--•r—Nf �LI '�1.,�� ' / II' ti�,�r,?• •a• .�,�r��=�'�'.'•i• •'i ;', •`� � 1 j'r1 4 '• �''i',atr.11 .. ' �'�I �' 1 _I ...__.._ I'l1 -y ! it ;.ij' }.4.r f"1 ,�I cc ` —41110 �; •:� {'1 00 CO Q ■� � / II / s` i '_ �-J"I- ` ° r �;� '='f�•'"!N'4I ^':: , '••' .�• ` ,1 ,00 '1 1 i O O I'� 404 ■ CO Io '�_-1'.—!'��,/' _`' r�-' �I NObUAu+l['I` I ,✓i�.J °' �` f,1 �I ' —•—� D ( ''ti'/:•oil 'I ' :5..'1. t!,.r j'�.:I,. .. :•r 1):'� , � �1 �1 71 4. . , � 1 '�`i, !.�'S.• l�:• ',.j'. .II,i'�.�.ai�r•�.I.i��hU1,Of 1.N ...�' D t' ' 1•�.'':)r V. r •f'S,1h�,Il,,.,n ,1;: �.A r.f=IY 1' 3/• 4.11''111'M ..� trts : � 'Ad/rlrplirtUoh No!•{f-1)-d'�: 'l 1'. '1: .r nnln[cruf �' lid .1.:j:�i.k.III 1Mi,1 r . j ,��!�'11), •: M,,. V/ r oiorhbnl o/S.cGaiti:...•i 1) .' .., '. ' 1'f��i. 1 �7 i,hgl.cf/•11. +!' q i l'1,4.• •.:.._4.....1_r».ff .( l 1 ►t /• • .i!' 1'poitl.npul.r prl/l D.�d bn Ilir{III 1 i'i 1�;.` f ;•a.1......_ i.. rod d of 1 .R al;�UhAlnprwi�id.111 1e.,. .. ._.:�' . .. --_. 7 4. DEVELOPED SITE HYDROLOGY As previously discussed, the developed drainage system will continue to split the site into two drainage basins. a. WEST BASIN: The proposed design for the west basin involves the use of the existing wetland #1 for detention. Due to site constraints, a developed area slightly less than the existing west basin will be tributary to the detention system. The remaining area will be directed to the main east detention pond, but the developed discharges will be designed to match the existing peak flows of either basin. "Z": 13.6 acres, tributary to main west detention system (100) 4.70 ac, impervious @ CN =98 7.20 ac,landscaping/wetland/brush @ CN = 84.5 Time of Concentration: estimated at 25 minutes b. EAST BASIN: The developed east basin will be divided into three sub-basins, each tributary to one of the enhanced wetlands to be used for storm drainage detention/water quality facilities. "W: 2.80 acres, tributary to the southeast detention system (300) 1.22 ac, impervious @ CN =98 1.60 ac, landscape/brush @ CN = 85 Time of Concentration: estimated at 20 minutes "W": 8.1 acres, tributary to the second wetland (400) 3.6 ac, impervious @ CN =98 4.5 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 25 minutes "X": 14.52 acres, tributary to the first wetland (200) 4.72 ac, impervious @ CN = 98 9.8 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes "Y": 23.3 acres, tributary to the third wetland (300) 10.4 ac, impervious @ CN = 98 12.9 ac, landscaping/brush/wetland @ CN = 85 Time of Concentration: estimated at 30 minutes A developed drainage map is included in this section along with Basin Summary printouts and basin flow summaries. - - - �G�� ` 1 .. •I 1 13 16 ', 17 is a •i 20 2F 1_.� Y223 33 `�..�,2 I - ��' � /2—� I-•I^I3 �I� N /i.'I '�• 3 3C_ 4 \ � �/ I � i��, iio J'\� ,\`�r, 7 'll1 Iz Ag 1 y1 1 2 -� �. ;I ° ` ` (E'nc+ r.-- .! try . `,, \ " _- �� •�l r� �"'• J••••IIII• �tl .I 8 ;' :�t(B ( �� r�^f `` ��r� '11 •3/1 is Y .. ,•�: 9 �a d I y Ej I I I '�� .�'�� / . � I � ',• \� t � -_=.--ter•` ��' "81� 13 i N 13 I 12 I B I to \\ 3 •q / i 61�. 83 } ,IF a;_ i... _ ;.o 71 QQ43 74 76 77 7e /79" ? eo I e1 ;�ag� 9Y\ ``ar } t i p n`.k � �• � S 9Q'� e9 ar` 'ec p � tj 98 {I 99 �" 100 't !'i •.'ram ! 8 )�'.°I ,�'•` I .r Leo�. _� �� I i � try� i-1.t•z ti r" �/�.� � i i #� � w C• „ ,IVj �� '`1' ���` �1- h-� III . .... 4 —�• 1III / ._ •-. /I �J �i I �: 300 1'1M 1 1t DEVELOPED ONSITE BASINS 71 DEI #88008 / THE ORCHARDS x BB•n>'�•w ' 2/5/92 BY:GRS 4/ 4/94 Dodds Engineers, Incorporated page 1 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS BASIN RESULT SUMMARY BASIN -----VOLUME---- -RATE- ----TIME----- Hydrograph Area ID ---cf-- Ac-ft --cfs- -min- hours Methodology Acres Al-A 26999 0.62 0.76 490 8.17 SBUH Method 10.70 Al-A2 16070 0.37 0.35 520 8.67 SBUH Method 10.70 Al-B 54627 1.25 1.92 490 8.17 SBUH Method 10.70 Al-C 87113 2.00 3.34 490 8.17 SBUH Method 10.70 Al-D 247232 5.68 2.61 3360 56.00 SBUH Method 10.70 A2-A 3028 0.07 0.11 480 8.00 SBUH Method 1.20 A2-A2 1802 0.04 0.05 490 8.17 SBUH Method 1.20 A2-B 6126 0.14 0.28 480 8.00 SBUH Method 1.20 A2-C 9770 0.22 0.49 480 8.00 SBUH Method 1.20 A2-D 27730 0.64 0.33 3300 55.00 SBUH Method 1.20 B-A 1975 0.05 0.07 480 8.00 SBUH Method 0.90 B-A2 1131 0.03 0.03 490 8.17 SBUH Method 0.90 B-B 4166 0.10 0.20 480 8.00 SBUH Method 0.90 B-C 6794 0.16 0.36 480 8.00 SBUH Method 0.90 B-D 19565 0.45 0.24 3300 55.00 SBUH Method 0.90 C-A 6603 0.16 0.24 480 8.00 SBUH Method 3.10 C-A2 3897 0.09 0.09 490 8.17 SBUH Method 3.10 C-B 14350 0.33 0.67 480 8.00 SBUH Method 3.10 C-C 23401 0.54 1.21 480 8.00 SBUH Method 3.10 C-D 67386 1.55 0.81 3300 55.00 SBUH Method 3.10 D-A 7022 0.16 0.16 520 8.67 SBUH Method 3.20 D-A2 4022 0.09 0.08 760 12.67 SBUH Method 3.20 D-B 14812 0.34 0.44 490 8.17 SBUH Method 3.20 D-C 24156 0.55 0.80 490 8.17 SBUH Method 3.20 D-D 69542 1.60 0.71 3360 56.00 SBUH Method 3.20 E-A 5486 0.13 0.15 490 8.17 SBUH Method 2.50 E-A2 3142 0.07 0.06 520 8.67 SBUH Method 2.50 E-B 11572 0.27 0.43 490 8.17 SBUH Method 2.50 E-C 18872 0.43 0.77 490 8.17 SBUH Method 2.50 E-D 54330 1.25 0.59 3300 55.00 SBUH Method 2.50 F-A 24556 0.56 0.57 520 8.67 SBUH Method 10.80 F-A2 14205 0.33 0.27 760 12.67 SBUH Method 10.80 F-B 51248 1.18 1.55 490 8.17 SBUH Method 10.80 F-C 83101 1.91 2.81 490 8.17 SBUH Method 10.80 F-D 238382 5.47 2.45 3360 56.00 SBUH Method 10.80 G-A 18763 0.43 0.36 640 10.67 SBUH Method 8.55 G-A2 10747 0.25 0.20 760 12.67 SBUH Method 8.55 G-B 39577 0.91 0.96 520 8.67 SBUH Method 8.55 G-C 64541 1.48 1.75 500 8.33 SBUH Method 8.55 G-D 185809 4.27 1.78 3360 56.00 SBUH Method 8.55 H-A 19821 0.46 0.58 490 8.17 SBUH Method 7.70 H-A2 11900 0.27 0.27 500 8.33 SBUH Method 7.70 H-B 39787 0.91 1.44 490 8.17 SBUH Method 7.70 H-C 63224 1.45 2.47 490 8.17 SBUH Method 7.70 H-D 179037 4.11 1.90 3300 55.00 SBUH Method 7.70 I-A 8421 0.19 0.17 1440 24.00 SBUH Method 9.17 4/ 4/94 Dodds Engineers, Incorporated page 2 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS BASIN RESULT SUMMARY BASIN -----VOLUME---- -RATE- ----TIME----- Hydrograph Area ID ---cf-- Ac-ft --cfs- -min- hours Methodology Acres I-A2 3547 0.08 0.09 1440 24.00 SBUH Method 9.17 I-B 23602 0.54 0.46 520 8.67 SBUH Method 9.17 I-C 44207 1.01 1.18 500 8.33 SBUH Method 9.17 I-D 138324 3.18 1.27 3360 56.00 SBUH Method 9.17 J-A 9875 0.23 0.27 490 8.17 SBUH Method 4.50 J-A2 5656 0.13 0.11 520 8.67 SBUH Method 4.50 J-B 20830 0.48 0.76 490 8.17 SBUH Method 4.50 J-C 33969 0.78 1.38 490 8.17 SBUH Method 4.50 J-D 97794 2.25 1.06 3300 55.00 SBUH Method 4.50 01-A 47088 1.08 1.22 500 8.33 SBUH Method 18.60 01-A2 28915 0.66 0.62 500 8.33 SBUH Method 18.60 01-C 148319 3.40 5.17 490 8.17 SBUH Method 18.60 01-D 420256 9.65 4.30 3360 56.00 SBUH Method 18.60 02-A 35003 0.80 1.24 490 6.17 SBUH Method 11.50 02-A2 22746 0.52 0.72 490 8.17 SBUH Method 11.50 02-A3 4496 0.10 0.18 480 8.00 SBUH Method 11.50 02-C 100466 2.31 4.26 480 8.00 SBUH Method 11.50 02-D 278901 6.40 3.05 3300 55.00 SBUH Method 11.50 03-A 26607 0.61 1.11 480 8.00 SBUH Method 6.90 03-A2 16405 0.42 0.73 480 8.00 SBUH Method 6.90 03-A3 4898 0.11 0.22 480 8.00 SBUH Method 6.90 03-C 68117 1.56 3.11 480 8.00 SBUH Method 6.90 03-D 183974 4.22 2.05 3300 55.00 SBUH Method 6.90 04-A 41214 0.95 1.16 490 8.17 SBUH Method 16.50 04-A2 25648 0.59 0.62 490 8.17 SBUH Method 16.50 04-A3 4406 0.10 0.17 490 8.17 SBUH Method 16.50 04-C 128840 2.96 4.76 490 8.17 SBUH Method 16.50 04-D 365259 8.39 3.74 3360 56.00 SBUH Method 16.50 05-A 26949 0.62 0.65 500 8.33 SBUH Method 13.20 05-A2 15400 0.35 0.28 760 12.67 SBUH Method 13.20 05-A3 1147 0.03 0.04 480 8.00 SBUH Method 13.20 05-C 94689 2.17 3.57 490 8.17 SBUH Method 13.20 05-D 274452 6.30 2.85 3300 55.00 SBUH Method 13.20 06-A 5947 0.14 0.41 480 8.00 SBUH Method 1.00 06-A2 4452 0.10 0.31 480 8.00 SBUH Method 1.00 06-C 12755 0.29 0.86 480 8.00 SBUH Method 1.00 06-D 32754 0.75 0.42 3300 55.00 SBUH Method 1.00 08-B 36690 0.84 1.36 490 8.17 SBUH Method 7.00 08-C 58059 1.33 2.33 490 8.17 SBUH Method 7.00 OW-A 112519 2.58 2.54 520 8.67 SBUH Method 46.50 OW-A2 67655 1.55 1.24 530 8.83 SBUH Method 46.50 OW-A3 7505 0.17 0.19 490 8.17 SBUH Method 46.50 OW-C 364402 8.37 11.23 490 8.17 SBUH Method 46.50 OW-D 1037846 23.83 10.31 3360 56.00 SBUH Method 46.50 V-A 12347 0.28 0.68 480 8.00 SBUH Method 2.80 V-B 20823 0.48 1.20 480 8.00 SBUH Method 2.80 4/ 4/94 Dodds Engineers, Incorporated page 3 DRAINAGE ANALYSIS THE ORCHARDS -- 88008 " ------------------ BASIN RESULT SUMMARY BASIN -----VOLUME---- -RATE- ----TIME----- Hydrograph Area ID ---cf-- Ac-ft --cfs- -min- hours Methodology Acres V-C 30199 0.69 1.76 480 8.00 SBUH Method 2.80 V-D 80439 1.85 0.99 3300 55.00 SBUH Method 2.80 W-A 36176 0.83 1.86 480 8.00 SBUH Method 8.10 W-B 60784 1.40 3.23 480 8.00 SBUH Method 8.10 W-C 87970 2.02 4.77 480 8.00 SBUH Method 8.10 W-D 233935 5.37 2.81 3300 55.00 SBUH Method 8.10 X-A 58687 1.35 2.71 480 8.00 SBUH Method 14.52 X-B 101586 2.33 4.96 480 8.00 SBUH Method 14.52 X-C 149501 3.43 7.52 480 8.00 SBUH Method 14.52 X-D 402261 9.23 4.71 3300 55.00 SBUH Method 14.52 Y-A 104219 2.39 4.98 480 8.00 SBUH Method 23.30 Y-B 175038 4.02 8.68 480 8.00 SBUH Method 23.30 Y-C 253258 5.81 12.80 480 8.00 SBUH Method 23.30 Y-D 673258 15.46 7.86 3300 55.00 SBUH Method 23.30 Z-A 55122 1.27 2.69 480 8.00 SBUH Method 13.60 Z-B 95180 2.19 4.89 480 8.00 SBUH Method 13.60 Z-C 139950 3.21 7.39 480 8.00 SBUH Method 13.60 Z-D 376407 8.64 4.49 3300 55.00 SBUH Method 13.60 5. HYDROLOGIC ANALYSIS The City of Renton storm drainage detention requirements for this project are as follows: 1) Match the existing peak runoff rate of the 1/2 2yr, 24hr storm, for the 2yr, 24hr storm event in the developed condition. 2) Match the existing peak runoff rate of the 2yr, 24hr storm, for the 10yr, 24hr storm event in the developed condition. 3) Match the existing peak runoff rate of the 100yr, 24hr storm, for the 100yr, 24hr storm event in the developed condition. 4) Match the existing peak runoff rate of the 100yr, 7day storm, for the 100yr, 7day storm event in the developed condition. The computer modeling for each storm involves creating hydrographs for each basin during each storm event. To do this, the program requires that each basin and storm combination be defined as a "basin" with an identification label. These labels have been designated using the basin numbers or letters previously described (i.e. OW, A, X, 05) followed by a letter code for each storm event: "A" = 2yr, 24hr storm (2.00" of precipitation, from NOAA maps) "B" = 10yr, 24hr storm(2.95" of precipitation) "C" = 100yr, 24hr storm (3.95" of precipitation) "D" = 100yr, 7day storm (9.90" of precipitation) "A2" = 1/2 2yr, 24hr storm (1.56" of precipitation, determined by trials to produce a peak= 1/2 the 2yr peak) By this method, the label "Y-B" is the 10yr storm runoff for the "Y" basin. ROUTING PROCEDURE: Schematics of the routing procedures for the existing and developed conditions for the west and east basins are included in this section. The routing involves a number of possible actions, as described below: 1) "Move" a basin to a hydrograph number. 2) "Add" hydrographs. 3) Combine a number of basin hydrographs. 4) "Divert" (subtract) a flow amount, or percentage of the flow, from a hydrograph. 5) Route a hydrograph through a storage and discharge structure. Program code for all of these steps has been written to direct the Waterworks program through all of the steps necessary for the various conditions. Printouts of these "programs" are included in the appendix. PROGRAM SUMMARIES: a. ** Existing West Basin ** 1) Combine basins "OW" and "A2" = HG(hydrograph) #6 2) Route HG#6 through existing depression "10"; Discharge =HG#7 3) Add basin "A1" and "J" to HG#7 =TOTAL DISCHARGE listed below 4) For 1/2 2yr, "divert" 50% of total 2yr discharge to get 1/2 2yr peak HG#1 = Ex. 1/2 2yr discharge hydrograph HG#2 =Ex. 2yr discharge hydrograph HG#3 =Ex. 100yr, 24hr discharge hydrograph HG#4 =Ex. 100yr, 7day discharge hydrograph ** Developed West Basin ** 1) Move "OW" to HG#17. 2) Combine basin "Z" with HG#17 =HG#18. 3) Route HG#18 through storage facility "100"; Discharge =HG#13, 14, 15 or 16. 4) Add storage discharge HG and bypass HG =TOTAL DISCHARGE listed below: HG#5 =Dev. 2yr discharge =HG#13 +HG#9 HG#6 =Dev. 10yr discharge =HG#14 +HG#10 HG#7 =Dev. 100yr, 24hr discharge = HG#15 +HG#11 HG#8 =Dev. 100yr, 7day discharge =HG#16 +HG#12 NOTE: For the developed 2yr routing, the 1/2 2yr offsite basin was used with the 2yr onsite basins. Similarly, for the developed 10yr routing, the 2yr offsite basin was used with the 10yr onsite basins. Since the routing for these two storms involves matching a smaller storm event peak, this method of analysis has to be incorporated in order to avoid needlessly detaining flows from all of the offsite areas. Also, these upstream offsite areas will eventually be developed and held to the same detention requirements as this site, so this approach will better model future drainage patterns. b. ** Existing East Basins ** 1) Move basin "E" to HG#6. 2) Route HG#6 through Existing depression "50"; Discharge =HG#7. 3) Combine basins "01", "F" and HG#7 =HG#8. 4) Route HG#8 through Existing depression "40"; Discharge =HG#9. 5) Combine basins "02" and "B" =HG#10. 6) Route HG#10 through Existing depression "31"; Discharge =HG#11. 7) Add basin "C" and HG#11 =HG#12. 8) Route HG#12 through Existing depression "30"; Discharge =HG#13. 9) Combine basin "D", HG#9 and HG#13 =HG#14. 10) Route HG#14 through Existing depression "20"; Discharge =HG#15. 11) Add basins "03", "G" and HG#15 =HG#16. 12) Combine basins "04", 1105", "I" and HG#16 =HG#17. 13) Add basins "H", "06" and HG#17 =HG#1, 2, 3 or 4 (depending on the storm). TOTAL DISCHARGE HYDROGRAPHS: HG#1 =Ex. 1/2 2yr discharge hydrograph HG#2 =Ex. 2yr discharge hydrograph HG#3 =Ex. 100yr, 24hr discharge hydrograph HG#4 =Ex. 100yr, May discharge hydrograph NOTE: 1/2 2yr routing uses "-A2" basins throughout and the 2yr routing uses "-A" basins. ** Developed East Basins ** 1) Combine basins "O1", "02" and "X" =HG#17. 2) Route HG#17 through storage structure "200"; Discharge =HG#18. 3) Add basin "W" and HG#18 =HG#18. 4) Route HG#18 through storage structure "400"; Discharge =HG#19. 5) Combine basins "05", "Y", "V", and HG#19 =HG#20. 6) Route HG#20 through storage structure "300"; Discharge =HG#9, 10, 11 or 12. 7) Combine bypass basins "03", "04" and "06" =HG#13, 14, 15 or 16 8) Add discharges to obtain TOTAL DISCHARGE listed below: HG#5 =Dev. 2yr discharge hydrograph =HG#9 + HG#13 HG#6 =Dev. 10yr discharge hydrograph =HG#10 +HG#14 HG#7 =Dev. 100yr, 24hr discharge hydrograph =HG#11 + HG#15 HG#8 =Dev. 100yr, 7day discharge hydrograph =HG#12 +HG#16 See note on the previous page for the onsite and offsite storm events used for the developed routing procedure. OFFSITE TRIBUTARY FLOW CHECK Per the KCSWD Manual, offsite flows may be routed through the onsite detention system if the peak offsite 100-year flow rate is equal to or less than 50% of the peak developed 100-year flow rate for the onsite basin. The printout below shows a comparison of the combined offsite flows (01, 02, 05) in hydrograph #2 and the combined onsite developed flows (V, W, Y, Z) in hydrograph #1. Since the offsite peak is less than 50% of the onsite peak, these basins will be allowed to flow through the detention system. The west basin design allows the offsite runoff to flow through the wetland/detention pond even though the flows exceed the limits described above. Given the difficulty in bypassing the pond system and the need for recharge water to maintain the wetland, the City of Renton staff has approved this proposed layout. PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf-AcFt Acres --------------------------------------------- --------------------------------------------- 1 25 . 972 480 497022 cf 46. 12 2 12 . 969 490 343474 cf 43 . 30 ®! D O D D S ENGINEERS, INC. JOB N S � CIVIL E NGI N E ER I N G S U R V E Y I N G P L A N N I N G DATE 23 4205 148TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 [20BJ B85-7B77 OR 454-3743 B Y Lei P��L1M/N�iZY SJ A?tiR� �i5 E Xr S? 5A'�5 I 04 OZ 0 C D I 'T`rQ V , N , Z dW.wa/7 Z I� r3 = 10/Z4 2,95" o� 1Z2,Z, "0, 7 Al SHEET I OF 2 ® � D D D D S ENGINEERS, INC. .J O S NO. e�CO& CIVIL E INGINEERING S U R V E Y I N G P L A N N I N G n 4205 146TH AVE. N.E.. SUITE 200 - BELLEVUE, WA 96007 DATE gift 1_�7I Z���.� 1206) BB5-7677 OR 454-3743 E Y gi S 04- 05 0(p I3 yL z bZ 05 , ►4 Z 15 i00 Irv- ►�I7 y Zao 10 o !i -loo 10 -10 7-100 X I �-1Cr�J7 (p- 10 7 � �ao D1��Z i 7 ?SHEET OF DDDDS ENGINEERS, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G R L A N N I N G OAT E 4205 14BTH AVE. N.E., SUITE 200 - BELLEVUE, WA 56007 (206) 8B5-7B77 OR 454-3743 B Y YyS7'�)7 LEVEL POOL TABLE SUMMARY MATCH INFLOW -STO- -DIS- <-PEAK-> STORAGE <--------DESCRIPTION---------> (cfs) (cfs) --id- --id- <-STAGE> id VOL (cf) DEV WEST 2YR ................. 1.72 3.67 100 110 396.79 5 21166.70 DEV WEST 10YR ................ 3.44 7.11 100 110 397.45 6 35644.43 DEV WEST 100YR ............... 16.13 18.09 100 110 398.47 7 62389.85 DEV WEST 100YR,7DAY .......... 13.40 14.20 100 110 398.50 8 63508.57 HYDROGRAPH SUMMARY PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf-AcFt Acres --------------------------------------------- --------------------------------------------- 1 1 . 720 540 72677 cf 62 . 90 2 3 . 440 540 145353 cf 62 . 90 3 16. 128 500 488186 cf 62 . 90 4 13 . 396 3360 1403144 cf 62 . 90 5 1 . 687 930 122774 cf 60 . 10 6 3 . 395 780 207699 cf 60 . 10 7 12 . 338 560 504385 cf 60 . 10 8 12 .547 3420 1414844 cf 60 . 10 10 3 . 672 480 122777 cf 60 . 10 11 7 . 105 480 207699 cf 60 . 10 12 18 . 087 490 504352 cf 60 . 10 13 14 . 199 3360 1414253 cf 60 . 10 SHEET OF ® D O D O S ENGINEERS, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G DAT E 4205 146TH AVE. N.E.. SUITE 200 - BELLEVUE. WA 96007 [2061 6B5-7B77 OR 454-3743 B Y ROUTING COMPARISON TABLE MATCH INFLOW STO DIS PEAK PEAK OUT DESCRIPTION PEAK PEAK No. No. STG OUT HYD ---------------------------------------------------------------------- ---------------------------------------------------------------------- POND #1, 2YR 2.22 3.97 200 210 399.59 1.52 18 POND #3, 2YR 2.22 2.42 400 400 397.26 1.95 19 POND #2, 2YR 2.22 7.00 300 310 394.27 1.14 9 POND #3, 10YR 2.22 4.25 400 400 398.21 4.03 19 POND #2, 10YR 4.10 12.19 300 310 395.10 3.29 10 POND #3, 100YR 2.22 12.31 400 400 398.84 11.98 19 POND #2, 100YR 23.27 21.35 300 310 395.48 11.86 11 POND #1, 100YR-7D 19.46 11.91 200 210 400.17 10.62 18 POND #3, 100YR-7DAY 2.22 11.87 400 400 398.81 11.61 19 POND #2, 100YR-7D 19.46 18.64 300 310 395.61 16.02 12 PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf-AcFt Acres 1 2 .221 1440 132389 cf 113 . 62 2 4 . 095 490 239044 cf 113 . 62 3 23 .274 520 829896 cf 113 . 62 4 19 . 459 3360 2445974 cf 113 . 62 5 2 .217 480 212560 cf 116. 42 6 4 . 038 1440 369605 cf 116. 42 7 14 .567 840 895085 cf 116. 42 8 18 . 418 3480 2945489 cf 116. 42 SHEET OF 4/ 4/94 Dodds Engineers, Incorporated page 5 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS STAGE STORAGE TABLE CUSTOM STORAGE ID No. 100 Description: WEST WETLANDS/DETN STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- 395.24 0.0000 0.0000 396.50 15401 0.3536 397.80 43676 1.0027 399.10 81527 1.8716 395.30 6.0000 0.0001 396.60 17356 0.3984 397.90 45989 1.0558 399.20 84547 1.9409 395.40 16.000 0.0004 396.70 19311 0.4433 398.00 48301 1.1088 399.30 87568 2.0103 395.50 951.00 0.0218 396.80 21266 0.4882 398.10 51322 1.1782 399.40 90588 2.0796 395.60 1886 0.0433 396.90 23221 0.5331 398.20 54342 1.2475 399.50 93609 2.1490 395.70 2821 0.0648 397.00 25176 0.5780 398.30 57363 1.3169 399.60 96629 2.2183 395.80 3756 0.0862 397.10 27489 0.6310 398.40 60383 1.3862 399.70 99650 2.2876 395.90 4691 0.1077 397.20 29801 0.6841 398.50 63404 1.4555 399.80 102670 2.3570 396.00 5626 0.1292 397.30 32114 0.7372 398.60 66424 1.5249 399.90 105691 2.4263 396.10 7581 0.1740 397.40 34426 0.7903 398.70 69445 1.5942 400.00 108711 2.4957 396.20 9536 0.2189 397.50 36739 0.8434 398.80 72465 1.6636 396.30 11491 0.2638 397.60 39051 0.8965 398.90 75486 1.7329 396.40 13446 0.3087 397.70 41364 0.9496 399.00 78506 1.8022 4/ 4/94 Dodds Engineers, Incorporated page 1 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS STAGE STORAGE TABLE CUSTOM STORAGE ID No. 200 Description: NORTH/EAST WETLAND/DETN STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --AC-Ft- (ft) ---cf--- --AC-Ft- (ft) ---cf--- --Ac-Ft- 398.70 0.0000 0.0000 399.60 28546 0.6553 400.50 101107 2.3211 401.40 184548 4.2366 398.80 1129 0.0259 399.70 35097 0.8057 400.60 110378 2.5339 401.50 193820 4.4495 398.90 2258 0.0518 399.80 41648 0.9561 400.70 119650 2.7468 401.60 203091 4.6623 399.00 3387 0.0778 399.90 48200 1.1065 400.80 128921 2.9596 401.70 212362 4.8752 399.10 7109 0.1632 400.00 54751 1.2569 400.90 138192 3.1725 401.80 221633 5.0880 399.20 10830 0.2486 400.10 64022 1.4697 401.00 147463 3.3853 401.90 230905 5.3008 399.30 14552 0.3341 400.20 73293 1.6826 401.10 156735 3.5981 402.00 240176 5.5137 399.40 18273 0.4195 400.30 62565 1.8954 401.20 166006 3.8110 399.50 21995 0.5049 400.40 91836 2.1083 401.30 175277 4.0238 4/ 4/94 Dodds Engineers, Incorporated page 2 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS STAGE STORAGE TABLE CUSTOM STORAGE ID No. 300 Description: STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- 390.80 0.0000 0.0000 394.60 229030 5.2578 398.50 648613 14.890 402.40 1039390 23.861 390.80 0.0000 0.0000 394.70 241635 5.5472 398.60 658337 15.113 402.50 1049938 24.103 390.90 2542 0.0583 394.80 254240 5.8365 398.70 668062 15.337 402.60 1060485 24.345 391.00 5083 0.1167 394.90 266845 6.1259 398.80 677786 15.560 402.70 1071033 24.588 391.10 7625 0.1750 395.00 279450 6.4153 398.90 687511 15.783 402.80 1081580 24.830 391.20 10167 0.2334 395.10 292055 6.7047 399.00 697235 16.006 402.90 1092128 25.072 391.30 12708 0.2917 395.20 304660 6.9940 399.10 706960 16.230 403.00 1102675 25.314 391.40 15250 0.3501 395.30 317265 7.2834 399.20 716684 16.453 403.10 1113223 25.556 391.50 17792 0.4084 395.40 329870 7.5728 399.30 726409 16.676 403.20 1123770 25.798 391.60 20333 0.4668 395.50 342475 7.8621 399.40 736133 16.899 403.30 1134318 26.040 391.70 22875 0.5251 395.60 355080 8.1515 399.50 745858 17.123 403.40 1144865 26.282 391.80 25417 0.5835 395.70 367685 8.4409 399.60 755582 17.346 403.50 1155413 26.525 391.90 27958 0.6418 395.80 380290 8.7303 399.70 765307 17.569 403.60 1165960 26.767 392.00 30500 0.7002 395.90 392895 9.0196 399.80 775031 17.792 403.70 1176508 27.009 392.10 36645 0.8413 396.00 405500 9.3090 399.90 784756 18.016 403.80 1187055 27.251 392.20 42790 0.9823 396.10 415225 9.5322 400.00 794480 18.239 403.90 1197603 27.493 392.30 48935 1.1234 396.20 424949 9.7555 400.10 804205 18.462 404.00 1208150 27.735 392.40 55080 1.2645 396.30 434674 9.9787 400.20 813929 18.685 404.10 1218698 27.977 392.50 61225 1.4055 396.40 444398 10.202 400.30 823654 18.908 404.20 1229245 28.220 392.60 67370 1.5466 396.50 454123 10.425 400.40 833378 19.132 404.30 1239793 28.462 392.70 73515 1.6877 396.60 463847 10.648 400.50 843103 19.355 404.40 1250340 28.704 392.80 79660 1.8287 396.70 473572 10.872 400.60 852827 19.578 404.50 1260888 28.946 392.90 85805 1.9698 396.80 483296 11.095 400.70 862552 19.801 404.60 1271435 29.188 393.00 91950 2.1109 396.90 493021 11.318 400.80 872276 20.025 404.70 1281983 29.430 393.10 98095 2.2520 397.00 502745 11.541 400.90 882001 20.248 404.80 1292530 29.672 393.20 104240 2.3930 397.10 512470 11.765 401.00 891725 20.471 404.90 1303078 29.915 393.30 110385 2.5341 397.20 522194 11.988 401.10 902273 20.713 405.00 1313625 30.157 393.40 116530 2.6752 397.30 531919 12.211 401.20 912820 20.955 405.10 1324173 30.399 393.50 122675 2.8162 397.40 541643 12.434 401.30 923368 21.198 405.20 1334720 30.641 393.60 128820 2.9573 397.50 551368 12.658 401.40 933915 21.440 405.30 1345268 30.883 393.70 134965 3.0984 397.60 561092 12.881 401.50 944463 21.682 405.40 1355815 31.125 393.80 141110 3.2394 397.70 570817 13.104 401.60 955010 21.924 405.50 1366363 31.367 393.90 147255 3.3805 397.80 580541 13.327 401.70 965558 22.166 405.60 1376910 31.610 394.00 153400 3.5216 397.90 590266 13.551 401.80 976105 22.408 405.70 1387458 31.852 394.10 166005 3.8110 398.00 599990 13.774 401.90 986653 22.650 405.80 1398005 32.094 394.20 178610 4.1003 398.10 609715 13.997 402.00 997200 22.893 405.90 1408553 32.336 394.30 191215 4.3897 398.20 619439 14.220 402.10 1007748 23.135 406.00 1419100 32.578 394.40 203820 4.6791 398.30 629164 14.444 402.20 1018295 23.377 394.50 216425 4.9684 398.40 638888 14.667 402.30 1028843 23.619 4/ 4/94 Dodds Engineers, Incorporated page 3 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS STAGE STORAGE TABLE CUSTOM STORAGE ID No . 400 Description: EAST WETLAND STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- 396.00 0.0000 0.0000 398.30 16780 0.3852 400.60 87300 2.0041 402.90 231050 5.3042 396.10 435.00 0.0100 398.40 18140 0.4164 400.70 93550 2.1476 403.00 237300 5.4477 396.20 870.00 0.0200 398.50 19500 0.4477 400.80 99800 2.2911 403.10 243550 5.5911 396.30 1305 0.0300 398.60 20860 0.4789 400.90 106050 2.4346 403.20 249800 5.7346 396.40 1740 0.0399 398.70 22220 0.5101 401.00 112300 2.5781 403.30 256050 5.8781 396.50 2175 0.0499 398.80 23580 0.5413 401.10 118550 2.7215 403.40 262300 6.0216 396.60 2610 0.0599 398.90 24940 0.5725 401.20 124800 2.8650 403.50 268550 6.1651 396.70 3045 0.0699 399.00 26300 0.6038 401.30 131050 3.0085 403.60 274800 6.3085 396.80 3480 0.0799 399.10 28650 0.6577 401.40 137300 3.1520 403.70 281050 6.4520 396.90 3915 0.0899 399.20 31000 0.7117 401.50 143550 3.2955 403.80 287300 6.5955 397.00 4350 0.0999 399.30 33350 0.7656 401.60 149800 3.4389 403.90 293550 6.7390 397.10 5185 0.1190 399.40 35700 0.8196 401.70 156050 3.5824 404.00 299600 6.8825 397.20 6020 0.1382 399.50 38050 0.8735 401.80 162300 3.7259 404.10 306050 7.0259 397.30 6855 0.1574 399.60 40400 0.9275 401.90 168550 3.8694 404.20 312300 7.1694 397.40 7690 0.1765 399.70 42750 0.9814 402.00 174800 4.0129 404.30 318550 7.3129 397.50 8525 0.1957 399.80 45100 1.0354 402.10 161050 4.1563 404.40 324800 7.4564 397.60 9360 0.2149 399.90 47450 1.0893 402.20 187300 4.2998 404.50 331050 7.5999 397.70 10195 0.2340 400.00 49800 1.1433 402.30 193550 4.4433 404.60 337300 7.7433 397.80 11030 0.2532 400.10 56050 1.2867 402.40 199800 4.5868 404.70 343550 7.8868 397.90 11865 0.2724 400.20 62300 1.4302 402.50 206050 4.7303 404.80 349800 8.0303 398.00 12700 0.2916 400.30 68550 1.5737 402.60 212300 4.8737 404.90 356050 8.1738 398.10 14060 0.3228 400.40 74800 1.7172 402.70 218550 5.0172 405.00 362300 8.3173 398.20 15420 0.3540 400.50 81050 1.8607 402.80 224800 5.1607 4/ 4/94 Dodds Engineers, Incorporated page 2 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS DISCHARGE STRUCTURE LIST DISCHARGE LIST ID No. 10 Description: FROM DEPRESSION WEST COMBINATION DISCHARGE ID No. 110 Description: WEST POND Structure: 160 Structure: Structure: 161 Structure: Structure: 162 MULTIPLE ORIFICE ID No. 160 Description: WEST POND Outlet Elev: 395 .24 Elev: 393 .24 ft Orifice Diameter: 7 . 0000 in. RISER DISCHARGE ID No. 161 Description: WEST POND Riser Diameter (in) : 15 . 00 elev: 397 .50 ft Weir Coefficient . . . : 3 . 782 height : 399 . 00 ft Orif Coefficient . . . : 9. 739 increm: 0 . 10 ft NOTCH WEIR ID No. 162 Description: west pond Weir Length: 0 . 8333 ft . Weir height (p) : 1 . 4000 ft . Elevation : 396. 75 ft . Weir Increm: 0 . 10 DISCHARGE LIST ID No. 20 Description: FROM DEPRESSION 20, EAST BROAD CRESTED WEIR ID No. 200 Description: POND 2 OVERFLOW cd: 3 . 0300 Weir length: 0 . 6000 ft . El : 398 . 70 ft . Weir Increm: 0 . 10 COMBINATION DISCHARGE ID No. 210 Description: Structure: 200 Structure : Structure: 220 Structure : Structure: BROAD CRESTED WEIR ID No. 220 Description: POND 2 OVERFLOW cd: 3 . 0300 Weir length: 7 . 6000 ft . E1 : 399.70 ft . Weir Increm: 0 . 10 4/ 4/94 Dodds Engineers, Incorporated page 3 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS DISCHARGE STRUCTURE LIST DISCHARGE LIST ID No . 30 Description: FROM DEPRESSION 30, EAST MULTIPLE ORIFICE ID No. 300 Description: SOUTH POND Outlet Elev: 390 . 80 Elev: 388 . 80 ft Orifice Diameter: 4 . 7500 in. NOTCH WEIR ID No. 301 Description: Weir Length: 1 . 0000 ft . Weir height (p) : 3 . 0000 ft . Elevation : 394 . 30 ft . Weir Increm: 0 . 10 RISER DISCHARGE ID No . 303 Description: Riser Diameter (in) : 18 . 00 elev: 395 . 10 ft Weir Coefficient . . . : 3 . 782 height : 406. 00 ft Orif Coefficient . . . : 9 . 739 increm: 0 . 10 ft NOTCH WEIR ID No. 305 Description: emergency overflow cb Weir Length: 4 . 7100 ft . Weir height (p) : 4 . 0000 ft . Elevation : 395 . 10 ft . Weir Increm: 0 . 10 DISCHARGE LIST ID No . 31 Description: FROM DEPRESSION 31, EAST COMBINATION DISCHARGE ID No. 310 Description: Structure: 300 Structure : 301 Structure : 303 Structure : Structure: 305 DISCHARGE LIST ID No. 40 Description: FROM DEPRESSION 40, EAST COMBINATION DISCHARGE ID No. 400 Description: Structure: 401 Structure : Structure : 402 Structure: Structure : 403 4/ 4/94 Dodds Engineers, Incorporated page 4 THE ORCHARDS -- 88008 DRAINAGE ANALYSIS DISCHARGE STRUCTURE LIST MULTIPLE ORIFICE ID No . 401 Description: Outlet Elev: 396. 00 Elev: 394 . 00 ft Orifice Diameter: 8 . 0000 in. NOTCH WEIR ID No . 402 Description: Weir Length: 3 . 1400 ft . Weir height (p) : 2 .5000 ft . Elevation : 398 . 60 ft . Weir Increm: 0 . 10 RISER DISCHARGE ID No. 403 Description: Riser Diameter (in) : 18 . 00 elev: 398 . 00 ft Weir Coefficient . . . : 3 . 782 height : 399. 00 ft Orif Coefficient . . . : 9 . 739 increm: 0 . 10 ft DISCHARGE LIST ID No. 50 Description: FROM DEPRESSION 50, EAST s . Mil WL f 10%31 ■ �'�� - �- mow. YA PAMCIc_ ►� I IN pampa, I I •I I ' ', , i1 • • • I'VO.7!^`ter M;VON mill KA • Min � ► MIR 'all )1, ��► F MAN mow- i MIN . - ILI ��,, lid. ,� ►�� Iwo ►/i r KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS INKING COUNTY HYDROLOGIC HYDROLOGIC SOIL GROUP GROUP* SOIL GROUP GROUP` Alderwood C Orr-as Peat D Arents, Alderwood Material C Oridia D Arents, Everett Material B Ovall C Beausite C Pilchuck C Bellingham D Puget D Briscot D Puyallup B Buckley D Ragnar B Coastal Beaches Variable Renton D Earlmont Silt Loam D Riverwash Variable Edgewick C Salal C Everett A Sammamish D Indianola A Seattle D Kitsap C Shacar D Klaus C Si Silt C Mixed Alluvial Land Variable Snohomish D Neilton A Sultan C Newberg B Tukwila D Nooksack C Urban Variable Normal Sandy Loam D Woodinville D HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting chiefly of deep, well-to-excessively drained sands or gravels. These soils have a high rate of water transmission. B. (Moderately low runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. C. (Moderately high runoff potential). Soils having slow Infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a hardpan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. • From SCS, TR-55, Second Edition,June 1986, Exhibit A-1. Revisions made from SCS, Soil Interpretation Record, Form #5, September 1988. 3.5.2-2 I/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TABLE 3.5.2B SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D Cultivated land(1): winter condition 86 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: 65 78 85 89 Wood or forest land: undisturbed 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 Open spaces, lawns, parks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 86 90 fair condition: grass cover on 50% to 75% of the area 77 85 90 92 Gravel roads and parking lots 76 85 89 91 Dirt roads and parking lots 72 82 87 89 Impervious surfaces, pavement, roofs, etc. 98 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 Single Family Residential (2) Dwelling Unit/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA 54 7.0 DU/GA 56 Planned unit developments, % impervious condominiums, apartments, must be computed commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 3.5.2-3 1/90 4(1 cj all N •. [ 11• In• Ili'i.'1T. 419 l Tj II 1 O 93 In to 461 •.1 � 1 1 '1� � II � - 1� ❑ Cl LJ 11 1I 4423 O arm as —ram FOM1 ■ut n' ,W I l/ 490 7. :I ,1I ,'llpKttot,t ,tLt+l'•itlgoi �:, 'I.:'� .�,�• ) '' -�/� s:�1 19t - --- Flo'• _ a,. ► M ,':, T jai { I� JNI17 401 to. On 411 CO 93 63 U. LJ I J I r M IT •, Ej 11 I 1, t'1••, I • . . .', \•�!•,.'''• ,1' •jr, •1 '+,.. ' O ,` 'I sit IL ,,• w . •, to `r i`!:�;2.7 .i �:• 'i. :i 0-I I I (' �!jf17fJTt//M► /►I• 11 t!,/•. .,L�t+, , '`' • C-�� If it . � .nlrfN, � ;1_.,-- ern_ 1.I `•,t,::;► � ' .t �..t. ' ••.I.c,.i:,l;� �t,� L -•'� 1 t I.l ,'1 • II� /'� ��'1 ''! i.l<111�':t j��:.'„I'. ;i. V I I --al V �'_, �: :I�''. I:'aJ .r�IJ�•Ir ll,j',il l.l� n_•.�) ,' emu•N •, lx, it r' r. 1.1:. 1'r• 1 ,� lJ ;� ', 1� 11 - :Z ,o• �n x.l, i ' I ,, t, •1.'��;I' I , _�^ co 4 10 p .o• x ••v 11�� �1�� nl j• .1 0 '1 t 1 i -r! I •� °D --�' ---lI.f1r• es -=_t 1= y >Itt---- o --- - -- -��'= - ro.t Z $A- I p 4 -Ir 7- 1 - - _ - -- _ t MIC m �� 1'"•1' i'Ir�.,r:t.. C!,' 1, j '•r�1.rl);�,,'�LI" 'i..l'. U .._I ! M " ty'.�../yvl+•.,�'1•.�•.�.ia7-,:,ify I�f'I.•':11�.�1�,��,t/.' .!:' '�7•.: ;t,�. . ( cu 't .ti j'..,r�•: .;�, /: :'i.• � •.•t:•..,,I•�,•• !.�.:t� ,'(;•li)�hl•I,o11.f. '.,_)• h . ' 'r i•, , • ...•��, :-r •1',:Y'•• '. i;�;i •'1'I' r;r';. •'. � • u,•►/,•� ��+:r ..'• ti 1 • • .. • 1 � /:''``•ia:.l•.�:,•�,')',1�,,1�1''I, 1'.,ry'�r 11�,.1 4�I.II,��I IM(l ) ., ,1 .r 1,",.I' 1. . D � '1 y_;' 7�!,:.'. .``'I r;l ,. : .!.S '�1:'.,•� ':I•�;)r; 'f,r.. '�I�'JIl•�♦ :r�•II V, . 1 '^ •" •NI: .I�al1:'f'j:l��rl.+:rf;'•j'1i".:'.! •,'.:•' ,II. f',•;.(;'•�.'�.i:r,�l:�',�!!+r. + .�'I Iluls•nphnnin/p•nti ,f f'1'�' << , tr;•r'1'i,1' �,ik•I�11( 1 r.`,.,�1�•. '��,11�7 'r :I - '�, � /A � I�iorllbn/o/SKt• �tl��•� 1N .•. �'t'��i ( i /q^Z• J 1 h 1. W �ii'.t.^• t.:..ra....l.lw. r,( I. ! t :.. a/+.1.••... i.'r:/�� .� '', •�' '�.tbhyol•r prW L•1•d b1�•li,biil fro�1'+loif �I�Rr1iI Nis Ing"!1"M 16n• Date of Session:12/12/91 REM ** INCLUDES OFFSITE BYPASS FOR PEAK FLOW ROUTING ** REM ** 1/2 2YR,2YR ** LSTEND ZERO 520 MOVE OW-A2 to 10 ADD Z-A 10 10 LPOOL 1"DEV WEST 2YR"1 10 100 110 5 REM ** 2YR,IOYR ** LSTEND MOVE OW-A to 11 ADD Z-B 11 11 LPOOL 2"DEV WEST IOYR"2 11 100 110 6 REM ** 100 YR ** LSTEND MOVE OW-C to 12 ADD Z-C 12 12 LPOOL 3"DEV WEST 100YR"3 12 100 110 7 REM ** IOOYR,7DAY ** LSTEND MOVE OW-D to 13 ADD Z-D 13 13 LPOOL 4"DEV WEST 100YR,7DAY"4 13 100 110 8 Date of Session:4/4/94 ZERO 120 REM ** 1/2 2YR,2YR ** LSTEND MOVE A2-Ato 6 ADD OW-A 6 6 LPOOL 1"2YR EX,WEST"6 6 10 10 7 ADD AI-AJ-A 1 ADD 17 1 ADD 21 2 DIVERT 50.0 120 PERCENT ZERO 520 REM ** EX 100 YR '* LSTEND MOVE A2-C to 6 ADD OW-C 6 6 LPOOL 2"EX WEST 100YR"6 6 10 10 7 ADD AI-C 7 3 ADD J-C 3 3 REM ** EX 100YR,7DAY ** LSTEND MOVE A2-Dto 6 ADD OW-D 6 6 LPOOL 3"EX WEST 100YR,7DAY"6 6 10 10 7 ADD AI-D 7 4 ADD J-D 4 4 Date of Session: 12/13/91 ADD 01-A 8 8 REM **EX 1/2 2YR** ADD 87 8 LSTEND LPOOL 3"EAST"8 8 40 40 9 ZERO 120 ADD B-A 10 10 MOVE E-A2 to 6 ADD 02-A 10 10 LPOOL 2"EAST"6 6 50 50 7 LPOOL 4"EAST"10 10 3131 11 ADD F-A2 8 8 MOVE C-A to 12 ADD O1-A2 8 8 MOVE D-A to 14 ADD 8 7 8 ADD 11 12 12 LPOOL 3"EAST"8 8 40 40 9 LPOOL 5"EAST"12 12 30 30 13 ADD B-A21010 ADD 13 14 14 ADD 02-A21010 ADD 9 14 14 LPOOL 4"EAST"10 10 3131 11 LPOOL 6"EAST"14 14 20 20 15 MOVE C-A2 to 12 ADD G-A 15 16 MOVE D-A2 to 14 ADD 03-A 16 16 ADD 11 12 12 ADD I-A 16 17 LPOOL 5'BAST"12 12 30 30 13 ADD 05-A 17 17 ADD 13 14 14 ADD 04-A 17 17 ADD 9 14 14 ADD H-A 17 18 LPOOL 6'BAST"14 14 20 20 15 ADD 06-A 18 18 ADD G-A21616 ADD 182 2 ADD 03-A21616 REM **EX 100 YR s* ADD 15 16 16 LSTEND ADD I-A21717 ZERO 5 20 ADD 05-A21717 MOVE E-C to 6 ADD 04-A21717 LPOOL 2'BAST"6 6 50 50 7 ADD 16 17 17 ADD F-C 8 8 ADD H-A21818 ADD 01-C 8 8 ADD 06-A21818 ADD 87 8 ADD 1817 1 LPOOL 3'BAST"8 8 40 40 9 REM ** 2YR s* ADD B-C 10 10 LSTEND ADD 02-C 10 10 ZERO 6 20 LPOOL 4"EAST"10 10 3131 11 MOVE E-A to 6 MOVE C-C to 12 LPOOL 2"EAST"6 6 50 50 7 MOVE D-C to 14 ADD F-A 8 8 ADD 11 12 12 LPOOL 5"EAST"12 12 30 30 13 ADD 13 14 14 ADD 9 14 14 ADD 15 16 16 LPOOL 6"EAST"14 14 20 20 15 ADD I-D 17 17 ADD G-C 16 16 ADD 05-D 17 17 ADD O3-C 16 16 ADD 04-D 17 17 ADD 151616 ADD 161717 ADD 1-C 17 17 ADD H-D 18 18 ADD O5-C 17 17 ADD 06-D 18 18 ADD 04-C 17 17 ADD 1718 4 ADD 16 17 17 ADD H-C 18 18 ADD 06-C 18 18 ADD 17 18 3 REM "100 YR,7 DAY" LSTEND ZERO 5 20 MOVE E-D to 6 LPOOL 2"EAST"6 6 50 50 7 ADD F-D 8 8 ADD 01-D 8 8 ADD 87 8 LPOOL 3"EAST'8 8 40 40 9 ADD B-D 10 10 ADD 02-D 10 10 LPOOL 4"BAST"10 10 3131 11 MOVE C-D to 12 MOVE D-D to 14 ADD 11 12 12 LPOOL 5"EAST'12 12 30 30 13 ADD 13 14 14 ADD 9 14 14 LPOOL 6"EAST'14 14 20 20 15 ADD G-D 1616 ADD 03-D 16 16 Date of Session: 1/3/91 DEV.ROUTING-88008-THE ORCHARDS REM '*OFFSITE BYPASS INCLUDED IN PEAK FLOW ROUTING ** REM '*1/2 2YR,2YR** REM '*100YR'* LSTEND LSTEND ZERO 520 ZERO 17 20 ADD 01-A2 17 17 MOVE 01-C to 17 ADD 02-A2 17 17 ADD 02-C 1717 ADD X-A 17 17 ADD X-C 1717 LPOOL 1"POND#1,2YR"1 17 200 210 18 LPOOL 6"POND#1,100YR"3 17 200 210 18 ADD W-A 18 18 ADD W-C 18 18 LPOOL 2'POND#3,2YR"1 18 400 400 19 LPOOL 6"POND#3,100YR"1 18 400 400 19 ADD 03-A2 13 13 ADD 06-C 15 15 ADD 04-A2 13 13 ADD 03-C 15 15 ADD 06-A2 13 13 ADD 04-C 15 15 ADD 05-A2 19 20 ADD O5-C 19 20 ADD V-A 20 20 ADD V-C 20 20 ADD Y-A 20 20 ADD Y-C 20 20 LPOOL 3'POND#2,2YR"120 300 310 9 LPOOL 7"POND#2,100YR"3 20 300 310 11 ADD 13 9 5 ADD 15 11 7 REM **2YR,IOYR'* REM **100YR,7 DAY** LSTEND LSTEND ZERO 1720 ZERO 17 20 MOVE 01-A to 17 ADD 01-D 1717 ADD 02-A 17 17 ADD 02-D 17 17 ADD X-B 1717 ADD X-D 1717 LPOOL 4"POND#1,IOYR"2 17 200 210 18 LPOOL 8"POND#1,100YR-7D"4 17 200 210 18 ADD W-B 18 18 ADD W-D 18 18 LPOOL 4'POND#3,IOYR"1 18 400 400 19 LPOOL 9'POND#3,100YR-7DAY"1 18 400 400 19 ADD 03-A 14 14 ADD 06-D 16 16 ADD 04-A 14 14 ADD 03-D 16 16 ADD 06-A 14 14 ADD 04-D 16 16 ADD 05-A 19 20 ADD 05-D 19 20 ADD V-B 20 20 ADD V-D 20 20 ADD Y-B 20 20 ADD Y-D 20 20 LPOOL 5'POND#2,10YR"2 20 300 310 10 LPOOL 10"POND#2,100YR-7D"4 20 300 310 12 ADD 14 10 6 ADD 16 12 8 ZERO 17 20 F. BIOFILTRATION DESIGN CALCULATIONS 1 C1 `TR t I ' 1�L BU R` WATER BUILDINGS, STREETS, TOTAL TOTAL 2-YEAR 200' SWALE SURFACE DESIGN DESIGN TOTAL SIDEWALKS, DRIVEWAYS, IMPERVIOUS PERVIOUS PERVIOUS PEAK FLOW WIDTH AREA SWALE SWALE SUB-BASIN AREA &GARAGES &PARKING AREA AREA CN RATE REQUIRED REQUIRED LENGTH WIDTH A 4.19 AC 1.27 AC 0.73 AC 2.00 AC 2.19 AC 86 1.11 CFS 2.75 FT 1350 SQ FT 130 FT 6.4 FT B 2.87 0.74 0.84 1.58 1.29 86 0.81 1.7 1140 130 4.8 C 4.48 1.46 0.88 2.34 2.14 86 1.23 3.2 1440 125 7.5 D 2.27 0.33 0.97 1.30 0.97 86 1.17 3.0 1400 110 8.7 E 3.01 0.99 0.52 1.51 1.50 86 0.81 1.7 1140 120 5.5 F 2.96 0.72 0.99 1.72 1.24 86 0.86 2.0 1200 100 8.0 G 9.32 2.75 2.27 5.02 4.30 86 SEE WETPOND ANALYSIS, SECTION G. H 0.94 0.09 0.42 0.51 0.43 86 0.26 0.0 700 100 3.0 I 1.00 0.11 0.18 0.29 0.71 86 0.22 0.0 660 150 1.0 J 2.56 0.50 0.91 1.41 1.15 86 1.89 5.5 1900 135 10.1 K 2.17 0.48 0.92 1.40 0.77 86 0.66 1.1 1020 100 6.2 L 3.13 0.79 0.98 1.77 1.36 86 1.55 4.3 1660 150 7.1 M 2.30 0.43 0.63 1.06 1.24 86 0.60 1.0 1000 120 4.3 N 2.01 0.42 0.85 1.27 0.74 86 0.61 1.0 1000 130 3.7 O 2.38 0.28 0.82 1.10 1.28 85.1 0.62 1.0 1000 120 4.3 P 1.00 0.23 0.46 0.69 0.31 86 0.32 0.0 760 125 2.1 Q 1.10 0.30 0.44 0.74 0.36 86 0.34 0.0 800 100 4.0 3/20/92 Dodds Engineers , Incorporated page 1 THE ORCHARDS -- 88008 BIOFILTRATION SWALE ANALYSIS 3/19/92 BY: GRS --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN RESULT SUMMARY BASIN -----VOLUME---- -RATE- ----TIME----- Hydrograph Area 1D ---cf-- Ac-ft --cfs- -ain- hours Methodology Acres ------------------------------------------------------------------------- ------------------------------------------------------------------------- A2 19631 0.45 1.11 480 8.00 SBUH Method 4.19 B2 14152 0.32 0.81 480 8.00 SBUH Method 2.87 C2 21667 0.50 1.23 480 8.00 SBUH Method 4.48 D2 11363 0.26 0.65 480 8.00 SBUH Method 2.27 E2 14349 0.33 0.81 480 8.00 SBUH Method 3.01 F2 14900 0.34 0.86 480 8.00 SBUH Method 2.96 G-3 9596 0.22 0.52 480 8.00 SBUH Method 9.32 G2 45585 1.05 2.60 480 8.00 SBUH Method 9.32 H2 4610 0.11 0.26 480 8.00 SBUH Method 0.94 I2 4056 0.09 0.22 480 8.00 SBUH Method 1.00 32 12626 0.29 0.72 480 8.00 SBUH Method 2.56 K2 11390 0.26 0.66 480 8.00 SBUH Method 2.17 L2 15592 0.36 0.89 480 8.00 SBUH Method 3.13 M2 10649 0.24 0.60 480 8.00 SBUH Method 2.30 N2 10461 0.24 0.61 480 8.00 SBUH Method 2.01 02 11030 0.25 0.62 480 8.00 SBUH Method 2.38 P2 5400 0.12 0.32 480 8.00 SBUH Method 1.00 Q2 5876 0.13 0.34 480 8.00 SBUH Method 1.10 ® � D D O D S E N G I N E E R S, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G RLANNING DAT E 4205 146TH AVE. N.E., SUITE 200 - BELLEVUE. WA 96007 [206] B65-7677 OR 454-3743 B Y BASIN SUMMARY BASIN ID: A2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4.19 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 2.19 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 2.00 Acres CN. . . . . 98.00 PEAK RATE: 1.11 cfs VOL: 0.45 Ac-ft TIME: 480 min BASIN ID: E2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3.01 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 1.50 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.51 Acres CN. . . . . 98.00 PEAK RATE: 0.81 cfs VOL: 0.33 Ac-ft TIME: 480 min c) �cS _- - ,... OD SWALE A :,.. , �.. ; .i t a o SWALE E ' 5\NII LE A ' L= )50' NDTH= (,A' Qz= 1 1 CF5 SLOPE= S1Nr3LE E: L= IZO' WI0T>4= 5,5' Qz= 0-b CFS 4 L(_ SIN M t-E�S TO bE VEG ETA7"EO w J-T n W L 7 L r°,- 0- 7YXE C�er�-?SSG, SHEET OF D D D D S ENGINEERS, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G R L A N N I N G DAT E 4205 146TH AVE. N.E.• SUITE 200 - BELLEVUE. WA 98007 (206] 8135-7677 OR 454-3743 B Y BASIN ID: B2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.87 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 1.29 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.58 Acres CN. . . . : 98.00 PEAK RATE: 0.81 cfs VOL: 0.32 Ac-ft TIME: 480 min BASIN ID: C2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4.48 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 2.14 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 2.34 Acres CN. . . . : 98.00 PEAK RATE: 1.23 cfs VOL: 0.50 Ac-ft TIME: 480 min 1 ran' yj C) CFS ` y y' I Z5 WILL 13E LENG7u�N�0 O1 I o �� SHEET OF ®ice D D O D S ENGINEERS, INC. ,JOB NO. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G [--)AT E 4205 148TH AVE. N.E., SUITE 200 - BELLEVUE, WA 96007 [206) BB5-7877 OR 454-3743 S Y BASIN ID: D2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.27 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.97 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.30 Acres CN. . . . : 98.00 PEAK RATE: 0.65 cfs VOL: 0.26 Ac-ft TIME: 480 min BASIN ID: J2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.56 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 1.15 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.41 Acres CN. . . .: 98.00 PEAK RATE: 0.72 cfs VOL: 0.29 Ac-ft TIME: 480 min FF i ALE DI 4 399.0 WALE J I I i CKE 396 400 - - - - -- - - - - IN I SN(4L.E D; L:= i Io' 1NID7 4: 8,-7' SL,oPe QZ= )1)7 CFS ( IMCI,vOER-�) FLOyk!5 +FVEV!U;1'�SL i 7 iZyf3i=Q ;Y SMLE F sw►�t.E � L-- 135 v)I D'T I'= i0,1 DUPE= 05/0 Q7-= )'59 Cps (1Nc��oES �!�w5 PR��/.OVsL� 7e�A 7 co 5Y sw D� N07E; Focz SEr2f=5- �YJ WJ,-J i rj5 �k117H+ 10-jOL 001- (, � 4EO FLOWS, 70 MEE7 B10;7�= SHEET OF ®jam DODOS ENGINEERS, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G DAT E 4205 146TH AVE. N.E.. SUITE 200 - BELLEVUE, WA 96007 BY (2061 BB5-7677 OR 454-3743 BASIN ID: F2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.96 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 1.24 Acres TIME INTERVAL. . . . : 10.00 min CN. . . .: 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.72 Acres CN. . . . . 98.00 PEAK RATE: 0.86 cfs VOL: 0.34 Ac-ft TIME: 480 min 4V7 SvJ(�LC F, i �o L= 'vU� j� 404 wis 0 -71 9� Af ,6 � // r VO• r.! SHEET OF �i- O O D O S ENGINEERS, INC. ,JOB NO. CIVIL ENGINEERING SURVEYING PLANNING DATE 4205 146TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 (2061 B135-7677 OR 454-3743 E1 Y BASIN ID: H2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0.94 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.43 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 2.0.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 0.51 Acres CN.. . . : 98.00 PEAK RATE: 0.26 cfs VOL: 0.11 Ac-ft TIME: 480 min 't , L S_ 4 00- SVgHLC h 398 SWALE H UPC= aZ� O,3 Cf--S .; �a:• x x c k Y. F F O� SHEET OF DDDDS ENGINEERS, INC. JOB NO. CIVIL E NGIN E ERING S U R V E Y I N G R L A N N I N G OAT E 4205 146TH AVE. N.E., SUITE 200 - BELLEVUE. WA 96007 [2061 BB5-7B77 OR 454-3743 B Y BASIN ID: I2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1.00 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.71 Acres TIME INTERVAL. . . . ; 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 0.29 Acres CN. . . . : 98.00 PEAK RATE: 0.22 cfs VOL: 0.09 Ac-ft TIME: 480 min I r I SLUPE = 0.5% FF 400.5 WALE I I O 4 N 398- 11 SHEET OF �i- DODDS ENGINEERS, INC. JOB NO. CIVIL ENGINEERING SURVEYING PLANNING DATE 4205 146TH AVE. N.E.. SUITE 200 - BELLEVUE, WA 98007 [2061 965-7677 OR 454-3743 B Y Q z: BASIN ID: K2 NAME: i SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.17 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.77 Acres l TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 j TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.40 Acres 0 I aD CN. . . . : 98.00 PEAK RATE: 0.66 cfs VOL: 0.26 Ac-ft TIME: 480 min I BASIN ID: L2 NAME: 0 SBUH METHODOLOGY ALE K TOTAL AREA. . . . . . . : 3.13 Acres BASEFLOWS: 0.00 cfs J � RAINFALL TYPE. . . . : USER1 PERVIOUS AREA t � I PRECIPITATION. . . . : 2.00 inches AREA. . : 1.36 Acres (� TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA f ABSTRACTION COEFF: 0.20 AREA. . : 1.77 Acres CN. . . . : 98.00 PEAK RATE: 0.89 cfs VOL: 0.36 Ac-ft TIME: 480 min BASIN ID: M2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.30 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 1.24 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA a t ABSTRACTION COEFF: 0.20 AREA. . : 1.06 Acres CN. . . . . 98.00 PEAK RATE: 0.60 cfs VOL: 0.24 Ac-ft TIME: 480 min w Co L= 100 WIDTH.:: &,Z' SLOPE= O.S% i 0,7 cFS SwALe L I L= 150) w1107 H= 7,I' 3(.OP67= (D,-5o/!) r T SWALE L i o JAI "7- L= IZCU� WIDTH.;: 4,3 5LUPE= O:-j?o E I I y S6. � I WALE SHEET OF DODDS ENGINEERS, INC. JOB NO. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G OAT E 4205 14BTH AVE. N.E., SUITE 200 - BELLEVUE, WA 96007 1206) 665-7B77 OR 454-3743 B Y BASIN ID: N2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.01 Acres BASEFLOWS: 0.00 cfs Sr o� t•Y RAINFALL TYPE. . . . : USER1 PERVIOUS AREA , NY 4 PRECIPITATION. . . . : 2.00 inches AREA. . : 0.74 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 1.27 Acres CN. . . . : 98.00 PEAK RATE: 0.61 cfs VOL: 0.24 Ac-ft TIME: 480 min ti /�'.'• 1 � BASIN ID: 02 NAME: k SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2.38 Acres BASEFLOWS: 0.00 cfs " RAINFALL TYPE. . . . : USER1 PERVIOUS AREA " 398 PRECIPITATION. .. . : 2.00 inches AREA. . : 1.28 Acres * ., X r......•.•. j ,• TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA X rKYY,*Y*k XX Y KY . ::. j ABSTRACTION COEFF: 0.20 AREA. . : 1.10 Acres CN. . . . : 98.00 t'•: PEAK RATE: 0.62 cfs VOL: 0.25 Ac-ft TIME: 480 min A X Y( swAr_E N L= 130� W D i H 3 3,-7' �.,:• . �: I Q - O�(� CFI L_ �4 SWALE N r lr= I CU' o)o 1 H= X. g 9, SHEET OF DODDS ENGINEERS, INC. JOB NO. CIVIL ENGINEERING SURVEYING PLANNING DATE 4205 148TH AVE. N.E.. SUITE 200 - BELLEVUE, WA 98007 [206) 865-7877 OR 454-3743 B Y BASIN ID: P2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1.00 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.31 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 0.69 Acres CN. . . . . 98.00 PEAK RATE: 0.32 cfs VOL: 0.12 Ac-ft TIME: 480 min BASIN ID: Q2 NAME: SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1.10 Acres BASEFLOWS: 0.00 cfs RAINFALL TYPE. . . . : USER1 PERVIOUS AREA PRECIPITATION. . . . : 2.00 inches AREA. . : 0.36 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 86.00 TIME OF CONC. . . . . : 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF: 0.20 AREA. . : 0.71 Acres CN. . . . . 98.00 PEAK RATE: 0.34 cfs VOL: 0.13 Ac-ft TIME: 480 min 408 7 408 — 408 406 - FFj SWAL P \ L= 1Z5 I Y�ia��= Z,1 51-oPE_ 0,5% Qz= 0,3 CFS SV�I HLG Q L= I vU' Vq l D7N= 4,o' -�Lvps Qz- 03 CF5 SHEET OF DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 0.00 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)- 3.00 OPERATOR: BOTTOM SLOPE(FTIFT)= 0.0200 DATE: MANNING'S n 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.0075 0.3162 0.0237 0.000 0.050 0.10 0.0300 0.6325 0.0474 0.002 0.079 0.15 0.0675 0.9487 0.0712 0.007 0.103 0.20 0.1200 1.2649 0.0949 0.015 0.125 0.25 0.1875 1.5811 0.1186 0.027 0.145 0.30 0.2700 1.8974 0.1423 0.044 0.164 0.35 0.3675 2.2136 0.1660 1 0.067 0.181 0.40 0.4800 2.5298 0.1897 0.095 0.198 0.45 0.6075 2.8460 0.2135 0.130 0.214 0.50 0.7500 3.1623 0.2372 0.173 0.230 0.55 0.9075 3.4785 0.2609 0.222 0.245 0.60 1.0800 3.7947 0.2846 0.281 0.260 0.65 1.2675 4.1110 1 0.3083 0.347 0.274 0.70 1.4700 4.4272 0.3320 1 0.423 0.288 0.75 1.6875 4.7434 0.3558 0.509 0.301 0.80 1.9200 5.0596 0.3795 0.604 0.315 0.85 2.1675 5.3759 0.4032 0.710 0.328 0.90 2.4300 5.6921MO..641646 0.827 0.340 0.95 2.7075 6.0083 0.956 0.353 1.00 3.0000 6.3246 1.096 0.365 1.10 3.6300 6.9570 1.413 0.389 1.20 4.3200 7.5895 1.782 0.412 1.30 5.0700 8.2219 2.205 0.435 1.40 5.8800 8.8544 0.6641 2.687 0.457 1.50 6.7500 9.4868 0.7115 3.230 0.479 1.60 7.6800 10.1193 0.7589 3.837 0.500 1.70 8.6700 10.7517 0.8064 4.510 0.520 1.80 9.7200 11.3842 0.8538 5.253 1 0.540 1.90 10.8300 12.0167 0.9012 6.067 0.560 2.00 12.0000 12.6491 0.9487 6.957 0.580 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 0.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FTIFT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.0325 0.8162 0.0398 0.002 0.070 0.10 0.0800 1.1325 0.0706 0.008 0.103 0.15 0.1425 1.4487 0.0984 0.018 0.128 0.20 0.2200 1.7649 0.1247 0.033 0.150 0.25 0.3125 2.0811 0.1502 0.053 0.170 0.30 0.4200 2.3974 0.1752 0.079 0.188 0.35 0.5425 2.7136 0.1999 0.111 0.205 0.40 0.6800 3.0298 0.2244 0.151 0.222 0.45 0.8325 3.3460 0.2488 0.198 0.238 0.50 1.0000 3.6623 0.2731 0.253 0.253 0.55 1.1825 3.9785 0.2972 0.316 0.267 0.60 1.3800 4.2947 0.3213 0.389 0.282 0.65 1.5925 4.6110 0.3454 0.471 0.296 0.70 1.8200 4.9272 0.3694 0.563 0.309 0.75 2.0625 5.2434 0.3934 0.665 0.322 0.80 2.3200 5.5596 0.4173 0,778 0.335 0.85 2.5925 5.8759 0.4412 0.902 0.348 0.90 2.8800 6.1921 0.4651 1 1.038 0.360 0.95 3.1825 6.5083 0.4890 1.186 0.373 1.00 3.5000 6.8246 0.5129 1.346 0.385 1.10 4.1800 7.4570 0.5605 1.706 0.408 1.20 4.9200 8.0895 0.6082 2.121 0.431 1.30 5.7200 8.7219 0.6558 2.592 0.453 1.40 6.5800 9.3544 0.7034 3.125 0.475 1.50 7.5000 9.9868 0.7510 3.721 0.496 1.60 8.4800 10.6193 0.7985 4.383 0.517 1.70 9.5200 11.2517 0.8461 5.113 0.537 1.80 10.6200 11.8842 0.8936 5.916 0.557 1.90 11.7800 12.5167 0.9411 6.793 0.577 2.00 13.0000 1 13.1491 1 0.9887 1 7.747 0.596 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FI)= 1.00 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FT/FT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.0575 1.3162 0.0437 0.004 0.074 0.10 0.1300 1.6325 0.0796 0.014 0.111 0.15 0.2175 1.9487 0.1116 0.030 0.139 0.20 0.3200 2.2649 0.1413 0.052 0.163 0.25 0.4375 2.5811 0.1695 0.080 0.184 0.30 0.5700 2.8974 0.1967 0.116 0.203 0.35 0.7175 3.2136 0.2233 0.159 0.221 0.40 0.8800 3.5298 0.2493 0.209 0.238 0.45 1.0575 3.8460 0.2750 0.268 0.254 0.50 1.2500 4.1623 0.3003 0.337 0.269 0.55 1.4575 4.4785 0.3254 0.414 0.284 0.60 1.6800 4.7947 0.3504 0.501 0.298 0.65 1.9175 5.1110 1 0.3752 0.599 0.312 0.70 2.1700 5.4272 0.3998 0.707 0.326 0.75 2.4375 5.7434 0.4244 0.827 0.339 0.80 2.7200 6.0596 0.4489 0.957 0.352 0.85 3.0175 6.3759 0.4733 1.100 0.365 0.90 1 3.3300 6.6921 0.4976 1.256 0.377 0.95 3.6575 7.0083 0.5219 1.424 0.389 1.00 4.0000 7.3246 0.5461 1.605 0.401 1.10 4.7300 7.9570 0.5944 2.008 0.424 1.20 5.5200 8.5895 0.6426 2.468 0.447 1.30 6.3700 9.2219 0.6907 2.989 0.469 1.40 7.2800 9.8544 0.7388 3.572 0.491 1.50 8.2500 10.4868 0.7867 4.221 0.512 1.60 9.2800 11.1193 0.8346 4.939 0.532 1.70 10.3700 11.7517 0.8824 5.728 0.552 1.80 11.5200 12.3842 0.9302 6.591 0.572 1.90 12.7300 1 13.0167 0.9780 1 7.531 1 0.592 2.00 14.0000 13.6491 1.0257 8.550 0.611 20-Mar-92 DODDS ENGINEERS, INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 1.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FTIFT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.0825 1.8162 0.0454 0.006 0.076 0.10 0.1800 2.1325 0.0844 0.021 0.116 0.15 0.2925 2.4487 0.1195 0.043 0.146 0.20 0.4200 2.7649 0.1519 0.072 0.171 0.25 0.5625 3.0811 0.1826 0.109 0.193 0.30 0.7200 3.3974 0.2119 0.154 0.213 0.35 0.8925 3.7136 0.2403 0.207 0.232 0.40 1.0800 4.0298 0.2680 0.270 0.250 0.45 1.2825 4.3460 0.2951 0.341 0.266 0.50 1.5000 4.6623 0.3217 0.423 0.282 0.55 1.7325 4.9785 0.3480 0.515 0.297 0.60 1.9800 5.2947 0.3740 0.617 0.312 0.65 2.2425 5.6110 0.3997 0.731 0.326 0.70 2.5200 5.9272 0.4252 0.856 0.339 0.75 2.8125 6.2434 0.4505 0.992 0.353 0.80 3.1200 6.5596 0.4756 1.141 0.366 0.85 3.4425 6.8759 0.5007 1.303 0.379 0.90 3.7800 7.1921 0.5256 1.478 0.391 0.95 4.1325 7.5083 0.5504 1 1.666 0.403 1.00 4.5000 7.8246 0.5751 1.869 0.415 1.10 5.2800 8.4570 0.6243 2.316 0.439 1.20 6.1200 9.0895 0.6733 2.823 0.461 1.30 7.0200 9.7219 0.7221 3.393 0.483 1.40 7.9800 10.3544 0.7707 4.028 0.505 1.50 9.0000 10.9868 0.8192 4.731 0.526 1.60 10.0800 11.6193 0.8675 5.505 0.546 1.70 11.2200 12.2517 0.9158 6.353 0.566 1.80 12.4200 12.8842 0.9640 7.277 1 0.586 1.90 13.6800 1 13.5167 1.0121 8.280 0.605 2.00 15.0000 14.1491 1.0601 9.364 0.624 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 2.00 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB,#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FI'/F�= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.1075 2.3162 0.0464 0.008 0.078 0.10 0.2300 2.6325 0.0874 0.027 0.118 0.15 0.3675 2.9487 0.1246 0.055 0.150 0.20 0.5200 3.2649 0.1593 0.092 0.176 0.25 0.6875 3.5811 0.1920 0.137 0.200 0.30 0.8700 3.8974 0.2232 0.192 0.221 0.35 1.0675 4.2136 0.2533 0.257 0.240 0.40 1.2800 4.5298 0.2826 0.331 0.259 0.45 1.5075 4.8460 0.3111 0.416 0.276 0.50 1.7500 5.1623 0.3390 0.511 0.292 0.55 2.0075 5.4785 0.3664 0.617 0.307 0.60 2.2800 5.7947 0.3935 0.735 0.322 0.65 2.5675 6.1110 0.4201 0.865 0.337 0.70 2.8700 6.4272 0.4465 1.007 0.351 0.75 3.1875 6.7434 0.4727 1.161 0.364 0.80 3.5200 7.0596 0.4986 1.329 0.378 0.85 3.8675 7.3759 0.5243 1.510 0.390 0.90 4.2300 7.6921 0.5499 1.705 0.403 0.95 4.6075 8.0083 0.5753 1.914 0.415 1.00 5.0000 8.3246 0.6006 2.137 0.427 1.10 5.8300 8.9570 0.6509 2.629 0.451 1.20 6.7200 9.5895 1 0.7008 3.183 1 0.474 1.30 7.6700 10.2219 0.7503 3.803 0.496 1.40 8.6800 10.8544 0.7997 4.490 0.517 1.50 9.7500 11.4868 0.8488 5.248 0.538 1.60 10.8800 12.1193 0.8977 6.079 0.559 1.70 12.0700 12.7517 0.9465 6.987 0.579 1.80 13.3200 1 13.3842 0.9952 7.972 0.599 1.90 14.6300 14.0167 1.0438 9.039 0.618 2.00 16.0000 14.6491 1.0922 10.189 0.637 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(F )= 2.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FTIFT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.1325 2.8162 0.0470 0.010 0.078 0.10 0.2800 3.1325 0.0894 0.034 0.120 0.15 0.4425 3.4487 0.1283 0.068 0.153 0.20 0.6200 3.7649 0.1647 0.112 0.180 0.25 0.8125 4.0811 0.1991 0.166 0.205 0.30 1.0200 4.3974 0.2320 0.231 0.227 0.35 1.2425 4.7136 0.2636 0.307 0.247 0.40 1.4800 5.0298 0.2942 0.393 0.266 0.45 1.7325 5.3460 0.3241 0.491 0.283 0.50 2.0000 5.6623 0.3532 0.600 0.300 0.55 2.2825 5.9785 0.3818 0.721 0.316 0.60 2.5800 6.2947 0.4099 0.855 0.331 0.65 2.8925 6.6110 0.4375 1.001 0.346 0.70 3.2200 6.9272 0.4648 1.160 0.360 0.75 3.5625 7.2434 0.4918 1.333 0.374 0.80 3.9200 7.5596 0.5185 1.519 0.388 0.85 4.2925 7.8759 0.5450 1.720 0.401 0.90 4.6800 8.1921 0.5713 1.935 0.413 0.95 5.0825 8.5083 0.5974 2.165 0.426 1.00 5.5000 8.8246 0.6233 2.410 0.438 1.10 6.3800 9.4570 0.6746 2.947 0.462 1.20 7.3200 10.0895 0.7255 3.549 0.485 1.30 8.3200 10.7219 0.7760 4.218 0.507 1.40 9.3800 11.3544 0.8261 1 4.959 0.529 1.50 10.5000 11,9868 0.8760 5.772 0.550 1.60 11.6800 12.6193 0.9256 6.661 0.570 1.70 12.9200 13.2517 0.9750 7.628 0.590 1.80 14.2200 13.8842 1.0242 8.675 0.610 1.90 15.5800 14.5167 1.0732 9.806 0.629 2.00 17.0000 15.1491 1.1222 1 11.023 1 0.648 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 3.00 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FTIFT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.1575 3.3162 0.0475 0.012 0.079 0.10 0.3300 3.6325 0.0908 0.040 0.121 0.15 0.5175 3.9487 0.1311 0.080 0.155 0.20 0.7200 4.2649 0.1688 0.132 0.183 0.25 0.9375 4.5811 0.2046 0.195 0.209 0.30 1.1700 4.8974 0.2389 0.270 0.231 0.35 1.4175 5.2136 0.2719 0.357 0.252 0.40 1.6800 5.5298 0.3038 0.456 0.271 0.45 1.9575 5.8460 0.3348 0.567 0.290 0.50 2.2500 6.1623 0.3651 0.690 0.307 0.55 2.5575 6.4785 0.3948 0.826 0.323 0.60 2.8800 6.7947 0.4239 0.976 0.339 0.65 3.2175 7.1110 0.4525 1.139 0.354 0.70 3.5700 7.4272 0.4807 1.315 0.368 0.75 3.9375 7.7434 0.5085 1.506 0.383 0.80 4.3200 8.0596 0.5360 1.712 0.396 0.85 4.7175 8.3759 0.5632 1.932 0.409 0.90 5.1300 8.6921 0.5902 2.167 0.422 0.95 5.5575 9.0083 0.6169 2.418 0.435 1.00 6.0000 9.3246 0.6435 2.685 0.448 1.10 6.9300 9.9570 0.6960 3.268 0.472 1.20 7.9200 10.5895 0.7479 3.918 0.495 1.30 8.9700 11.2219 0.7993 4.639 0.517 1.40 10.0800 11.8544 0.8503 5.432 0.539 1.50 11.2500 12.4868 0.9009 6.301 0.560 1.60 12.4800 13.1193 0.9513 7.248 0.581 1.70 13.7700 13.7517 1.0013 8.275 0.601 1.80 1 15.1200 14.3842 1.0512 9.386 0.621 1.90 16.5300 15.0167 1.1008 10.581 0.640 2.00 18.0000 15.6491 1.1502 11.865 0.659 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 3.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.W JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FT/FT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.1825 3.8162 0.0478 0.014 0.079 0.10 0.3800 4.1325 0.0920 0.046 0.122 0.15 0.5925 4.4487 0.1332 0.093 0.157 0.20 0.8200 4.7649 0.1721 0.152 0.186 0.25 1.0625 5.0811 0.2091 0.225 0.212 0.30 1.3200 5.3974 0.2446 0.310 0.235 0.35 1.5925 5.7136 0.2787 0.408 0.256 0.40 1.8800 6.0298 0.3118 0.519 0.276 0.45 2.1825 6.3460 0.3439 0.643 0.295 0.50 2.5000 6.6623 0.3752 0.781 0.312 0.55 2.8325 6.9785 0.4059 0.932 0.329 0.60 3.1800 7.2947 0.4359 1.098 0.345 0.65 3.5425 7.6110 0.4654 1 1.277 0.361 0.70 3.9200 7.9272 0.4945 1.472 0.375 0.75 4.3125 8.2434 0.5231 1.681 0.390 0.80 4.7200 8.5596 0.5514 1.906 0.404 0.85 5.1425 8.8759 0.5794 2.146 0.417 0.90 5.5800 9.1921 0.6070 2.402 0.430 0.95 6.0325 9.5083 0.6344 2.674 0.443 1.00 6.5000 9.8246 0.6616 2.963 0.456 1.10 7.4800 10.4570 0.7153 3.592 0.480 1.20 8.5200 11.0895 0.7683 4.291 0.504 1.30 9.6200 11.7219 0.8207 5.063 0.526 1.40 10.7800 12.3544 0.8726 5.910 0.548 1.50 12.0000 12.9868 0.9240 6.835 0.570 1.60 13.2800 13.6193 0.9751 7.841 0.590 1.70 14.6200 14.2517 1.0258 8.929 0.611 1.80 16.0200 14.8842 1.0763 10.102 0.631 1.90 17.4800 15.5167 1.1265 11.363 0.650 2.00 19.0000 16.1491 1.17 55 12.714 0.669 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS 1310MLTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 4.00 JOB NAME: LEFT SIDE SLOPE(L.:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FT/FT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.2075 4.3162 0.0481 0.016 0.079 0.10 0.4300 4.6325 0.0928 0.053 0.123 0.15 0.6675 4.9487 0.1349 0.105 0.158 0.20 0.9200 5.2649 0.1747 0.173 0.188 0.25 1.1875 5.5811 0.2128 0.254 0.214 0.30 1.4700 5.8974 0.2493 0.350 0.238 0.35 1.7675 6.2136 0.2845 0.459 0.260 0.40 2.0800 6.5298 0.3185 0.583 0.280 0.45 2.4075 6.8460 0.3517 0.720 0.299 0.50 2.7500 7.1623 0.3840 0.872 0.317 0.55 3.1075 7.4785 0.4155 1.039 0.334 0.60 3.4800 7.7947 0.4465 1.221 0.351 0.65 3.8675 8.1110 0.4768 1.417 0.366 0.70 4.2700 8.4272 0.5067 1.630 0.382 0.75 4.6875 8.7434 0.5361 1.857 0.396 0.80 5.1200 9.0596 0.5651 2.101 0.410 0.85 5.5675 9.3759 0.5938 2.362 0.424 0.90 6.0300 9.6921 0.6222 2.639 0.438 0.95 6.5075 10.0083 0.6502 2.933 0.451 1.00 7.0000 10.324 00.6780 3.244 0.463 1.10 8.0300 10.9570 0.7329 3.919 0.488 1.20 9.1200 11.5895 0.7869 4.667 0.512 1.30 10.2700 12.2219 0.8403 5.491 0.535 1.40 11.4800 12,8544 0.8931 6.392 1 0.557 1.50 12.7500 13.4868 0.9454 7.374 0.578 1.60 14.0800 14.1193 0.9972 8.438 0.599 1.70 15.4700 14.7517 1.0487 9.588 0.620 1.80 16.9200 15.3842 1.0998 10.825 0.640 1.90 18.4300 1 16.0167 1.1507 12.151 0.659 2.00 20.0000 16.6491 1 1.2013 13.570 1 0.679 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 4.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB k: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FT/FT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.2325 4.8162 0.0483 0.019 0.080 0.10 0.4800 5.1325 0.0935 0.059 0.124 0.15 0.7425 5.4487 0.1363 0.118 0.159 0.20 1.0200 5.7649 0.1769 0.193 0.189 0.25 1.3125 6.0811 0.2158 0.284 0.216 0.30 1.6200 6.3974 0.2532 0.389 0.240 0.35 1.9425 6.7136 0.2893 0.510 0.263 0.40 2.2800 7.0298 0.3243 0.646 0.283 0.45 2.6325 7.3460 0.3584 0.797 0.303 0.50 3.0000 7.6623 0.3915 0.964 0.321 0.55 3.3825 7.9785 0.4240 1.146 0.339 0.60 3.7800 8.2947 0.4557 1.344 0.356 0.65 4.1925 8.6110 0.4869 1.558 0.372 0.70 4.6200 8.9272 0.5175 1.788 0.387 0.75 5.0625 9.2434 0.5477 2.035 0.402 0.80 5.5200 9.5596 0.5774 2.298 0.416 0.85 5.9925 9.8759 0.6068 2.579 0.430 0.90 6.4800 10.1921 0.6358 2.877 0.444 0.95 6.9825 10.5083 0.6645 3.192 0.457 1.00 7.5000 10.8246 0.6929 3.526 0.470 1.10 8.5800 11.4570 0.7489 4.248 0.495 1.20 9.7200 12.0895 0.8040 5.046 0.519 1.30 10.9200 12.7219 0.8584 5.922 0.542 1.40 12.1900 13.3544 0.9121 6.878 0.565 1.50 13.5000 13.9868 0.9652 7.917 0.586 1.60 14.8800 14.6193 1.0178 9.040 0.608 1.70 16.3200 15.2517 1.0700 10.251 0.628 1.80 17.8200 15.8842 1.1219 11.552 0.648 1.90 1 19.3800 16.5167 1.1734 12.945 10.668 2.00 21.0000 17.1491 1.2246 14.432 0.687 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FI')= 5.00 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(FT/FT)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.2575 5.3162 0.0484 0.021 0.080 0.10 0.5300 5.6325 0.0941 0.066 0.124 0.15 0.8175 5.9487 0.1374 0.131 0.160 0.20 1.1200 6.2649 0.1788 0.213 0.191 0.25 1.4375 6.5811 0.2184 0.313 0.218 0.30 1.7700 6.8974 0.2566 0.429 0.242 0.35 2.1175 7.2136 0.2935 0.562 0.265 0.40 2.4800 7.5298 0.3294 0.710 0.286 0.45 2.8575 7.8460 0.3642 0.875 0.306 0.50 3.2500 8.1623 0.3992 1.056 0.325 0.55 3.6575 8.4785 0.4314 1.254 0.343 0.60 4.0800 8.7947 0.4639 1.468 0.360 0.65 4.5175 9.1110 0.4958 1.699 0.376 0.70 4.9700 9.4272 0.5272 1.947 0.392 0.75 5.4375 9.7434 0.5581 2.213 0.407 0.80 5.9200 10.0596 0.5885 1 2.496 0.422 0.85 6.4175 10.3759 0.6185 2.797 0.436 0.90 6.9300 10.6921 0.6481 3.116 0.450 0.95 7.4575 11.0083 0.6774 3.454 0.463 1.00 8.0000 11.3246 0.7064 3.810 0.476 1.10 9.1300 11.9570 0.7636 4.580 0.502 1.20 10.3200 12.5895 0.8197 5.427 0.526 1.30 11.5700 13.2219 0.8751 6.356 0.549 1.40 12.8800 13.8544 0.9297 7.367 0.572 1.50 14.2500 14.4868 0.9837 8.463 0.594 1.60 15.6800 15.1193 1.0371 9.646 0.615 1.70 17.1700 15.7517 1.0900 10.919 0.636 1.80 18.7200 16.3842 1.1426 12.285 0.656 1.90 20.3300 17.0167 1.1947 13.744 0.676 2.00 22.0000 1 17.6491 1.2465 15.300 0.695 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 DITCH FLOW ANALYSIS BIOFILTRATION CALCULATION DITCH DATA: BOTTOM WIDTH(FT)= 5.50 JOB NAME: LEFT SIDE SLOPE(L:1)= 3.00 JOB#: RIGHT SIDE SLOPE(R:1)= 3.00 OPERATOR: BOTTOM SLOPE(Ff/FI)= 0.0200 DATE: MANNING'S n= 0.350 FLOW FLOW WETTED HYDRAULIC DITCH FLOW DEPTH AREA PERIMETER RADIUS CAPACITY VELOCITY (FEET) (SQ FT) (FEET) (FEET) (CFS) (FPS) 0.00 0.0000 0.0000 0.0000 0.000 0.000 0.05 0.2825 5.8162 0.0486 0.023 0.080 0.10 0.5800 6.1325 0.0946 0.072 0.125 0.15 0.8925 6.4487 0.1384 0.143 0.161 0.20 1.2200 6.7649 0.1803 0.234 0.192 0.25 1.5625 7.0811 0.2207 0.343 0.219 0.30 1.9200 7.3974 0.2596 0.469 0.244 0.35 2.2925 7.7136 0.2972 0.613 0.267 0.40 2.6800 8.0298 0.3338 0.774 0.289 0.45 3.0825 8.3460 0.3693 0.953 0.309 0.50 3.5000 8.6623 0.4041 1.149 0.328 0.55 3.9325 8.9785 0.4380 1.362 0.346 0.60 4.3800 9.2947 0.4712 1.593 0.364 0.65 4.8425 9.6110 0.5039 1.841 0.380 0.70 5.3200 9.9272 0.5359 2.108 0.396 0.75 5.8125 10.2434 0.5674 2.392 0.412 0.80 6.3200 10.5596 0.5985 2.695 0.426 0.85 6.8425 10.8759 0.6291 3.017 0.441 0.90 7.3800 11.1921 0.6594 3.357 0.455 0.95 7.9325 11.5083 0.6893 3.717 0.469 1.00 8.5000 11.8246 0.7188 4.096 0.482 1.10 9.6800 12.4570 0.7771 4.913 0.508 1.20 10.9200 13.0895 0.8343 5.811 0.532 1.30 12.2200 13.7219 0.8905 6.792 0.556 1.40 13.5800 14.3544 0.9461 7.858 0.579 1.50 15.0000 14.9868 1.0009 9.012 0.601 1.60 16.4800 15.6193 1.0551 10.255 1 0.622 1.70 18.0200 16.2517 1.1088 11.591 0.643 1.80 19.6200 16.8942 1.1620 13.021 0.664 1.90 21.2800 17.5167 1.2148 14.547 0.684 2.00 23.0000 18.1491 1.2673 16.172 0.703 20-Mar-92 DODDS ENGINEERS,INC. PAGE 1 G. WETPOND CONCEPTUAL DESIGN CALCULATIONS G. WETPOND CONCEPTUAL DESIGN CALCULATIONS The sub-basin "G" from the biofiltration swale analysis in Section F, is tributary to the wetpond located east of the large central wetland. The basin results summary shows that the volume of the P2/3 storm for this basin (G-3") is 9596 cubic feet. Additionally, the impervious area in the sub-basin is 5.02 ac. or 218,670 sq. ft. Per the K.C.S.W.D. manual, the wetpond must have three bays with a combined surface area of 1% of the impervious area and a combined volume equal to the P2/3 storm. The attached plan shows the proposed wetpond configuration. All of the bays will have a 3' depth of water storage. Bay #1: Water Surface Area = 1950 sq. ft. Pond Bottom Area = 165 sq. ft. Volume = 3172 cu. ft. Bay #2: Water Surface Area = 3010 sq. ft. Pond Bottom Area = 1070 sq. ft. Volume = 6120 cu. ft. Bay #3 Water Surface Area = 2335 sq. ft. Pond Bottom Area = 770 sq. ft. Volume = 4657 cu. ft. Total Surface Area = 7295 sq. ft. > 2,187 sq. ft. OK! Total Volume = 13,949 cu. ft. > 9,596 cu. ft. OK! ( T YPo ) • . �;:rt��--..fir.;�`� �.� ;�,��';' .��,1 � � •,� '•"• �+` t� • ;:�; ;: :•:.. . . • . : ; • . . . . . . . s • � :ram �.' •� � �� •' � . . . . . r• l . . ... •�'•�• .�• '�•�' •fir. •�• * .!.' . . :� � . . . . . . . . . . N -X. All ROP OSED H. LEVEL 1 OFF-SITE ANALYSIS 1 H. LEVEL 1 OFF-SITE ANALYSIS 1. WEST BASIN The west basin discharges across the south property line of Sector A fronting Union Ave NE. Drainage flows southerly offsite through a wide open swale for approximately 250 feet before crossing beneath a gravel driveway via an 18 inch vitrified clay pipe. The pipe crown is damaged and is bridged by a steel half-round culvert. The culvert is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southerly for 350 feet in the swale before crossing beneath another gravel driveway via an 18 inch concrete culvert. The pipe is in good condition but is filled with 6 inches of sediment. No obvious evidence existed to show that the gravel driveway had been overtopped by drainage flows. Drainage continues southwesterly for 250 feet before being intercepted by a 24" culvert that is stubbed out from the Union Avenue N.E. trunk, which is also 24" in size. From this point the runoff flows south in the Union Avenue storm drainage system. 2. EAST BASIN The areas to be analyzed or discussed in more detail are indicated by [#]. Runoff from the northern portion of the east basin (north of N.E. 6th Street) crosses Duvall Avenue N.E. to the east in an 18" concrete culvert [1] at the 6th Street intersection. The runoff from the remainder of the offsite area and the onsite area east of Duvall Avenue, joins this flow in the roadside ditch and existing wetland area, continuing to the south for 650'. It then crosses back under Duvall Avenue to the west in a 36" concrete culvert [2]. On the west side of the road at the south edge of the site, runoff from the remaining onsite area is added and the flow is directed south for 80' in a 36" CMP culvert [3]. The culvert discharges into an open swale, flowing southwest for approximately 600' where it is received by a 30" CMP culvert system [4] conveying it through the ..� Windsor Place Apartments for 370' to the west property line of Windsor Place. From here the flow is directed into a rocked channel that flows 150' westerly to a pair of 20' culverts[5], one 12" and one 18", crossing an old access road. The rocked channel then continues southwesterly for 170' to an 18" concrete culvert [6]approximately 30' long, crossing an access road to a water pump house along N.E. 4th Street. The culvert discharges into a short section of open swale leading to a 36" concrete culvert [7] crossing N.E. 4th Street to the south. From here the flows enter a channel [8] leading west along 4th Street for approximately 100' and it then turns and continues to the south. From the previous drainage analysis and additional downstream basin analysis up to the Windsor Place Apartments, the following peak flow rates were obtained: 10 year developed = 4.7 cfs 100 year developed = 16.3 cfs 100 year existing = 25.2 cfs [1] 18" concrete culvert crossing Duvall Avenue N.E. - This culvert is listed in the Maplewood Drainage Basin Study as having capacity problems for 100 year events. The slope is 0.6%, length is 85'. The capacity is 8.8 cfs flowing full. There is approximately 3' of headwater depth available to push more flow through the pipe. However, this culvert will be replaced and resized as part of the Orchards development, so capacity will not be an issue. [2] 36" concrete culvert crossing Duvall Avenue N.E. - The slope is 2.3%, length is 110'. Capacity is 119.6 cfs flowing full, or 35 cfs with no headwater over the pipe entrance. Therefore, capacity is not a problem. [3] 36" CMP culvert along west side of Duvall Avenue N.E. - The slope is 1%, length is 80'. Capacity is 36.1 cfs flowing full, or 35 cfs with no headwater over the top of the pipe entrance. Therefore, capacity is not a problem. [4] 30"CMP culvert system through Windsor Place -The minimum slope is 0.8%. The capacity flowing full is 19.9 cfs. This is also listed as a flooding problem. While some headwater buildup would be necessary to convey the existing 100 year storm event, the reduced flow from the Orchards detention system should not be a capacity problem. There are some constrictions placed in the open channel, presumably by the property owner, leading to the culvert which may cause some "r minor flooding, but nothing of concern. Specifically, a 12" pipe under a small trail would cause the flows to overtop the trail, but the flow would still be contained. [5] 12" and 18" culverts in rocked channel. - The Windsor Place plans show that these culverts were to be abandoned and the channel was to go through the existing access road. The road was to be blocked off. However, even if the flows must overtop the road due to culvert capacity problems, they would easily be contained within the immediate area of the swale. [6] 18" concrete culvert at the water pump house - The slope is approximately 2%. The capacity is 16.1 cfs. There will be a slight headwater buildup to convey the 100 year storm event, and the available headwater depth is more than adequate. [7] 36" concrete culvert crossing N.E. 4th Street - The slope is 0.5%. The capacity is 51 cfs flowing full. Capacity is not a problem. [8] Channel along N.E. 4th Street - This is also listed as being restricted by the Maplewood Drainage Basin Study. The study calls for reconstruction of the channel. Our field inspection verifies this observation. The channel has a negative slope of approximately 2' along 4th Street before it turns to the south. It has adequate depth but needs to be regraded. As it exists, it still has the capacity to convey the 100 year storm, but would likely cause water to back up though to the north side of N.E. 4th Street. In a City of Renton memo to Mary Lynn Myer from Randall Parsons, dated January 21, 1991, the drainage concerns above, along with erosion problems further downstream, were discussed. The recommendation was made to over-detain on the Orchards project for the 2-year storm (releasing at 50% of the existing 2-year peak flow rate) and for the 10-year storm (releasing at the existing 2-year peak flow rate). Additionally, the existing 100-year peak flow rate would have to be matched or decreased for the developed 100-year storm event. These criteria have been met or exceeded by this preliminary design for the Orchards project. FOR DISTRIBUTION TO: Water Utility Building Dlvision Wastewater Utility Public Works Constr Inspector Surface Water Utility Fire Prevention Maintenance Servlees Transportadon Systcros Project: QZC14A-eus, — L1t6 �2y Location:&A-ST— 571DA— 6 Er DUf/,aLL_4LJ NC A(cached please find copies of: �fq PERMIT ® BILLS OF SALE -. RECEIPT ® COST DATA INVENTORY .I LETTER OF SPECIAL BILLING ® BASEMENT(S) STUB SERVICE AGREEMENT ® COPY OF AS•BUILT PRECON NOTES ® - PRECON ATTENDEES DRAINAGE REPORT trtEMO • WATER BREAKDOWN MAP WITH NEW MAINS AND VALVES OTHER From: DODDS ENGINEERS, INC. -a CIVIL ENGINF EYING S U R V EYING PLANNING STORM DRAINAGE REPORT FOR THE ORCHARDS - BLUEBERRY LANE RENTON, WASHINGTON Prepared by: David E. Cayton, P.E. �T. Approved by: Edgar T. Jones P.E. Date: April 2, 1997 t DEI#: 95127 = z" I to JS NA exrwes 4-• 3.9-7 4205 1 48TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 (206) 885-7877 FAX: (206) 885-7963 This proposed project will include the development of a 10 acre parcel of land located within the City of Renton. The project site is located on the east side of Duvall Ave. NE approximately 600 feet north of NE 4th St. This development will include constructing 57 single family townhomes, private roadways, a public roadway and utilities to support the above mentioned units. This project, formerly referred to as Sector G, is a continuation of The Orchards, a 62.3 acre Northward Properties development that has been constructed in phases since 1994. The initial storm drainage analysis was performed in April of 1994 and included the entire Orchards project. This analysis included using the existing on-site wetlands for detention and incorporated bio-swales for water quality enhancement. A portion of this analysis and a basin map are included in this report. For a complete detailed explanation, see "Storm Drainage Calculations for The Orchards", a study performed by this office, dated April 4, 1994. The storm water detention and water quality facilities for this project were constructed in conjunction with The Orchards - Division 1 and were completed in 1995. These facilities are located in the west half of the site and were designed to control runoff from approximately 46 acres, including the Blueberry Lane development and all off-site tributary area. See the above mentioned report for detention calculations The storm drainage improvements for this project will include 2 pipe/catch basin networks that will route all runoff, including rooftops, to the existing wetland. Part of this system will include constructing 2 bio-swales, 1 at each outfall, that will treat the runoff prior to its release into the wetland. The outfall elevation of each bio-swale will be set equal to the calculated maximum water surface elevation of the wetland during the 2 year, 24 hour design storm. This storm drainage system will also include a series of yard drains that will be placed behind the uphill buildings to provide adequate rear yard drainage and to intercept runoff from approximately 7.65 acres of offsite tributary area east of the site, see the attached offsite basin map. Backwater calculations were performed in accordance with the King County Surface Water Design Manual. These calculations include routing all developed on-site and off- site tributary runoff through the developed storm drainage system. The 25 year, 24 hour design storm was used to size the conveyance system, see attached spreadsheet. Ss. -�Z JK 24 156LF e'o da?Z„ t � ! •.D t-m �„ BLUEBERRY LANE CB 12 STORM DRAINAGE SYSTEM _ �.'.AP �45EEGEiA,'L � ►=�`<y. ,. "--.�.�,;� �.,�-� �'. ,�! i� 0 20 a 810 SI'1 CO C 1 1 STA 5+66.E3, P. Ri. ( - � c. 7 � T rE 1, 7.'-.RsU C.'�.=.: G=ACB 5 CB 10 �12LF6' YDI 11A � .' STA 2+07, 18.17°RT. rtP 2, i ' TYPE r SEP�,4AT04 i f� r i 75LF 12'CpEp �`'4^i-. _ ... /E 6'J9714 �2 -\�� s,;;. J97.14 � _ � `, � ', 18' D/A. RIM 405.8 } '� `� _ 3- o ;' ►zl �c d �a: lE 6- 403.94 4 CB OUTFACE 10A STA 2+97. 9.1T RT. TYPE 1 lE 12-J94.82 SEE DETAIL - 8,'Gr7L TPA VON SWALE SEE DETAIL SHT. Co r 18' D/A. _ '�• � RIM 405.0 IE 8' 403.07 t r \ n t;` + .i � `� - '�f; } lE 6' 40J.07 CB 2 r STA 6+50, 1-5 P.T. >.c : - �+ 7 T?E 1, i HP.U CU,49 G?A i \ - _ :�: ;r t- �,� CB J OUTFACE -,L. ` _ _ �.��, �' LOCATE 0 612 1A ry� `. l " ? 25.8'RT. ir-w' j - '' (� TYPE 1 lE 12':9487 D F-/•o3�F P,P-R"P - S__DET.:IL 1?J j 1i t i c SHT Cc B;Gr�Lr?.ATiON Si'/FiE � — < W 'r \\ + s- cc. SE.0,-TAX SH T. CB '� l \ 1 c SL•= O.005G J - \ i' li -= !Pei p6• t'C-; C Z- O.JL1W4 r--R ; ;.t .! � ":;ram 6• 'l � T' i� SEPAPA TOR �1 r;fi t- ._- SEe DETAIL I j y \' •i;�. •�.fi /.�' j� _ -: { \ 8C t I •. `� \.` V.'(� �v :/ at�rf' o RIM 400.2 - j /E 8' J98.07 SRIS \�' f\ y. "'�,• 3' Vic'`•\'- -_____ - ry! '�� � CB 88 -t ; .� �'.;." ..N• 'ST -: . .�- - TYPE r RIM J99.2 �. !/� % f' ` •'�j- ` 1 // `. - �s /£ 8& 12'J9704 i _____________----__--____________ TYPE 1 _ p • RIM 400.5 T O_ - f '.- _ CB I£ 12'396.85 ii 0 r-3 im �__ �_- =',Y�=;�:. �: ==-==_=:��'�--- - -yam 1► 1I II .• , �, r 1• ,�'•R a•l�'': ' .I rr. . I ail •., - I� nr A .,. 1'•:t Mrpa t ll .:.: " : If ta•r 34 �i 44a. [. �' r Ila• T11• Ilit7r'ft. 1�,•wt p r� - _..•,- /2f- ---'-- • .-_ -- .alit. �r>_ ID•+•�. .'v. x ' 77 �I0A 0 0 M � tl O 7. I' `• I iR it 1'�, T^ i1 �418 .. t,1 '• i © ,•r.l. '+v. '' I �, rtra/1+�aY�l x.17 , ■ 11 i T [! 1 j1 I •I I I 1 x 413Lvov- " It !•� 1 1 7 it 423 xalt Q• ; ; I 1. .. �' �. I'� ^. ` 404 NN 13 `- .T j ,IfpKEro[w cl cy+•,+etlwo4 . �',� •' I p ( ` I' R. LL��' 1 'r ''' •• ',,IOS I,• i'' t xIl�.-max , yf-... T11 A / ;�'!Z;jf"• 4t�it 5rit, 1�'r �, 1••-r--" x. � r•.� � w`i.,.;,�� •.,�� f�t: I �.1" '� �;,. .�• o p �1 Ir .. :,;•.�,; •1,�,•,�t,.�.r.:}�i. � •. � f e tol �I• .. i'� !� �•• ,v f•�'t� as-1`� fs •1.. •'�y,J.:l�: �„"S;�•i�� '' �;�;•• ' :•i,.r, t --�` . : `' '`' +� :. .• ,.! •• 0 ��,J( Ix 472 rm 411 a _. T ca :; / Put rr - .. ��-'• :•�:• • .! '�'"' _ ', _ 1 �� •. (gip, n I • .. •'� '•. 1 Ii '• .. ill (03 TREES 1 0 r_••• '•`� •' 'O (•'(_ •� J � ':: .,�i t' !• ' ra �•� t1.S••'•, ' .. I .pl.I I� .,'"a , , r= rtS y��';W,r.� .t.. r—•ram ••�' �1 • ',• :, a.1ir.1!'t, .pt � •I1 rtl!.;1�p•!';'' .�} `1•e;'r Q "•r% t, •+R[27, .r_• //s• .1t�0f' . � • 7^ ..•�• •t.t sr�r.` ,. .• . _ - ... - •,. '' ..• I any �, .+, T; ��:• 'r;• ,1 , , - - -- .�::,•,.�, ��" ,'I';�;' p i 'r• t.,.a'.i'J�Irt .}.,1;•t• s: l' .I. .`l�" �'•' �*O I a T�,�•' I .. I ' r .f fll y)'I� • , ••i •t --�. �� t t,. �yly,,�•.v,w1y:1•-r•� .,, •, '•., ••• i •:-:''.`rr`n�,�'/•". z: �: �7=J'1'S�1' t t �t• TR, .. � :r•.�,.li•...�':.�r,•t.'/�•J'1 ;,i, 5/. I� •r• �, „ �e x .I , � '.a., tf Jf:,•� :.}'w'Y,•1�:�7'•a1.ltT �r: •1 , :•: dR11711; �' ..•. .yo .,L I x :'.i' '• ' e i.,is•'••!•:.I.,'.'r: v. .,i. ;� �. -�. If 13 • x (� �• Ii-+ ' ..��;! ` �� •I '`t•' ''1''• •�•• Nip°�fl lln ilk, ' Dom' BRUSH . rr: x411 ;r 11` ,ir:1 : .• •1�,•:'.�• F�. ri ' i ,t. ./. �Ki[!' ! ii .. .• - y.-.--w �L.�. ' •fit' •�:• ;}�•�%�.��;�•�tt�' I_� 't• •,. ;i 400 ,•r• '1•i I'' ,.r• -^- (G I '• � , 'i1, ,ty 'i�?'/•r ,r TR[ 3•,' ,. • iR�Ca 't. 1 ; • �.--�_•`� .,• '• 'x]•III '.��,. ',• •.�• .'� I I M. 't. ,1 ,Y r ••• .r'. '. I1 T11 t� Y.,i ' '!�. r•• O OR t . . (p ..��'11.. 1 ... I i -�h� •rii• f•• /•1• rIJ'.•• •, T 1._7 II ., II��:� -1,... _ I 1 .•U�r-----"'ice _ '• �a�:•tf"t••: .' / ::, Cl) (• '�� _ '1st.'" r.a ly +; ,� II 1 ► - I, li - , ; t I -IibbUAl►116r,' f 11 m 4Tj iaa ------- - -- --- -- 1�-- -- - - �� ---i( T -- - lanoa �wK • z� —'I • ' �r y r, 1.�r: i.' ;i 1 1,`,Z..r p) , e', J p i s r11,12a,aS• ' —� ` 1 Y r r! .'',�•v,?:;1/i9t i 11J , '.l1� � 1 � �' ' '.1 � �t'� ...;;.di t •'1,�11 It �i,a'�FII.t:• �• ,tit� :; •i•::J, aAa,:r:Itr3KuDrti N. ,iS� n urban planning -. I pirn•lalona o/Sacflai It:.'ji''i �.Prq(atlRJf. ;,.,. f:r• c.:....w••.r-a►.w• 'j •;• >w' h Raclangul0,grid�aCOd brl►arlilbiil prD�INIDrY S, Cl)cn N a ��'' ':-tea"'� w•. i. �• f 1 al: ''1 (( 1 % 1 ,� l: �/x• 1\•. •^. / ���.�.-... {��•�.1 �u� t T' ra• r � �1 .41"I� III-Ir 1 •1 f / Imo'' _ / I. /�•1 \ .11 _ \�16 •., ' �. 01 tom'"1.4,1,"I�h ��tll/ •:li ':�•"' 1 .�.!1.1. .._I, rI '� '•� �_,.rr� - Y��r I �� 1 \.. ::• .•?-JK 7. .i .a:. 1 u 1 .. •1 'I1 f�'��n: 1•:I �•1 � j� �: •1 .�..�:. .r.' .r•/-• I• •r• .•\'' � �' f •r i^ � N a rro•rrvr. 'Y � is� ll t, 11 .s'i� :r, r ' •• '" - ...�_v � I tr/. I 1',I:_ 1I '`ll _,,_- ,/ � M't ••'� I •i •r J,r. -) ^u::�s .� - - '_+.. ! Y 1 I • L,�'�� '1 I"I;` 111 n• •I ,\ •, n/C.�:.,� .-•C �o! ,���\r,_ �a , 1 r�:.C-Ilc \" ♦ - 11 O, _��1:i. -''r 'h:r 1 �;�iy.�f� r•�}Y� �„ I ♦ L. .IIiI�!'—..1.__� r�(•F.� (� •�1 , :�,.. l.i\'%.. ./� ;.',f _.--:-'_�• , .. �„r` •..� —"-� •1 ••?�.1. I� -��` IIr ll Ll�,1J. i •Ij' •� �'���- ",�r::, �.•, !; /'/\j/� ;; ;,;r., ..._ --1 l — IIr a _N.I,, ��I Ltta J Iii �` t',,' ;• •,1'"• ;t• w,�� )1 '�r�� ��•.• •1 a III) �\ •"� 'r \. ;I "� i-/ 1 _ '1 / ■ - � -_ . 'I� - ') - --may �• r � - � ' •:- �..� ..�• ..y ..� a f'I:•:ff••',Y I 4 I ti r' �:- .'"- - �• '-'_.- - _ ea � I � I ,a iv •` •Ir S�ji-:x--�^ra�'.• / j" ?a'da•''F' _`il� s.--(.n�'Y s���y_1'..I\ —;__' ��• / /\�' ...�• � ,_1::. Jh .l_j._ �. !!c J.:1 •` .� .\ �'•jty:� �'yy- ..+ •�. ,• 'f 1 V I l a _ •/ I. [_I �,I riC;� �—_�• (' / �',\?'� ~ Is \I •/::«,i •t (7 i•f�c�s-i-+�° 4 ;r •�.._. I'I I1 =ia_• �_ \-�. \{ 11 ••'�� I\ { -�.•l��• �, .l.Y II, .I'� -_�•- }"I" .;'�'. I f_..a. .i' J'\ "�' I i �A f• r•� I f rr a� �.. Y _...{ •r. ��-� \ 1 I�'. _� r�11II'�'1 .: _ ,�� 111�-M•- _ _1.:,� ..�.�-•,•'•r j ''! �� �r "r.. •I ;��.....� �.._ tj '- ?I.iI IIII//'ll II - Iff,~ I�...-_./ I.l\II.i J'I�I• A•.•I;II�'I�I I�.IJ\ Ij..l wa� I I�'' • �1i',/!�{�; �.,r' ri I •V 1 � - 1�� �, / t.�, 1 .. _/ ', •_ � ���'I•,I 1 �..I�• I �'�lJ r' r:�._ f I .,,, �•r''J: ,,• 1 � - -. . II. 1� L—r' 1�lII (' 1 � ra �a j.. IIi 'j' �` .r ( •••••---••-�•'''""''' r 1/111LL_��....L---..JL!l��� �'.•� r �r/1 ,���. !f 1 •i' .i �' J ,.�. ' , � 1 ill. ��9 l'�-I S I•` I I' •i all� �� f � t. � _ "� �� •� /•� / � �� �i - .LaX�.111 rr^I r r': e•� •�/^'ems":\1'.,;.1. .,\ _ �h. l..•..I-_�� \•�• ..✓ -•:i::�:r..•-1 "P�-: -� j/ �: Jry a!J• _ ,r' C 1 i� 'J."Tf•'l E�-•,� '._I a�•• i •r �� + ' -�•.. ram• `N .. 11 !I • i- -- /r N a• •/• 1 I. �'�,►, Ir•�) \ _ ~�_� �,rr-'r '�j`� ter•; .r•.r+,`� r I. i" � _ L, - �.Y�-.�J ;� -� �I�r r_- j ,i /.":f '/ �'��.:��--i � •.�•'.::�••:' -;1! .f.• . ..,Ca . 1'll -S• ti' •�1''�I •I j 11�,..,-�✓. � _ e.: .'L•.i t •` •"r i J._._�_� �•_�rf( _,1•.Yt�. �I `C _1_�. /'Irt _.I '�'•fJ!r�tl�r,•,I.�r ja"te��• 1N� �.r Y•• ( I 11 - _� .- _ 1 __ � 1. �I l _. Ir - - q [, i {�w��t' r "r•ar �• • •• r•.� "( _ 'r---;•r— �1I+ '� :r ''S �--_•=„_.,;, _�\ I. "•� 4 v '. • 'i\.'y.,\•,.l�r tti� ..r.•:r.{z.a:•.. � 1 1 Fi -a�1 , ,)i/ •I�1 1.11. �1I /�`\ —�-c _ _ 1 a \\ 1' ♦ •. �\ .-.a:. r•_ra'•' v. ♦ , •` 1.11 I.�.7� �� �• �• ' ��: I I,:.I "\.` _.i—.r_. - S 4 I •.I\ /`\/\� \ �,Cw v ••.' _:i-..�i_�. .«i��,•�:... :I•N i{ I�. a ,., 1 ).:. - - __ - ,•- ._ _.•:.- -.... O.__•._— •� �`=� -�r � I�r��i �,r.� pr t i, ,il_• 3a J—� ,((1 it � ,� � `a —•-,is���---- ,� 1 Ul � OYJVAL�•.AVE. S Ilf. i': 'I Ii. ..�:.a_:=:.1=/ .t.ou •.'t 4. '_^_•i oo'oo'lt.� .ter, '♦ � -_ — — D VALL AVE S E. ?��.'����� 1 �T' •°�"�.�.��_ale:'��• ,I `r. 011 .... vt 1 O iJI`m O it I� ` - N Alki AT I- -k 10 ' '_ :��-- �_,c--�:s�• • _� :=Neff• - m co rn N N o _ a Z o � D "' «v D N Z TIIIS DATA WAS TAKEN FROM TIIE ORCHARDS, DIVISION 1 STORM DRAINAGE REPORT, DATED APRIL 49 1994 4. DEVELOPED SITE HYDROLOGY As previously discussed, the developed drainage system will continue to split the site into two drainage basllls. a. WEST BASIN: The proposed design for the west basin involves the use of the existing wetland #1 for detention. Due to site constraints, a developed area slightly less than the existing west basin will be tributary to the detention system. The remaining area will be directed to the main cast detention pond, but the developed discharges will be designed to match the existing peltk flows of either basin. R "Z": 13.6 acres, tributary to main west detention system (100) 4.70 ac, impervious @ CN = 98 7.20 ac, landscapinl,/wetland/brush @ CN = 84.5 Time of Concentration: estimated at 25 minutes b. EAST BASIN: The developed cast basin will be divided into three sub-basins, each tributary to one of the enhanced wetlands to be used for storm drainage detention/water quality facilities. "V": 2.80 acres, tributary to the southeast detention system (300) 1.22 ac, impervious @ CN = 98 1.60 ac, landscape/brush @ CN = 85 Time of Concentration: estimated at 20 minutes "W": 8.1 acres, tributary to the second wetland (400) 3.6 ac, impervious @ CN = 98 4.5 ac, landscaping/brush/wetland c, CN = 85 Time of Concentration: estimated at 25 minutes "X": 14.52 acres, tributary to the first wetland (200) 4.72 ac, impervious a CN = 98 9.8 ac, landscaping/brush/wetland a CN = 85 Time of Concentration: estimated at 30 minutes "Y": 23.3 acres, tributary to the third wetland (300) 10.4 ac, impervious a CN = 98 12.9 ac, landscaping/brush/wetland @ CN = 85 Time of,Concentration: estimated at 30 minutes A developed drainage map is included in this section along with Basin Summary printouts and basin flow summaries. BACK-WATER CALCULATIONS JOB NAME: ORCHARDS-BLUEBERRY LANE PREPARED BY: DAVID E.CAl?ON JOB NUMBER: 95127 -DESIGN 570R11: '_S YEAR ENTRANCE ENTRANCE EXIT OUTLET INLET APPROACH BE JUNCTION PIPE PIPE h'IANNING'S OUTLF7 INLET PIPE FLOR' \'ELOCITI' 7AIG\FATFR FRICTION HGL HEAD HEAD CONTROL CONTROL VELOCITY HEAD HBAD HEADWATER FROM TO FI.o\\' LENGTH DIA. a ELEVATION ELEVATION AREA V%I.00ITY H%AD ELEVATION LOSS sLEvanoN LOSS LOSS ELEVATION ELEVATION HEAD LOSS LOSS. ELEVATION CB CB CFS EE N \'ALL'% (FHHT) SET) (SQ ,SEC) (FEET) (FRET) (FEE (FEET) (FEET) (FEET) EST) (FEET) (FEE (FEET) HF (FEET) RIAt EL OLTP10 10 22 27 12 0.012 394.82 394.96 0.79 2.78 0.12 395.29 0.09 395.96 0,02 0.06 396.04 O.W 0.12 0.00 0.00 395.92 400.5 CB10 CBl1 2.2 75 12 0.012 394.E 395.33 0.79 2.78 0,12 395.92 0.24 396.33 0.06 0.06 3%.45 0.00 0.12 0.00 0.00 3%.33 34005 CB12 CB12 22 87 12 0.012 395.33 395.77 0.79 2.78 0.12 396.33 0.27 396.77 0.06 0.06 3%.89 0.00 0.00 0.12 0.00 397.01 400.69 12 CB13 2.2 53 12 0.012 395.77 3%.83 0.79 2.78 0.12 397.01 0.17 397.83 0.06 0.06 397.95 0.00 0.00 0.12 0.00 398.07 401.8 0 0 0.0 0 0 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CBII YDILA 0.3 34 8 0.012 39610 39734 0.35 0.83 0.01 3%.33 0.02 397.81 0.01 0.01 397.82 0.00 0.29 0.00 0.00 397.52 399.5 0 0 0.0 0 0 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0 0 0.0 0 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 OUTIA CBI 3.6 25 12 0.012 394.87 395.00 0.79 4.52 0.32 395.29 0.21 3%.00 0.16 0.16 3%.32 0.00 0.29 0.16 0.00 3%.18 400 CBI CB2 3.4 93 12 0.012 395.00 395.47 0.79 4.34 0.29 396.18 0.72 3%.90 0.15 0.15 397.20 0.00 0.19 0.29 0.00 397.30 398.04 CB2 CB6 2.77 74 12 0.012 395.47 395.54 0.79 3.49 0.19 397.30 OX 397.67 0.09 0.09 397.86 0.00 0.13 0.19 0.00 397.92 399.06 CB6 CB7 2.7 36 12 0.012 395.84 396.02 0.79 3.49 0.19 397.92 0.18 398.10 0.09 0.09 398.29 0.00 0.19 0.00 398.48 399.14 CB7 CBS 2. S7 12 0.012 396.02 3%.45 0.79 3.49 0.19 398.48 0.43 398.91 0.09 0.09 399.10 0.00- 0.13 0.19 0.00 399.6 400.3 CBS C88A 2.3 80 12 0.012 396.45 3%.85 0.79 2.98 0.13 399.16 0.27 399.43 0.06 0.06 399.56 0.00 0.00 0.13 0.00 399.69 400.5 C'BSA CBSB 2.3 38 12 0.012 396.85 397.04 0.79 2.88 0.13 399.69 0.13 399.81 0.06 0.06 399.94 0.00 0.00 0.00 0.00 399.94 399.2 C132 CB3 0.3 58 12 0.012 395.47 395.76 0.79 0.43 0.00 397.30 0.00 397.30 0.00 0.00 397.31 0.00 0.00 0.00 0.00 397.M 399.08 CB3 CB4 0.3 49 I2 0.012 395.76 399A3 0.19 0.43 0,00 397.30 0.00 400.43 0.00 0.00 400.43 0.00 0.00 0.00 0.00 400.CB4 CB5 0.3 92 12 0.012 399.43 399.90 0.79 OA3 0.00 400.43 0.01 400.90 0.00 0 43 402.69 .00 400.90 0.00 0.00 0.00 0.00 400.43 403.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0 CB6 CB9 0.3 97 12 0.012 395.94 396.32 0.79 0.43 0.00 3r792 0.01 397.93 0.00 0.00 391.93 0.00 0.00 0.00 0.00 397.93 399.73 0 0 0.0 0 0 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 `!2/97 DODDS ENGINEERS,INC. PAGE I f DODDS ENGINEERS, INC. CIVIL ENGINIF E_ RING SURVEYING PLANNING EROSION/SEDIMENTATION CONTROL CALCULATIONS FOR THE ORCHARDS SECTOR G RENTON, WASHINGTON Prepared by: David E. Cayton, P.E. �,��T• jO Approved by: Edgar T. Jones, P.E. ���,� •'W �,Yf Date: March 13, 1997 DEI#: 95127 ' y • cc EXPIRES 4205 'I 48TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 (206) 885-7877 FAX: (206) 885-7963 - - - J � Q � — DODDS ENGINEERS, INC. JOB NO. '?SIz7 CIVIL ENGINEERING SURVEYING PLANNING OATS 4205 146TH AVE. N.E., SUITE 200 - BELLEVUE, WA 98007 1 (2061 ©65-7677 OR 454-3743 BY A C C/ ,A V-1-'0A0 O K V-A 1z 1;---s 5� ( -r o a & 2 o 5S I o va C°o w -r 12 o L (*,01 L c' s. sv). r r SEb �1-�r-ry -r pov.� �> s (zrry 6 CAc. es 2-0 So1L -ryPc G fz Aj r LL Shr0 > `/ LOA v-i Hyt;i R-OL-Obl Err vvt� - C q C IRT� 7ReOFL L jr In, rat Soo (p 5�" -(�3C� � ASS(Artish� QZ = /, 0 6 J-> ( S .-r /477A-c-Ay t�� Sf} = Z C1L � O , 00 � 96 = z, ZOO src � EQu1R� CC ToP alv, rw- �DV'j T> Ibw (ti5 F Z 7 174- g z v-, ,�x) °� Fop LlS¢ 5 ,pr SLc7PG :5:- ( lrt/ 71'n /oR� ( OLA7e, N S'r t3.4 -5 T, h 1T> s7D0 A .�7DITP, 0s bEwrl7 1yot OvzI r tzlvo L-eD 10, 6 X -:56G) 0T90.s /O . b ,� bovC2 (3z, •s o SHEET ! OF Z 3/17/97 Dodds Engineers, Incorporated page 1 ORCHARDS SECTOR G DEI # 95127 DEC 3-13-97 - ------------ BASIN SUMMARY BASIN ID: EROS2 NAME : SEDIMENT POND SIZING, 2 YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 6 . 10 Acres BASEFLOWS : 0 . 00 cfs RAINFALL 'TYPE . . . . : TYPElA PERVIOUS AREA PRECIPITATION. . . . : 2 . 00 inches AREA. . : 6 . 10 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 87 . 00 TIME OF CONC. . . . . : 10 . 54 min IMPERVIOUS AREA ABSTRACTION COEFF: 0 . 20 AREA. . : 0 . 00 Acres CN. . . . : 98 . 00 TcReach - Sheet L: 300 . 00 ns : 0 . 0500 p2yr: 2 . 00 s : 0 . 0300 PEAK RATE : 1 . 06 cfs VOL: 0 .46 Ac-ft TIME : 480 min U w x � lF ^53ti 4r M ♦, Y` e ---- ® � D O D D S ENGINEERS, INC. C I VI L E NGI N E E R I N G S U R V E Y I N G R L A N N I N G July 10, 1991 DEI Project No. 88008 V Mr. Randall Parsons Utility Supervisor Utility Systems Division RlVT4y 2Ci of Renton 00 Dept. Mill Avenue ,South E none Renton, WA 98055 Subject: The Orchards Dear Randall: Attached are two copies of letters to The Ferris Company, preparers of The Orchards EIS, incorpoiating your comments during our meeting of June 11, 1991 regarding drain- age concerns for The Orchards. The following is a summary of that meeting: 1. Due to the existing erosion and flooding occurring in the vicinity of the Maple- wood Golf Course, the existing 2-year release rate should be reduced by 50% and the existing 10-year release rate should be reduced to the existing 2-year release rate. Storage will be computed under fully developed onsite conditions for the 2-year and 10-year storms releasing at the above respective release rates. 2. The flooding in the vicinity of Amantes Flower Shop should be investigated to see whether or not it is within The Orchard's downstream drainage basin. 3. An open corridor should be maintained for wetlands 3 and 4 with the corridor ex- tending to the existing 18-inch culvert discharging currently to wetland 7. The water level fluctuation in wetland 3 should be reduced as much as possible. Th;; use of wetlands 1, 4, and 7 for storm ',eater detention is permissible, provided biofiltration :is provided for runoff from asphalt. The biofiltration facilities may be located within tl':e wetland buffer areas. 4. The existing culvert crossing Ditvall r-venue S.E. should 1»ssibly be enlarged to accommodatke passage of small wetland manLmis. This is a bitter-sweet moment in the past 3 years we have been working on this pro- ject. The project is headed for another nietarnorphosis in response to regulation, re- quirement, and city personnel changes. However, we are encouraged by your interest in the project and your professional background that hopefully will aid in making this the last major site plan change. We look forward to working with you in refining the details of the drainage plan during the initigation agreement, staff report prepara- tion, public hearing, and working drawing phases of this project. 4205 148TH AVE. N.E., SUITE 200-BELLEVUE, WA 9B007 [2061 B85-7B77 OR 454-3743 FAX:[206)885-7963 Mr. Randall Parsons July 10, 1991 Page 2 of 2 If you have any questions regarding the attached or require more information in the future on this project, please do not hesitate to contact us. Sincerely, DODDS ENGINEERS, INC. 4j g T ones, E. ct ana r ETJ:cyd Enclosures cc: Craig Krueger, Northward =- Q DODDS ENGINEERS, INC. CIVIL ENGINEERING S U R V E Y I N G P L A N N I N G July 9, 1991 DEI Project No. 88008 Mr. Rich Schipanski The Ferris Company 10655 N.E. 4th Street Suite 506 Bellevue, WA 98004 Subject: The Orchards,Renton Dear Rich: I have attached a copy of "The Orchards Downstream Drainage Basin Boundary" exhibit for the above-referenced project. This is provided for clarification of the separa- tion that occurs between the drainage basin downstream of The Orchards and the drain- age basin that is east of The Orchards. As is indicated on the attached exhibit, the drainage basin boundary (i.e. a ridge or rise in the ground elevation that directs rainfall runoff into separate drainage basins) runs in a southwesterly direction from the southeastern project site corner to the intersection of Duvall Avenue N.E. and N.E. 4th Street. The drainage basin boundary continues west along N.E. 4th Street then turns south. The discharge from The Orchards is contained to the north and west of this boundary within a culvert system and open swale (refer to the swale arrows marked "Orchards Downstream" on the attached exhibit). The flooding problems in the vicinity of the existing flower shop as described by Mr. Baldwin and Mr. Montgomery, at the May 14, 1991 public hearing regarding the EIS for The Orchards, occur at culvert "A" shown on the attached exhibit. The culvert is approximately 600-feet east of the intersection of Duvall Avenue N.E. and N.E. 4th Street. Mr. Baldwin also described some other drainage problems approximately 1/ mile south of this culvert "A". As indicated on the attached exhibit, these problems exist within the drainage basin to the east of The Orchards Downstream Drainage Basin. Both problem areas are south and east of the drainage basin boundary that separates the two basins. 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE, WA 98007 [208] 885-7e77 OR 454-3743 FAX:1208J B85-7983 Mr. Rich Schipanski July 9, 1991 Page 2 of 2 Therefore, The Orchards project does not discharge to these problem areas and will not affect these areas one way or the other. Please contact me should you have any ques- tions regarding the above or attached. Sincerely, DODDS ENGINEERS, INC. Edgar T. Jones,P.E. Project Engineer ETJ:cyd Enclosure cc: Craig Krueger, Northward Randall Parsons, P.E., City of Renton • ��� l T R F;S w y^A 9 •'� R itl 407 ..._ yY,,r r � TR 6. Y 419 ( � T R �. i 400 L v00 'I I - .. II _ NE. 4T r BANK _ Cl'�1,LVERT "All _ - ,�_ _0 a Ii THE ORCHARDS DOWNSTREAM DRAINAGE BASIN BOUNDARY 1`� Zit DE188008 7/8/91 • _ DODDS ENGINEERS, INC. _ _ C I VI L E INIGIN E ERING S U R V E Y I N G P L A N N I N G June 13, 1991 DEI Project No. 88008 Mr. Rich Schipanski The Ferris Company 10655 N.E. 4th Street Suite 506 Bellevue, WA 98004 Subject: The Orchards Dear Rich: I have reviewed the information you provided to us regarding the response letters and comments from the public hearing for the EIS for the above-referenced project. I have the following comments concerning this information: 1. Department of Ecology letter dated May 30, 1991 to Mr. Donald Erickson: In paragraph one under the heading of water quality, DOE recommends mulching for cleared areas year round. The standard of the industry is to mulch where areas are not protected by other erosion methods or in areas that become problem siltation areas. Construction problems occur when entire sites are mulched, that is no cutting and filling can be effectively accomplished since the mulch is contaminating the cut and fill material, thus making compaction of onsite materials difficult. Erosion control measures will be designed in accordance with the City of Renton standards. Construction plans will be approved by Renton and inspection of construction activity will also be done by Renton. In paragraph six under the same heading, DOE recommends that natural wetlands not be used in lieu of other treatment and pretreatment of runoff is essential. We will be providing pretreatment of runoff through the use of grass lined swales prior to discharge into the natural wetlands in accordance with the City of Renton standards. In paragraph two under the heading of wetlands, DOE states buffers should be left undisturbed. The City of Renton has approved use of the buffer areas for biofiltration which is a compatible use adjacent to the wetlands and will not hamper the buffer's purpose to achieve adequate protection of habitat for the wetlands. 2. Corps of Engineers letter to Donald Erickson dated May 14, 1991: Regarding the fourth paragraph discussing existing downstream flooding 2 miles downstream of the site, additional detention will be provided onsite and existing release rates be reduced. We met with Mr. Randall Parsons, Utility Supervisor for the City of Renton, regarding existing erosion and flooding in the vicinity of the Maplewood Golf Course. 4205 148TH AVE. N.E., SUITE 200-BELLEVUE, WA 9SO07 [2061 ee5-7B77 OR 454-3743 FAX:[206)Se5-7563 , Mr. Rich Schipanski June 13, 1991 Page 2 of 2 The result of our discussion with the city was to reduce the pre-existing 2-year release rate to 50% and reduce the 10-year release rate to the existing 2-year release rate. In addition, storage will be provided for the 100-year storm event. This will result in an increase in detention for that previously calculated in our January 4, 1991 storm drainage study. The increase in storage was determined to be in the range of 175% of that previously calculated. This increase in storage will be compensated for in deeper water depth in the southeast pond, a new pond in the vicinity of wetland 4, and an increase in the size of area devoted to storage in the vicinity of wetland 1. This concept will be consistent with the proposed wetland modifications for preserving more of wetlands 1, 3, and 4. 3. Mary E. Merbach's letter to the Hearing Examiner and her testimony during the hearing on May 14, 1991 (refer to response to Corp of Engineer's letter above). 4. Ray Griffin testimony during the hearing on May 14, 1991 (refer to response to Corp of Engineer's letter above). 5. David Baldwin testimony during the hearing on May 14, 1991. Orchards does not discharge to the drainage basin problems Mr. Baldwin is describing. 6. James Montgomery testimony during the hearing on May 14, 1991. See comments regarding David Baldwin testimony since this involves same basin problems. 7. Betty C. Ventress' letter to Donald Erickson dated May 10, 1991; Ms. Ventress is concerned about a well on her property. Since the proposed project will not be diverting any surface or subsurface waters in this vicinity, we would expect no impacts from the development on her well. In summary, the major alteration to the proposal due to the comments received, will be a reduction in the 2 and 10-year existing release rates onsite thus increasing onsite storm drainage detention requirements. This will reduce existing release rates leaving the property, thus reducing downstream peak flow rates and stream flow velocities. Therefore, the existing flooding and erosion occurring 1 to 2 miles downstream from the property should actually be somewhat improved due to the proposed storm drainage system of the Orchards. However, since the Orchard is such a small part of this basin, such improvements would be difficult to measure. Please contact me if you have any questions regarding the above. Sincerely, DODDS ENGINEERS, INC. gar, . Jo s,P.E. t sneer ETJ:cyd cc: Craig Krueger, Northward CITY OF RENTON MEMORANDUM DATE: January 21, 1991 TO: Mary Lynne Myer FROM: Randall Parsons' STAFF CONTACT: Kim Scattarella SUBJECT: THE ORCHARDS - DOCUMENTED DOWNSTREAM PROBLEMS AND PROPOSED MITIGATIONS The following is a summary of the documented downstream problems on the drainage system from the site of the proposed Orchards project. We feel that this information should be included in the environmental review of the project due to the potential impacts on the site plan. The proponents should either assess, analyze and provide mitigation for significant impacts the proposal will have on these existing problems or those which would result from the proposal. As can be noted from the enclosed map the east fork of Maplewood Creek begins just north of the proposed site and continues to flow southward through Windsor Place. It combines with the west fork from Maplewood Creek and flows under NE 4th in a 48" CMP. Maplewood Creek continues southward through the proposed Bakke Development to Fernwood North Detention Pond and eventually through the Maplewood Golf Course, crossing under SR-169 and outlets to the Cedar River. The are several specific drainage problems located in the immediate vicinity of the proposed site noted in the Maplewood Drainage Basin Study: Location No. (1) The existing cross culvert that conveys runoff under Duvall Avenue NE appears to have limited capacity and should be analyzed to assure that it can accommodate the 100 year design storm event. The impacts on the floodplain upstream of the culvert as the result of this proposal should be addressed. (2) There has been some flooding and scouring from erosion noted at the Windsor Place Culvert, a 30" cross culvert that flows under Bremerton Avenue NE on the eastern border of Windsor Place Apartments. Flooding has been noted in storms of greater than 10 year frequency. (3) There was flooding noted on January 9, 1990, (approximately a 33 year 24 hour duration storm event) that occurred approximately 300' east of the intersection of Duvall and NE 4th. The ditch and drainage system that conveys storm water under NE 4th and southward was over capacity. Mary Lynn Myer Page 2 (4) South of NE 4th the channel that passes through the Bakke Development is restricted. Increased runoff would require drainage improvements along this area as was proposed in the study. These improvements were proposed to include channel reconstruction with new stream side plantings and a maintenance road. (5) There is evidence of significant accelerated channel erosion affecting the stream bank in the steep sections of the canyon portion of the main channel. The analysis indicates the need for measure to reduce the velocity of storm water flows from new development as the existing velocities exceed the cohesive limits for almost all present and future storm flows. These existing problems could likely be further aggravated by increased runoff volume from the proposed project. Proposed mitigation to address the downstream channel erosion could include channel armoring unstable sections of stream bank or detaining and releasing the projects post developed peak runoff rate for the 2 year, 24 hour design storm event at 50% of the pre-developed 2 year peak runoff rate for the 2 year, 24 hour design storm event. Proposed mitigation for downstream flooding/capacity problems could include installing additional conveyance capacity (subject to assessment of no adverse downstream impacts) or detaining and releasing the projects post developed peak runoff rate for the 10 year, 24 hour design storm event at the pre-developed 2 year peak runoff rate for the 2 year, 24 hour design storm event. The runoff for the projects post-developed peak runoff rate for the 100 year design storm event would have to be analyzed to assure compliance with Core Requirement #3 in the King County Surface Water Design Manual. If you have any questions regarding this information or these recommended mitigations, please contact Kim Scattarella at extension 6193. 91-056:RLP:ps CC: Arnie Henninger Attachment 9 y�� . REC t D7/3/, PLPUBUC WORKSV CiZITYOF REN;WN King County Surface Water Management Division Department of Public Works Yesler Building 400 Yesler Way-Room 400 Seattle,WA 98104-2637 (206)296-6519 July 30, 1991d � Ms. Mary E. Merbach, Trustee Maplewood Heights Maintenance Corporation 13732 Southeast 141st Street Renton, WA 98059 RE: Flooding in Puget Colony Dear Ms. Merbach: Thank you for your July 11, 1991 letter concerning the SEPA review of The Orchards proposed development upstream of the Maplewood Heights Maintenance Corporation's greenbelt. In response to your request, I have enclosed a copy of my June 18, 1991 letter to Lynn Guttman of the City of Renton's Department of Public Works regarding possible impacts of this development upon Maplewood Creek's severe erosion problems. Thank you again for your concern in this matter. If our staff can offer any further information to assist you, please call Curt Crawford, Acting Supervising Engineer, Drainage Investigation Unit, at 296-6519. Sincerely,' Jim Kramer Manager JK:RS:vs M21 :LT12 Enclosure cc: Bruce Laing, King County Councilmember ATTN: Wes Phillips, Legislative Aide Tim Hill , King County Executive Lynn Guttman, Director, City of Renton Department of Public Works City of Renton Planning Department City of Renton Building Department Barb Throm, Executive Secretary, Maplewood Heights Maintenance Corporation Paul Tanaka, Director, Department of Public Works ATTN: Ann Kawasaki , Deputy Director Ken Guy, Assistant Manager, Surface Water Management Division Dick Thiel , Manager, Engineering Services Section ATTN: Curt Crawford, Acting Supervising Engineer, Drainage Investigation Unit Randy Snow, Engineer Kink Count• Surfacr 1later )Management Di%'ision Deparunen: Of Public W01'kf 730 Dexter Horton Ruild rii: 710 Seconc Avenm Seattle, Washington 9t'104 (206)396-6585 June 1E, 1991 Mr. Lynn Guttman Department of Public Works City of Renton 200 Mill Avenue South Renton, WA 98055 RE: Drainaae Issues in the Proposed Orchards Plat Dear Mr. Guttman: Please allow me to express the interest and concern of King County Surface Water Management Division staff regarding the proposed plat of The Orchards, near Northeast 4th Street and Duvall Avenue Northeast. I understand the project is in the Final Environmental Impact Statement stage of approval . We are concerned by possible downstream impacts to existing drainage problems, and would like to ensure coordination between our agencies in addressing these problems. There are two specific areas of concern which could be impacted by The Orchards project. One of these areas is the basin draining through the plat of Puget Colony Homes. This area is roughly bounded on the west by 136th Avenue Southeast from Northeast 4th Street (Southeast 128th Street) south to Southeast 132nd Avenue. North of Northeast 4th Street, the basin extends from Duvall Avenue Northeast (138th Avenue Southeast) and Northeast 4th Street northeasterly to about 140th Avenue Southeast and Southeast 124th Street. Although engineers for the The Orchards project and your staff indicate that none or the project will drain to Puget Colony Homes, there is widespread concern among the residents of the plat about the impact of new development. The plat floods frequently due to its extreme flatness and Possibly to partial filling of the wetlands between Southeast 128th and Southeast 132nd Streets. This problem was not mentioned in the October 1989 draft Maplewood Creek Basin Plan prepared for the City of Renton by Parametrix, Inc. We believe that any additional runoff through Puget Colony Homes, or through the wetland to the north, or any filling and clearing of the likely wetland area north of Southeast 128th Street (adjacent to The Orchards) , would adversely impact County and private property in the plat as well as natural resources both upstream and downstream. The second area of concern, which was addressed by the draft Maplewood Creek Basin Plan, is erosion of the natural channels leading to the Maplewood Golf Course. These streams are identified as Tributaries 302 and 303 in the 1967 Mr. Lynn Guttman June 18, 1991 PagE Two King County Basin Reconnaissance Report, and the West and East Forks , respectively, of Maplewood Creek in the Maplewood Creek Basin Plan. Erosion along the western tributary, part of which is within Renton, threatens the road right-of-way at the intersection of Southeast 136th Street and 13Eth Avenue Southeast. Further downstream, below the confluence of the two trib- utaries and upstream of Maplewood Golf Course, a concrete siltation dam was washed out this vear by high flows. A regional retention/detention pond to be built by King County along Tributary 303 below the plat of Puoet Colony Homes was proposed in the draft Maplewood Creek Basin Plan. While this facility would help to attenuate flows in the channel downstream, it would do nothing to help flooding upstream. I think it would be helpful to con- sider alternative courses of action. I hope to coordinate with your staff our review of any future plans , including The Orchards, which would affect the above-mentioned areas of concern. With the initiation of the Lower Cedar River Basin Plan by Surface Water Management Division staff, this may be an appropriate time to address drainage issues in the basin jointly. Sincerely, / A Jim Kramer ` lanaoer JK:RS:ad W19:LT2 cc: Ray Griffin Dave Baldwin Ken Guy, Assistant Manaoer. Surface Water Manaaement Division Curt Crawford, Acting Supervisino_ E^Cineer, Drainage Investigation Unit ATTN: Randv Snow, Engineer CITY OF RENTON MEMORANDUM DATE: April 21, 1992 TO: Bill Stalzer FROM: andall Parsons STAFF CONTACT: Dan Carey SUBJECT: THE ORCHARDS CONCEPTUAL DRAINAGE PLAN APPROVAL The Surface Water Utility has approved the major assumptions (sub-basin delineation, points of discharge, bypass areas), and proposed surface water control facility locations, configurations and preliminary sizing for this proposed master plan. Except for the hydrologic analysis and sizing methodologies,this approval does not preclude revisions necessary to comply with the City's Building Codes in effect at the time the City accepts the completed applications for building and construction plans for the various phases of the development. It should also be noted that the detailed hydrologic and hydraulic calculations are assumed to be correct and have not been verified by the Surface Water Utility. These calculations will be completely reviewed and checked for accuracy as part of the review of the detailed construction plans for the several construction phases of the project. The following are the Surface Water Utility's conditions of approval with regards to this conceptual drainage plan: (1) All surface water facilities needed to mitigate the impacts of any phase of the master plan must be constructed prior to approval of occupancy for any building within a phase contributing runoff to the downstream system. (2) There must be a master home owners/property owners association created which shall be responsible for maintaining, operating, repairing and replacing all of the surface water control facilities outside of City road right-of-way for the project (except as noted in (3) below). There shall be Private Drainage Easements dedicated over all drainage facilities outside of City rights-of-way. All other drainage facilities shall have dedicated Access Easements to the City. (3) The master home owners/property owners association shall also be responsible for maintaining, operating, repairing and replacing the main storm drainage conveyance system in the roadway which conveys runoff from the west side of Duvall Ave. (currently an 18 inch diameter culvert)to the regional wetland/retention/detention facility (Wetland 300) and the main storm drainage conveyance system in the roadway which conveys runoff from the east side of Duvall Ave. (currently a 36 inch diameter culvert)from the regional wetland/retention/detention facility (Wetland 300)to the proposed new bypass storm drainage conveyance system from the north. This bypass system will convey runoff from the proposed Forest Creste wetland/ retention/detention facility (on the east side of Duvall Ave. and north of the proposed extension of N.E. 6th St.) down to the connection with the existing 36 inch culvert and will be maintained, operated, repaired and replaced by the City. Please call me at X-5548 if you have any questions regarding these conditions. RP:rp:ORCHHRG.DOC cc Gregg Zimmerman CITY OF RENTON QF��� CITY OF RENTON ✓(/� cA MEMORANDUM i 0 3 DATE: May 30, 1991 TO: Bill Stalzer, Project Manager FROM: Mary Lynne Myer, Principal Planner SUBJECT: The Orchards Draft Supplemental EIS Our earlier memo of May 30, 1991 inadvertently deleted additional comments on water quality for the DSEIS for the Orchards Project. Please include these comments with our earlier submittal. According to the DSEIS, aquifer recharge will be significantly reduced, due to the increase in impervious surface and vegetation removal, hastening run-off. Our earlier memo suggests ways to alleviate run-off and promote on-site absorption through retention of several wetlands. However, water quality will also be affected under the proposal. With urbanization, phosphates, nitrates, heavy metals, oil and grease will enter the natural water systems. The DSEIS suggests oil water separators and retention/detention ponds . Traditionally good maintenance of these facilities is essential for proper longterm functioning. The DSEIS notes that homeowners associations will provide maintenance. Past municipal and county experience shows less than satisfactory operations when left to such organizations. Rather than homeowner responsibility, a different model should be evaluated. The Final Supplemental EIS should discuss other more reliable, long term alternatives. Thank you for the opportunity to comment. Please do not hesitate to call if you have any questions. cc Kay Shoudy, Planning Manager Donald K. Erickson, Zoning Administrator Randall Parsons, Sewer and Surface Water Utility Manager CITY OF RENTON MEMORANDUM DATE: May 30, 1991 TO: Bill Stalzer, Project Manager FROM: Mary Lynne Myer, Principal Planner STAFF CONTACT: Amanda Azous, Wetlands Consultant SUBJECT: The Orchards Draft Supplemental EIS (DSEIS) The Orchards property was recently inventoried as part of a city-wide effort to inventory critical areas as mandated by the Growth Management Act. While the information in the inventory is still preliminary, it is clear from the data obtained to date, that the wetlands on the Orchards property are some of the few forested wetlands remaining in the City of Renton. Forested wetlands are increasingly rare due to logging and development pressures, and provide unique habitats for species, such as flycatchers or mountain beaver, that require closed canopy forest stands. The wetlands on the Orchards property are particularly valuable, due to their unusual mix of an Oregon Ash overstory with a slough sedge understory. On a recent visit to the site, it appeared that the wetlands may not be accurately delineated. Standing water was found outside markers that appear to be the delineation of the wetland edge. Based on the flagging observed in the field, Wetland No. 2 and perhaps others may be larger than what is currently delineated. Other areas of standing water and wetland plants, not shown on the wetland plan were observed near the western edge of the property. It is possible that these were off site since the property line location was not clearly identifiable, but the possibility that other wetlands exist on site should be investigated. Hydrologically these wetlands provide critical upland storage. Upland wetlands are very important for de-synchronizing floodwaters. Without storage in upland areas, floodwaters tend to build up on themselves resulting in cumulatively greater problems downstream. The city is particularly concerned about potential flooding problems resulting from this project especially given past flood damage that has occurred in the 4th Street Corridor and areas near the Cedar River. There are some indications that the wetlands on the Orchards property are part of the headwaters of Maplewood Creek. Wetland No. 1 has some velocity, and appears, from aerial photos, to become Maplewood Creek downstream. In addition, another stream was located flowing from off-site into what appeared to be Wetland No. 3. These data suggest that the Orchard's wetlands are part of a larger hydrologic system. King County regulations have become a standard for wetland management in this area. Regulations disallow the use of Class 2 wetlands for stormwater management unless the project is necessary for public health, safety and welfare or unless the project is intended to repair downstream resources, neither of which is the case for this project. As such, Wetlands No. 3 and 7 should not be altered. Wetland No 1 should also not be altered since it is clearly hydrologically connected to offsite drainages and is likely part of Maplewood Creek's headwaters. We strongly recommend the project plan be revised to consider exploiting the existing drainage patterns and retaining as much of the existing wetland areas as possible. Wetlands 1, 3 and 7 should be maintained as they exist and should be protected by a minimum of 50 feet of natural vegetation as a buffer. The remaining Class 3 wetlands could be altered for stormwater management or filled and mitigated for on the site. Acceptable mitigation is not provided by terracing and deepening a wetland as suggested in the DSEIS. Mitigation must be in the form of restored or created wetland areas or through habitat enhancement activities. Mitigation ratios recommended by the Department of Ecology are 3:1 for forested wetlands, 2:1 for scrub-shrub and 1.5:1 for emergent marsh wetlands. The application of the ratios will depend on what, if any wetlands are filled on the project site. The response to the DSEIS by the Army Corps of Engineers indicates that project alternatives should be considered which minimize impacts to the wetlands. (Letter dated May 14, 1991). They note that the Section 404b permit application must show practicable alternatives that are the least environmentally damaging to the wetlands. We encourage project development alternatives which increase hydrologic connectivity among the wetland systems on site and increase the connectivity of natural habitat areas. For example, a more acceptable approach would be to design the project so that wetlands 3, 4 and 8 were hydrologically connected. This could be accomplished with some combination of created wetlands needed for stormwater management and biofiltration swales. These areas could also provide valuable habitat connections with the remaining wetlands for wildlife use. An integrated connected system could provide the required water storage, retain much of the existing high quality habitat area and result in a valuable amenity for the development project. Buffer averaging could be used to facilitate creating connections between habitat areas and to reduce extraordinary hardships caused by circumstances peculiar to the property. However, the buffer should be no less than 25 feet at any point and should be left as undisturbed vegetation. Buffer widths could be averaged over the site as long as the total area contained within the buffer is no less than that contained within the standard buffer prior to averaging. Although we have provided extensive comments on the DSEIS, we believe the project has many attributes and should continue to completion. We are available to meet with Surface Water staff and you to discuss these issues further. We are committed to finding solutions which meet the goals of the proponent and the city. I can be reached at 235-2552. cc: Kay Shoudy, Planning Manager Donald K. Erickson, Zoning Administrator /Randall Parsons, Sewer and Surface Water Utility Manager CITY OF RENTON MEMORANDUM DATE: May 24th, 1991 TO: Mary Lynne Myer FROM: Randall Parsons SUBJECT: The Orchards FEIS I understand that it has been determined that the large wetlands area currently shown to be dredged and used for the storm water management facilities for this project will not be allowed. This will require that storm water management facilities be provided by excavating areas currently shown on the site plans for development. In addition,the water quality management facilities required to treat the runoff prior to discharge to these wetlands will require additional area currently proposed for development. I strongly recommend that the development plans be revised and a conceptual drainage plan and analysis be prepared(as is required by Site Plan Approval,per City Code Section 4-22-5)prior to finalizing the EIS. This is based on this significant new information and due to the large amount of storage volume required to provide the storm water control needed in order to prevent aggravation of the existing significant downstream drainage problems that we and the King County Surface Water Management Division have documented. I would propose that it is likely that the required design revisions may be of sufficient magnitude that a new DEIS may be warranted. The EIS would clearly be materially deficient without these revisions and the conceptual drainage plan and analysis performed for the actual project design that is feasible. Please call me at extension SS48 if you have any questions. RP:rp CITY OF RENTON MEMORANDUM DATE: May 24th, 1991 TO: Mary Lynne Myer FROM: Randall Parsons SUBJECT: The Orchards FEIS I understand that it has been determined that the large wetlands area currently shown to be dredged and used for the storm water management facilities for this project will not be allowed. This will require that storm water management facilities be provided by excavating areas currently shown on the site plans for development. In addition,the water quality management facilities required to treat the runoff prior to discharge to these wetlands will require additional area currently proposed for development. I strongly recommend that the development plans be revised and a conceptual drainage plan and analysis be prepared (as is required by Site Plan Approval, per City Code Section 4-22-5)prior to finalizing the EIS. This is based on this significant new information and due to the large amount of storage volume required to provide the storm water control needed in order to prevent aggravation of the existing significant downstream drainage problems that we and the King County Surface Water Management Division have documented. I would propose that it is likely that the required design revisions may be of sufficient magnitude that a new DEIS may be warranted. The EIS would clearly be materially deficient without these revisions and the conceptual drainage plan and analysis performed for the actual project design that is feasible. Please call me at extension 5548 if you have any questions. RP:rp - ',�lii►7�-� �"� I �/ ,, �-:� fig toll �'- ��1� • �7 FIR i • � •. -AM Oil v9� � ��. � � ���� � �� a �:=_- � �;� � �. f� ,. � ► f •• - / WOW �� CITY OF RENTON Public Works Department Earl Clymer, Mayor Lynn Guttmann,Director June 12, 1990 Craig Krueger NORTHWARD 1560 - 140th Avenue N.E., Suite 100 Bellevue, WA 98005 Subject: The Orchards Craig, I have reviewed the latest copy of the "Preliminary Design Report for a Sanitary Sewer Interbasin Transfer from the Upper Heather Downs Basin to the Lower Maplewood Basin" and find only very minor changes are needed. Following is an outline of the steps necessary to move this project along: 1) As per our June 11 telephone conversation with Ed Jones, the following changes should be made to the report: A) In the second paragraph of the summary, change Maplewood Heights Interceptor to East Renton Interceptor. B) Add a North arrow to Figure 2-A. C) Call out size of new pipe in Figure 7. D) The installation of the new 24" sewer main between MH's 18-3 and 18-1 is in Zone 1 of the Aquifer Protection Area and thus will have to be ductile iron with a polysleeve to prevent leakage at the joints. 2) Northward needs to request, in writing, an exemption from the Moratorium and conceptual approval of the proposed interim improvements outlined in the above- mentioned report. This request should be addressed to the Mayor and City Countil and would need to be received by the City Clerk before 10:00 A.M. on the Tuesday prior to the Monday Council Meeting. From Council, it will be referred to the Utilities Committee (second and fourth Tuesdays of the month). At Committee, Northward/Dodds will be given an opportunity to make the proposal. The Public Works Department will make a recommendation to the Committee, who will then make a recommendation of concurrence or non-concurrence to the full Council. 3) Provide verification that Forest Crest has been given the opportunity to participate in the interim improvements and their response. This needs to be provided to the City at the earliest convenience. 200 Mill Avenue South - Renton, Washington 98055 - (206) 235-2631 f Craig Krueger June 12, 1990 Page Two The lack of this verification may have a negative impact on the recommendation by either Public Works Department staff or the Utilities Committee. Similarly, a negative response by Forest Crest may have an impact on their possibility of exemption and the City may want to contact and confirm their response prior to making a recommendation on your project. If you have any questions, please contact me at 277-6206. Very truly yours, Michael A. Benoit Wastewater Utility KRUEGER/MABif cc: Jim Olsen, Dodds Engineers Richard Anderson, Utility Systems Manager Randall Parsons, Wastewater Supervisor Rick Harbert, RH2 Engineering Mary Lynne Myer, Planning Division C r rY OF RENTON RECEIVED CITY OF RENTON FEB - 6 1991 DEVELOPMENT SERVICES MEMORANDUM DIVISION DATE: February 5, 1991 TO: Mary Lynne Myer, Senior Environmental Planner FROM: David M. Christenseif, Wastewater Utility Engineer SUBJECT: Developmental Review of The Orchards Revisions This memo is a follow-up to this Section's comments on the EIS portion of the project dated November 15, 1990. The previous memo addressed specifically the issues related to the EIS. This memo shall cover exclusively Wastewater concerns for the proposed development. The concerns are as follows: ■ The proposed sewer located off-site from N.E. 7th Pl. to N.E. 7th Ct. shall be rerouted across the proposed detention pond to the easterly portion on N.E. 7th Pl. The sanitary sewer manholes shall be located within the detention pond access road area in order to facilitate the City's ability to maintain this line ■ Applicant shall install a 12" sewer main within Duvall Ave. N.E. from N.E. 8th St. to N.E. 4th St. This sewer is included within the City's 1983 Comprehensive Plan, as well as the 1991 update scheduled for adoption in June of 1991. The design shall be coordinated with the City of Renton's East Renton Interceptor Project to insure that inverts can be matched. Ultimately "Phase G" shall be routed to this 12" sewer main. However, since the 12" sewer main will be a dry sewer until completion of the City's East Renton Interceptor Project, the applicant may temporarily route "Phase G" through the line proposed in Anacortes Ave. N.E. The design shall incorporate a method to reroute the sewage to the 12" line in Duvall Ave. N.E. upon completion of the East Renton Interceptor Project. The method shall not require excavation within Duvall Ave. N.E. right-of-way. ■ Applicant shall install an 8" and/or 12" sewer main (size dependent upon Hydraulic Analysis) along N.E. 8th St. from Anacortes Ave. N.E. to the northwesterly boundary of the proposed development. This sewer is part of the City's proposed Honeydew Interceptor that is included in the update of the Sewer Comp Plan. ■ The applicant's proposed "Phase D" shows a sewer main within N.E. 6th St. running to the western boundary of the proposed development. It does not indicate where it is to tie in to the City system and our records do not indicate any sewer to be available at this location. F .M Mary Lynne Mver February 5, 1991 Page Two ■ The applicant shall submit Hydraulic Analysis for this project on the Anacortes Ave. N.E. line. The analysis shall be for two conditions: The first condition shall be for the proposed development including any portions that ultimately will be directed to the new 12" sewer main constructed in Duvall Ave. N.E. The second condition shall include that portion of this development that ultimately only flows into the line on Anacortes Ave. N.E. as well as the peak developed flow of the proposed Honeydew Interceptor and the anticipated developed flow from the northerly parcels which will be served by the extension of the sewer main located within Anacortes Ave. N.E. If either analysis identifies capacity problems within the existing sewer main in Anacortes Ave. N.E., it shall be the responsibility of the applicant to upsize the line accordingly. If you have any questions, please contact me at Ext. 6212. ORCHARDS/DMC:lf cc: Randall Parsons a PLANNING DNISION Of fY OF R INI-019 CITY OF RENTON ,BAN 2 5 1991 MEMORANDUM nk--LA' V ED DATE: January 25, 1991 TO: Don Erickson Gregg Zimmerman FROM: Randall Parsons SUBJECT: STORM AND SURFA E WATER DRAINAGE CORE REQUIREMENT#2 OFF-SITE ANALYSIS Following discussions I had with Mary Lynne on the Orchards EIS, we felt it would be useful to reiterate a very important aspect of the King County Surface Water Design Manual requirements that were adopted and incorporated into our Chapter 22: Storm and Surface Water Drainage Code last June (see enclosure). This requirement states that projects/approvals that will have impacts on drainage have a Level 1 off-site analysis prepared by a registered professional civil engineer and submitted with the initial permit application. The parameters for this analysis are described in the enclosed excerpt from the manual. In administering this requirement, many agencies, including the King County Building and Land Development (BALD) Division, require this analysis to be submitted with the SEPA Checklist. There are a lot of good reasons for doing this. The main reasons are: (1) that it is felt that an applicant cannot truthfully respond to Section B. ENVIRONMENTAL ELEMENTS: 3. WATER without performing most of the activities required by this Level 1 analysis (this information can often be critical to deciding on the threshold determination of a proposal); and, (2) there are often off-site drainage conditions, both upstream and downstream, which have a direct bearing on the proposed uses and site plan configurations for a particular project. I am, therefore, strongly recommending that you consider enforcing this requirement. I believe that the long term result will be much better accuracy in evaluating threshold determinations and fewer potentially significant revisions to applicant's site plans at the construction plan/permit stage following the SEPA process. Give me a call at 5548 if you have any question regarding the application of this requirement. On a related manner, I concur with the EIS review process described in your memo of January 24, 1991. I have routed this memo to my staff and noted that they should charge their time to the permit review project work order number for the specific projects. 91-066:RP:ps CC: Mary Lynne Myer Kim Scattarella Enclosures (f \y 4 P t I G DIVISiCOi'f CITY OF RENTON CrryOF RENT,-)?,, MEMORANDUM DATE: January 21, 1991 TO: Mary Lynne Myer FROM: Randall Parsons , STAFF CONTACT: Kim Scattarella SUBJECT: THE ORCHARDS - DOCUMENTED DOWNSTREAM PROBLEMS AND PROPOSED MITIGATIONS The following is a summary of the documented downstream problems on the drainage system from the site of the proposed Orchards project. We feel that this information should be included in the environmental review of the project due to the potential impacts on the site plan. The proponents should either assess, analyze and provide mitigation for significant impacts the proposal will have on these existing problems or those which would result from the proposal. As can be noted from the enclosed map the east fork of Maplewood Creek begins just north of the proposed site and continues to flow southward through Windsor Place. It combines with the west fork from Maplewood Creek and flows under NE 4th in a 48" CMP. Maplewood Creek continues southward through the proposed Bakke Development to Fernwood North Detention Pond and eventually through the Maplewood Golf Course, crossing under SR-169 and outlets to the Cedar River. The are several specific drainage problems located in the immediate vicinity of the proposed site noted in the Maplewood Drainage Basin Study: Location No. (1) The existing cross culvert that conveys runoff under Duvall Avenue NE appears to have limited capacity and should be analyzed to assure that it can accommodate the 100 year design storm event. The impacts on the floodplain upstream of the culvert as the result of this proposal should be addressed. _(2) There has been some flooding and scouring from erosion noted at the Windsor Place Culvert, a 30" cross culvert that flows under Bremerton Avenue NE on the eastern border of Windsor Place Apartments. Flooding has been noted in storms of greater than 10 year frequency. (3) There was flooding noted on January 9, 1990, (approximately a 33 year 24 hour duration storm event) that occurred approximately 300' east of the intersection of Duvall and NE 4th. The ditch and drainage system that conveys storm water under NE 4th and southward was over capacity. i Mary Lynn Myer Page 2 r' (4) South of NE 4th the channel that passes through the Bakke Development is restricted. Increased runoff would require drainage improvements along this area as was proposed in the study. These improvements were proposed to include channel reconstruction with new stream side plantings and a maintenance road. (5) There is evidence of significant accelerated channel erosion affecting the stream bank in the steep sections of the canyon portion of the main channel. The analysis indicates the need for measure to reduce the velocity of storm water flows from new development as the existing velocities exceed the cohesive limits for almost all present and future storm flows. These existing problems could likely be further aggravated by increased runoff volume from the proposed project. Proposed mitigation to address the downstream channel erosion could include channel armoring unstable sections of stream bank or detaining and releasing the projects post developed peak runoff rate for the 2 year, 24 hour design storm event at 50% of the pre-developed 2 year peak runoff rate for the 2 year, 24 hour design storm event. Proposed mitigation for downstream flooding/capacity problems could include installing additional conveyance capacity (subject to assessment of no adverse downstream impacts) or detaining and releasing the projects post developed peak runoff rate for the 10 year, 24 hour design storm event at the pre-developed 2 year peak runoff rate for the 2 year, 24 hour design storm event. The runoff for the projects post-developed peak runoff rate for the 100 year design storm event would have to be analyzed to assure compliance with Core Requirement #3 in the King County Surface Water Design Manual. If you have any questions regarding this information or these recommended mitigations, please contact Kim Scattarella at extension 6193. 91-056:RLP:ps CC: Arnie Henninger Attachment DEPARTMENT OF PLANNING/BUILDING/PU136,;WORKS ENVIRONMENTAL CHECKLIST REVIEW SHEET REVIEWING DEPARTMENT: NOV 3&xzr 930' fi DATE CIRCULATED: Nov 2, 1990 COMMENTS DUE: Nov,14, 1990I + ECF-138-90 R,PP,SA APPLICATION NO(S): PROPONENT: Northward Inc. PROJECT TITLE: The Orchards BRIEF DESCRIPTION OF PROJECT 275 apartment units,68 townhouse units, 121 single family lots,and 28,000 sq.ft.of office/commercial space on 62.3 acre site. LOCATION:northeast protion of City,primarily southwest of the Intersection of Duvall Avenue NE and NE 8th Street,if extended. SITE AREA: 62.3 acre site BUILDING AREA(gross): IMPACT REVIEW ON ENVIRONMENTAL ELEMENTS: PROBABLE PROBABLE MORE MINOR MAJOR INFORMATION IMPACT IMPACT NECESSARY 1. Earth 2. Air _ 3. Water 4. Plants 5. Animals 6. Energy&Natural Resources 7. Environmental Health 8. Land&Shoreline Use 9. Housing 10. Aesthetics 11. Light&Glare 12. Recreation 13. Historic&Cultural Preservation 14. Transportation 15. Public Services 16. Utilities COMMENTS: SEE 4rIAeOED . We have reviewed this application with particular attention to those areas In which we have expertise and have identified areas of probable Impactor areas where additional Information is needed to properly assess this proposal. Signature of Director or Authorized Representative Date eirvrvslil t Viet N N 1 CITY OF RENTON ; :3 11gp MEMORANDUM DATE: November 9, 1990 TO: Mary Lynne Meyer, Senior Planner, Current Planning FROM: Randall Parsons, P.E., Utility Superviso Storm water/Waste water Utility Sectio STAFF CONTACT Kim Scattarella, E.I.T., Engineer, Storm water Utilit Section SUBJECT: ENVIRONMENTAL REVIEW COMMENTS - THE ORCHARDS After review of the Preliminary Supplemental Draft EIS for the Orchards, I have the following comments: - On page 1-3, reference is made to the Aquifer Protection Ordinance for Aquifer Protection Zone 2. The APO has not yet been adopted, so the change in wordage will be needed there. More specific references as to how stormwater will be addressed in regard to the APO are also requested. _On page 3-3, the last sentence in paragraph 2 under Surface Water shall be changed to read, "On-site drainage facilities have been designed to accommodate a 100-year/7- day storm event for developed conditions with a 100-year/7-day predeveloped release rate". The original 25 ear design storm for developed conditions storage/2-year cya,e��•"s release for predeveloped a +erk can not apply, since this is a closed depression, and the above requirements are in compliance with the King County Surface Water Design Manual. - An acceptable Temporary Erosion/Sedimentation Control Plan shall be required that is in compliance with the 1990 King County Surface Water Design Manual. - On page 3-6, in paragraph 1,under Wetlands, the compliance with the current draft of the Aquifer Protection Ordinance shall be mentioned. - On page 3-8, under mitigating measures it shall changed to read " Should construction take place between November and March, more extensive erosion control measures would be required, such as: covering of exposed soils and filtration of turbid waters per City of Renton Erosion Control requirements, and the King County Surface Water Design Manual". - On the same page, under stormwater drainage facility design, it shall read "designed to meet the City of Renton standards to detain a 100-year/7-day design storm event for developed conditions with a 100-year/7-day pre-developed release rate." This site i i I t We have reviewed this application with particular attention io those areas In which we have expertise and have identified areas of probable Impact or areas where additional Information is needed to properly assess this proposal. i Signature of Director or Authorized Representative Date envmhl F. is presumed to be a closed depression, unless otherwise proven by the engineer, so this detention requirement will apply, and the 25-year storage/ 2-year released rate per original comments will not apply. The method used to determine the flows shall be in compliance with the new King County Surface Water Design Manual. - On page 3-14, wetlands buffer is given as 25 feet. However, normally the required minimum buffer is dependent upon the wetlands classification, based on DOE criteria. The wetlands classification of the seven wetlands on-site shall be determined, and from that the minimum buffer width can be determined from DOE criteria(since the City does not currently have its own wetlands ordinance). - A soils report by a Licensed Geotechnical Engineer with percolation test results (per format in the King County Surface Water Design Manual) shall be submitted to the City of Renton, and the data used in the retention/detention storage calculations, utilizing the 100 year/7-day design storm. Other comments from the previous Environmental review memo dated May 4, 1990 continue to apply. Attachment I i' We have reviewed this application with particular attention fo those areas In which we have expertise and have identified areas of probable impact or areas where additional information Is needed to properly assess this proposal. Signature of Director or Authorized Representative ! I� Date GiVMII M E M O R AND "a DATE: May 4, 1990 - ?• :_' TO: Lenora Blauman, Senior Planner FROM: Kim Scattarella, Stormwater Engineering Specialist SUBJECT: ENVIRONMENTAL REVIEW COMMENTS— THE ORCHARDS After review of the Northward Rezone and Development (also known as The Orchards), I have the following comments : - Provide a 22" X 34" Mylar showing the Existing and Design for the Storm Drainage (i.e. Conveyance Pipes, CB's and Manholes). Provide the rim and invert elevations, pipe length, material, and slope. - Show all existing and future storm easements. - The site is a closed depression. Therefore, the detention requirements shall be a 100 year/7-day design storage, as computed by the SCS or Santa Barbara Hydrograph method (per 1990 King County Surface Water Design Manual). No natural outlet is shown for this site. - A soils report, by a Licensed Soils Engineer, with percolation test results shall be submitted to Public Works, and the data used in the retention/ detention storage calculations. - Erosion and Sedimentation Control plans shall be implemented both before and during construction, and remain in place until all construction is completed. - All stormwater draining onto the wetlands shall be mitigated by a flow restrictor manhole, followed by a Baffled Oil/Water separator prior to entering the depression area that has been designated as a wetlands. cc: Gregg Zimmerman, Plan Review We have reviewed this application with particular attention to those areas in which we have expertise and have identified areas of probable impact or areas where additional information is needed to properly assess this proposal. We have reviewed this application with particular attention to those areas In which we have expertise and have identified areas of probable Impactor areas where additional Information Is needed to properly assess this proposal. Signature of Director or Authorized Representative c(� Date envrvshl v DEPARTMENT OF PLANNING/BUILDING/PUBLIC WORKS PRELIMINARY REPORT TO THE HEARING EXAMINER PUBLIC HEARING APPLICANT: Northward Properties PROJECT NAME: The Orchards FILE NUMBER: ECF, R, SA, PP 138-90 LOCATION: To the north of the intersection of Duvall Avenue, N.E. and N.E. 4th Street extending from approximately N.E. 5th Street to N.E. 8th Street along the west side of Duvall Avenue, N.E. with a small parcel connecting to Union Avenue, N.E. at N.E. 7th Street and a larger parcel along the east side of Duvall Avenue, N.E. from approximately N.E. 5th Street to N.E. 6th Street. A. SUMMARY AND PURPOSE OF REQUEST: The applicant seeks: 1) The rezone of 3.46 acres from G-1, General Zone to R-1, Residential Zone (Parcel A); 2) The rezone of 28.14 acres from R-1, Residential Zone, R-2, Residential Zone to R-1, Residential Zone (Parcel B); [Parcel B also includes small portions of G-1, General Zone and R-3, Residence District.] 3) The contract rezone of approximately 9.05 acres from R-2, Residential Zone and R-3, Residence District to R-3, Residential Zone (Parcel C); 4) The contract rezone of approximately 3.21 acres of G-1 , General Zone to R-3, Residence District (Parcel D); 5) The contract rezone of approximately 7.04 acres of G-1 , General Zone to R-3, Residence District (Parcel E); 6) The contract rezone of approximately 2.21 acres from G-1, General Zone to B-1 , Business District (Parcel F);and 7) The contract rezone of approximately 9.17 acres of G-1, General Zone to R-3, Residence District (Parcel G); 8) Site plan approval for a community of 119 single family residences, 63 townhouses, 276 multi- family units, two recreation facilities of approximately 3,500 square feet each, one recreation facility of approximately 900 square feet, approximately 28,000 square feet of office and commercial space in 3 buildings, and related open spaces, detention facilities, and parking spaces; and 9) Preliminary plat approval for 119 single family lots, infrastructure improvements, and wetland enhancements. B. GENERAL INFORMATION: 1 . Owner of Record: Northward Properties 2. Applicant: Northward Properties pret—pt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARD. April 21, 1992 Page 4. Existing Zoning in the Area: R-1, R-2, R-3, G-1, and B-1. 5. Comprehensive Land Use Plan: Single Family; Low Density Multifamily; Medium Density Multifamily; and Office/Office Park. 6. Size of Property: 62.3 acres 7. Access: Duvall Avenue, N.E., Union Avenue, N.E., and N.E. 8th Street 8. Land Use: Vacant except for 2 single family houses. 9. Neighborhood Characteristics: North: Elementary School leased to Renton Technical School, playfields, vacant land and single family residences. East: Primarily single family residences; some vacant land. South: Primarily multifamily, commercial and office uses, with some single family residences. West: Primarily single family uses; some multifamily uses. C. HISTORICAL/BACKGROUND: Action File Ordinance Date Initial annexation --- 3553 June, 1981 Final EIS for rezone and February, 1983 development proposal Portions rezoned to R-1, --- 3795 October, 1983 R-2. and R-3 (with PUD condition) Resolution 2764 July, 1989 establishing sewer moratorium and granting limited exemptions Development application and rezone requests October, 1990 Final EIS issued ECF 138-90 --- August, 1991 Mitigation Document issuedECF 138-90 --- December, 1991 Resolution 2880 February,1992 substituting site plan review for PUD approval prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS Page 3 April 21, 1992 D. PUBLIC SERVICES: 1. Utilities a, Water: The project site is in the City of Renton Water Service Area. Water lines do not exist on the site, with the closest mains located in Union Avenue to the west and in the Windsor Place Apartments complex immediately to the southwest of the site. The applicant will provide water main extensions to the site as well as water lines internal to the project. b. Sewer: The project site is within the City of Renton service area. Currently there is a moratorium on sewer extensions to the existing Heather Downs system, which would serve the project; however, The Orchards is one of a list of projects granted a limited exemption from the moratorium by Resolution 2764. It also has been granted approval for an inter- basin transfer if the terms of the moratorium exemption cannot be met. C. Storm Water Drainage: Currently storm water drainage consists of overland flows through seasonal wetlands and ditches on portions of the site. All storm water drainage flows in a southwesterly direction toward Union Avenue and N.E. 4th Street. Culverts provide transport of flows under Duvall Avenue. The storm water drainage system for the project has been designed to provide better management of storm water drainage while protecting the integrity of important natural features. 2. •Fire Protection: Provided by the City of Renton as per ordinance requirements. 3. Transit: The closest service is provided by Metro routes 111 and 147 on N.E. 4th Street. Future service is planned for Duvall Avenue, N.E. 4. Schools: Students living in the project area will attend the following schools: Elementary School: Maplewood Heights is approximately 1/2 mile southeast of the site. Middle School: McKnight Middle School is approximately 1 mile northwest of the site. High School: Hazen High School is approximately 1/2 mile northeast of the site. 5. Recreation: The playfields adjacent to Honeydew Elementary School (the buildings are presently leased to Renton Technical School) are located across N.E. 8th Street. Kiwanis Park is located across Union Avenue at N.E. 8th Street. Other recreational facilities within a 3 mile radius include Windsor Hills Neighborhood Park, Highlands Neighborhood Park and Community Center, Liberty Community Park, Cedar River Community Park, Gene Coulon Memorial Beach Park, and Maplewood Golf Course. E. APPLICABLE SECTIONS OF THE ZONING CODE: 1. Section 4-31-4, G-1 General Zone. 2. Section 4-31-5, R-1, Residential Zone. 3. Section 4-31-7, R-2, Residential Zone. 4. Section 4-31-8A, R-3, Residence District. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 4 5. Section 4-31-10, B-1, Business District. 6. Section 4-31-33, Site Plan Review. 7. Section 4-31-34, Landscaping F. APPLICABLE SECTIONS OF THE COMPREHENSIVE PLAN OR OTHER OFFICIAL CITY DOCUMENT: 1. Environmental Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 8-1 1) 2. Urban Design Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 11-14) 3. Residential Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 14-16) 4. Commercial Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 16-18) 5. Transportation Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 19-22) 6. Utilities Goal, City of Renton Comprehensive Plan Compendium, March 1986 (pages 22-24) 7. Northeast Renton Plan, City of Renton Comprehensive Plan Compendium, 1986 (pp. 55-60). 8. Section 4-8-14 (C), Change of Zone Classification (Rezone), City of Renton Code. 9. Section 4-9, Land Clearing and Tree Cutting Ordinance, City of Renton Code. 10. Section 4-14, Parking and Loading Ordinance, City of Renton Code. 11. Section 9-12, Subdivision Ordinance, City of Renton Code. G. DEPARTMENT ANALYSIS: 1 . BACKGROUND Northward Properties has requested rezones for approximately 57 acres of a 62.3 acre site, site plan approval, and preliminary plat approval for 119 single family lots to permit construction of the first phase of a mixed-use project consisting of 119 single family residences, 63 townhouses, 276 multifamily dwelling units, and approximately 28,000 square feet of office and related commercial space. The Orchards mixed-use project has undergone review since the original rezone application was filed in the early 1980's. The development proposal contemplated in the approved rezone contained 700-750 multifamily dwelling units and 395,000 square feet of office and commercial space. Under the approved zoning, a maximum residential density of 20.8 DU/AC was permitted. The absence of sanitary sewers prevented the project from proceeding at that time. Since 1983, the applicant has held innumerable discussions with various City staff regarding different development configurations for the property. The current proposal reflects the result of over 1 and 1/2 years of discussions, culminating in the submittal of the necessary applications in October of 1990. The average residential density of the current revised proposal is 7.6 DU/AC. prel—pt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 5 Although an EIS was issued in 1983, a Supplemental EIS for the revised, lower density application was initiated in late 1990. The Draft Supplemental EIS was published in April of 1991 and the Final Supplemental EIS was published in August of 1991 . A Mitigation Document was issued by the Environmental Review Committee on December 2, 1991. The current proposal for The Orchards mixed-use project consists of 119 single family residences containing two to four bedrooms each; 63 one and two bedroom townhouses; 276 one, two and three bedroom apartment units; recreational facilities (including 3 buildings), open and covered parking areas, and service areas all totalling 22.99 acres. The townhouse and apartment units will be housed in 45 separate two and three story buildings and overall contain an estimated mix of 69 one-bedroom units, 200 two-bedroom units, and 70 three-bedroom units. Building construction is planned to include bevelled siding, aluminum frame windows, and asphalt shingled roofing. Wetlands, landscape areas, and other open space total 37.1 acres. The office/commercial area is proposed to consist of 3 two-story buildings totalling approximately 28,000 square feet. With outdoor parking areas, they will cover 2.21 acres. Site plan review for the proposed development is required under Section 4-31-33 of the Zoning Ordinance and preliminary plat approval is required under Section 9-12 of the City of Renton Code (Subdivision Ordinance). 2. Pursuant to the City of Renton's Environmental Ordinance and SEPA (RCW 43.21[C], 1971, as amended), the City of Renton Environmental Review Committee on December 2, 1991 issued a Mitigation Document which is attached with this report. 3. Representatives of the various City departments have reviewed the application materials to identify and address land use impacts anticipated from the proposed developments. Comments have been attached and the content has been integrated into the text of this report. 4. REZONE CRITERIA - Section 4-8-14(C)(1) lists three criteria that the Hearing Examiner is asked to consider, along with all other relevant information, in making a decision on a rezone application: a. That substantial evidence was presented demonstrating the subject reclassification appears not to have been specifically considered at the time of the last area land use analysis and area zoning. When this area was annexed to the City in 1981 as part of the Cascadia Annexation, it was given a zoning designation of G-1 consistent with the land use patterns in the immediate area at the time. A rezone application was filed in 1982 for 35.9 acres of the present site; it was approved in 1983 and resulted in the present R-1, R-2, and R-3 zoning designations. Neither the current G-1 parcel abutting Union Avenue nor the G-1 parcels south of N.E. 8th Street were considered as a part of that rezone request. The zoning on these parcels preceded the 1981 Northeast Renton Comprehensive Plan. The proposed zoning reclassifications were not specifically considered as a part of the 1982 rezone request nor have they been considered since. b. That the property is potentially classified for the proposed zone being requested pursuant to the policies set forth in the Comprehensive Plan and conditions have been met which would indicate the change is appropriate. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page c The proposed reclassifications for residential and office/commercial development conform tc the Comprehensive Plan Map designations for single family (6-8 DU/AC), low density multi- family (6-15 DU/AC), medium density multi-family (12-30 DU/AC), and office/office pare uses. These actions also are consistent with Comprehensive Plan Goals, Policies, and Objectives for residential and commercial development and for residential development in areas containing environmentally sensitive features. Residential and commercia' development as proposed are also generally consistent with the Comprehensive Plan for Northeast Renton. Examples of Plan goals, policies, and objectives achieved through the proposed rezones and development are: (1) ENVIRONMENTAL GOAL: To establish and maintain a harmonious relationship between the developed community and its natural environment. (i) BALANCED DEVELOPMENT OBJECTIVE: In order to maintain an acceptable quality of life, land use decisions should be based upon a balance of public services, economic feasibility and environmental considerations. (2) Urban development should be permitted when it is compatible with the natural and human environment. The proposed development has been designed to accommodate residents in a way that will also protect wetland areas. Additionally, the scale and mix of uses in the development are compatible with the surrounding area. (3) Urban development should compensate for the services that it requires. The applicant is constructing the necessary infrastructure improvements at no cost to the City and will also compensate the City through mitigation fees for other services required for the project which have not been compensated for through other means. OPEN SPACE OBJECTIVE: Open space should be obtained and retained in selected areas. (2) Natural vegetation, ravines, slopes, and waterbodies should be preserved to retain open space. The applicant is preserving and enhancing two large wetlands and two smaller wetlands on the site, including buffer areas. VEGETATION OBJECTIVE: To preserve scenic beauty, prevent erosion, protect agains- floods and landslides, minimize air pollution, and reduce storm drainage system costs. (2) In unique and/or fragile areas, desirable natural vegetation should be retained or enhanced. (3) Healthy trees should be retained where possible. The applicant is proposing to retain many of the largest trees on the site, to enhance the vegetation around existing and expanded wetland areas, and to provide compatible landscape elements throughout the site. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 7 SURFACE DRAINAGE OBJECTIVE: To remove harmful materials and sediments, replenish ground water resources, and minimize erosion and floods, surface drainage should be controlled. (1) Storm waters should be retained on-site and then released at a natural rate and quality. The City's storm drainage system should be designed to incorporate natural drainage features. The storm water management system for the project incorporates the wetlands into the overall design. These have been supplemented with drainage and biofiltration swales planted with appropriate vegetation. WATERBODIES OBJECTIVE: To minimize flood damage, minimize the need for storm drainage facilities, promote recreational opportunities, protect wildlife habitats, and enhance adjacent uses, natural waterbodies should be preserved. (3) Development should be designed and constructed to incorporate features of waterbodies. (5) Selected marshes, bogs, and swamps should be preserved and enhanced. Important wetland areas have been preserved and enhanced, and along with biofiltration and drainage swales, incorporated into the overall project design as natural amenities as well as functional storm water management elements. They will be enhanced with appropriate vegetation so they serve as visual amenities, and they will remain accessible to residents via pathways in selected buffer areas. (iii) URBAN DESIGN GOAL: To promote aesthetic and functional harmony, and to provide a proper balance of residential, commercial and industrial areas. LAND DEVELOPMENT OBJECTIVE: Growth and DEVELOPMENT should occur in a timely and logical progression of the existing urban area to maximize the use of existing services. Development has occurred steadily over the last ten years eastward along N.E. 4th Street and more recently northward from N.E. 4th in the Union Avenue-Duvall Avenue corridor. This site lies in the path of this growth and is a logical and timely extension of the trend in the area. DISTRICTS OBJECTIVE: Districts should be identified and their integrity preserved. (4) Transitional areas should be converted form one use to another as soon as possible, with new uses designed to be compatible with existing uses of the district. The proposed project with its variety of densities and types of housing, provides a logical transition from the commercial and high-density residential uses on and near N.E. 4th Street to the single family area north of the site. The clustering of residential areas within the site combined with the amenities provided each cluster offers the potential for small new neighborhoods to form within the larger development. (iv) RESIDENTIAL GOAL: To encourage suitable housing and living environments. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page S NEIGHBORHOODS OBJECTIVE: Sound, viable neighborhoods should be created and/or maintained; and declining neighborhoods should be revitalized. (1) Housing densities and types to suit a variety of family sizes, age groups, life styles, and income levels should be encouraged. (9) Housing alternatives should encourage a variety of choices in architectural design, physical location, building arrangement, and ownership patterns. The proposed development includes single family detached residences, townhouses, and apartments of varying sizes. The structures themselves are of varying heights and styles, and they are grouped in different locations around the site and in differing densities. HOUSING DENSITY OBJECTIVE: The density and location of dwellings and mobile homes should take into consideration natural features, the character of the area, community facilities, utilities, and transportation facilities. (2) All dwellings and mobile homes should have a full complement of urban utilities, access, and community facilities. (3) Multi-family dwellings and mobile home parks should be located near arterial streets to assure adequate access. (4) Single family dwellings should be buffered by low density multiple family uses from _ more intense uses. (8) Multi-family dwellings and mobile home parks should be located near employment and shopping centers. The proposed development meets all of the above objectives for housing. IMPACT ON THE AREA OBJECTIVE: Dwellings and mobile home parks should have a minimal impact on the site and be compatible with the surrounding area. (4) The site plan should provide efficient and functional use of land with attractive design. (5) To retain arterial streets for the primary purpose of traffic movement, access directly to arterials should be minimized, while access from local streets should be encouraged. (7) Significant natural features should be preserved and incorporated into site development. Through a master planning approach the applicant is able to combine a functional use of the site, preservation of natural features, emphasis on local streets, and efficient and limited access to arterial streets. (viii) UTILITIES GOAL: To ensure an adequate supply and equitable distribution of utility services. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 9 GENERAL OBJECTIVE: Utilities should be well planned, located, designed, constructed, and maintained and should be upgraded where necessary. (1) Developers and/or public and private utility agencies should provide a complete utility system appropriate to the development. The applicant is extending all the necessary utilities to the site and providing for complete and adequate facilities within the site. NORTHEAST PLAN LAND USE OBJECTIVE: The Land Use Element of the Northeast Quadrant Comprehensive Plan is intended to be a general guide to land use decision making. (1) Land use decisions within the Northeast Quadrant should be consistent with available transportation, community facilities, and utilities. (3) Land development should progress logically from west to east ... As pointed out in other sections of this report, public services and facilities are available at or near the location of the proposed development and combined with on- site improvements, can accommodate the needs of the project. TRANSPORTATION OBJECTIVE: The Northeast Quadrant Plan proposes an integrated transportation system, including private vehicles and pedestrian/bicycle facilities. (5) Pedestrian and bicycle paths and trails should be developed between residential and commercial areas to minimize the requirement for vehicular trips to provide for convenience shopping. The development has an extensive system of pedestrian pathways connecting the residential areas to each other, to the small office and commercial area within the project, and to the commercial area on N.E. 4th Street via connections to Union Avenue and Duvall Avenue. Additionally, a bicycle path will be included on the portions of Duvall Avenue adjacent to the site. C. That since the last previous land use analysis of the area zoning of the subject property, authorized public improvements, permitted private development or other circumstances affecting the subject property, have undergone significant and material change. In the time since a rezone was approved for a portion of the site in 1983, the rate of development and infrastructure improvements in the vicinity has increased. Circumstances that support the proposed rezone are: 1) The subject site lies between two arterials, along which there has been substantial single family, multifamily, and commercial development since 1983; 2) A third arterial, N.E. 4th Street, which is approximately 600 feet to the south, also has seen substantial development between Union Avenue and Duvall Avenue since 1983; prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHART April 21, 1992 Page 1 c, 3) Significant numbers of new apartments and single family houses have been constructed on properties to the south, west and east of the property; 4) Two community-sized commercial centers have developed nearby, one at the intersection of Union Avenue and Duvall Avenue and the other at Duvall Avenue and Sunset Avenue, providing sufficient services to conveniently support increased residential development in the area; 5) The proposed pattern of reclassifications and development is consistent with existing zoning designations and land use patterns in the immediate area, as the most intense land uses lie to the south and the least intense to the north; 6) The range of types and densities of proposed residential uses is consistent with those both present and desired in the area; 7) Duvall Avenue, N.E. has undergone substantial capacity and safety improvements between N.E. 4th and Sunset Avenue, N.E.; 8) The intersection of N.E. 4th Street and Duvall Avenue, N.E. has been improved to provide safer access for a greater number of vehicles to and from Duvall Avenue; 9) Metro has designated Duvall Avenue as a potential route for new service because o' the increased number of residential units built or planned along the arterial; 10) Increased recreational facilities have been developed or are planned, thereby making it possible to serve a greater number of residents than in 1983. Another test to determine whether a rezone is appropriate is the question of timeliness. Is it appropriate to rezone the subject property at this time? The Northeast Renton component of the Comprehensive Plan has been designated for substantial growth in both single family and multiple family households between 1990 and full development of the Plan area, with the population projected to increase from 43,050 to 110,000 during this period. The project provides housing for a population which is growing now. The Plan calls for a "logical and timely progression" of growth which the phasing of the proposed development permits, as it begins with single family development, progresses to townhouse and multifamily development, and concludes with office and related commercial uses. Because of the size of the property, necessary infrastructure, recreational, and transportation improvements can be developed at the applicant's expense in advance of or simultaneously with development, thereby accomplishing a goal of the Plan to minimize the burden on City services. The site itself is suitable for development because it is essentially vacant, portions of it are in disrepair, and it is located in an area of East Renton which has seen similar development over the last decade as well as construction of two shopping centers and ancillary commercial areas adequate in size to serve the growing area population. Adequate services exist now or will exist as development takes place through either installation by the applicant or a series of mitigation measures: prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 11 1) The levels of service on streets affected by the development are at acceptable levels now and are projected to remain so after full buildout of the project. In fact, traffic mitigation fees generated by the project will help fund traffic improvements slated for the N.E. 3rd/N.E. 4th Street Transportation Benefit Zone in East Renton. 2) Water and sewer capacity exists off the site and extensions will be provided by the applicant. 3) Off-site storm water flows can be maintained at or below existing levels through the storm water management system which utilizes a series of natural features (e.g., retained vegetation, biofiltration, wetlands) and designed facilities (e.g. swales, wetland enhancements, detention pond.) 4) Adequate capacity exists in the local middle school and high school to accommodate the anticipated number of children in the project. Currently the closest open elementary school is at capacity. Because of the phasing of the residential units and the uncertainty of enrollment trends, it is unknown whether or not capacity will exist for the projected number of elementary children at the time of their enrollment. Should the City impose a school mitigation fee, the applicant will pay it at the time of building permit application. 5) Numerous park facilities are located nearby, and the project should not adversely affect any of them as the applicant is providing on-site recreational facilities with the townhouse and multifamily portions of the project and is paying a mitigation fee to be applied toward additional off-site recreational facilities. 6) Provision of an extraordinary police services surety device ensures that the City is reimbursed for extraordinary police services should they be needed for the multifamily portions of the development. 7) To ensure adequate fire protection, the applicant will either install sprinkler systems in all dwelling units or pay a fire mitigation fee. Finally, staff believe approval of the proposed rezones is timely because of the numerous years this project has been under consideration and the reduction in overall density from that originally proposed and from that permitted on the presently zoned R-2 and R-3 portions of the site as well as that permitted on the G-1 portions proposed for rezone to R-3: The R-2 zone permits two dwelling units up to a density of 12 DU/AC; the applicant proposes to rezone the area to R-1 and construct single family residences at a density of 3.7 DU/AC. Under current zoning, the R-3 portion of the site could be developed with multifamily dwellings at a density of up to 25 DU/AC. Instead, the applicant is proposing to rezone part of it to R-1 and build single family residences at a density of 3.7 DU/AC. The remaining part of the R-3 zone will be developed with 63 townhouses at a density of 7 DU/AC. The R-1 zoning proposed for the G-1 parcel permits single family development at 6-8 DU/AC; the applicant is proposing to develop 16 lots on this portion of the site for a density of 3.5 DU/AC. prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARD: April 21, 1992 Page 1; The R-3 zoning proposed for the three G-1 parcels permits multifamily development at up to 25 DU/AC. The applicant is proposing to build 276 apartment units on these three sites at densities of 11.5 DU/AC, 15.3 DU/AC, and 19.6 DU/AC. 5. SITE PLAN APPROVAL CRITERIA - Section 4-31-33(D)(1) lists ten criteria that the Hearing Examiner is asked to consider, along with all other relevant information, in making a decision on a Site Plan Approval application. These include the following: a. Conformance with the Comprehensive Plan, its elements and policies; The discussion in section G.4.b. of this preliminary report addresses the conformance of the proposed project with the Comprehensive Plan. b. Conformance with existing land use regulations; The 119 single family dwelling units generally meet or exceed the requirements of the R-1 Residential Zone, R-2 Residential Zone, Site Plan Review, Parking and Loading Ordinance, and Subdivision Ordinance. The 119 single family dwelling units located in the R-1 zone comply with the requirements of that zone. For example, lot areas vary from 7,200 square feet to 10,025 square feet, compared to the required minimum of 7,200 square feet; density is 3.8 DU/AC compared to the maximum permitted of 6 DU/AC. The single family portions of the project also have been designed to address unique site characteristics such as the two wetlands, an existing drainage swale, and stands of largr: trees. The 63 townhouses and 276 multifamily units contained in the R-3 zoned portions of the site generally meet or exceed the requirements of the R-3 Residence District, the Site Plan Review, the Landscape Ordinance, and the Parking and Loading Ordinance. The permitted density in the R-3 zone is 25 DU per net acre with the minimum lot area being t 7,200 square feet; the proposed density ranges from 11 .5 DU/AC to 19.6 DU/AC per acre, and the lot areas exceed 7,200 square feet. Development standards are satisfied for lost size, configuration and dimension, building heights, setbacks and lot coverage. The number of parking spaces meets the requirements established in the Parking and Loading Ordinance. Retention of natural vegetation and wetland areas and creation of landscaped areas as required in conjunction with environmental and land use review of this project (see other sections of this report) will ensure compliance with the Mitigation Document and the Landscape Ordinance. C. Mitigation of impact to surrounding properties and uses; Potential impacts to the surrounding properties and uses have been identified in the areas of housing and land use, aesthetics and natural environment, traffic circulation, recreation, and public services and utilities. The Environmental Review Committee issued a Mitigation Document on December 2, 1991 to address the above-mentioned environmental impacts of the proposed development. Similarly, conditions recommended in conjunction with this site plan review are intended to mitigate impacts on surrounding properties and uses. As mentioned previously in this report, the Northeast Renton Plan indicates that there is a need for additional housing in this sector of the City and that the site is well-suited for the prelmrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 13 type of housing proposed by virtue of its location in an area which contains both single and multifamily housing and the necessary supporting commercial services and transportation facilities. The proposed development will provide 458 dwelling units (replacing two single family houses) to house a projected 898 persons. Thus the development should have a positive impact upon housing. The applicant, working with City staff over the past two years, has endeavored to make the proposed residential and commercial structures compatible in scale, design, and density with surrounding uses. Single family uses have been located near existing areas of single family residences; multifamily and commercial uses have been oriented to Duvall Avenue and the multifamily and commercial uses south of the site. The scale of the townhouse and multifamily dwellings has been established to be consistent with other multiple unit dwellings in the area. Townhouses have been set back from single family uses as well as from Duvall Avenue and the internal neighborhood collector (Anacortes Avenue.) Multifamily units have been set back from all streets and from adjacent properties, and parking spaces have been placed internal to the multifamily areas. Pathways have been located to provide easy access among the various internal uses and between the residential areas and the transit stops and the office/commercial area. Pedestrian-scale lighting has been provided for safe access during evening hours. In general, the three recreational facilities have been located away from the majority of residential units and with adequate open space. Vehicular access for all residential areas has been oriented to the internal street system. Access to the office/commercial area has been oriented to Duvall Avenue with no access through residential areas. Future transit stops have been located on Duvall Avenue at two locations, one convenient to single family residences and one convenient to the multifamily units. A bike path has been located on Duvall Avenue as part of the City's bicycle trail system. d. Mitigation of impacts of the proposed site plan to the site; Potential impacts to the site have been addressed through the aforementioned Mitigation Document and through conditions established in conjunction with this site plan review. The site plan has been configured to protect the on-site sensitive areas, especially wetland areas. Four major wetlands have been enhanced and enlarged to compensate for the nearly one-acre of filled wetland areas. Wetlands and their buffers will be placed in separate tracts and where buffers intrude into single family lots (e.g. lots 6, 41, 42, 43, 44, 50, 51, 52, 53, 54, and 55 on the preliminary plat map) they will be placed in Native Growth Protective Easements until such time as zoning permits lots less than 7,200 square feet, at which point the NGPEs will be added to the tracts. Wetlands will be separated by fencing from adjacent residential uses and appropriate signage will be placed along the buffer edge. A Wetland Mitigation Plan detailing buffer plantings, maintenance, and monitoring is required prior to the issuance of building permits. To accommodate the proposed development a substantial portion of the existing vegetation will be removed. The applicant has submitted a tree inventory/landscape plan which calls for the retention of significant trees as feasible and the introduction of new plantings suitable for the terrain and planned uses. Street trees will be planted along all streets and entry points will be landscaped. pelm,p[ PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 14 e. Conservation of area-wide property values; The proposed development should have a positive effect on area-wide property values by 1) Establishing residential and commercial uses on property which is essentially vacant; 2) Eliminating vehicles, appliances, and other refuse which have been dumped in certain areas; 3) Restoring the functional and aesthetic values of wetland areas which have been disturbed by off-road vehicles; 4) Locating new development in an area designated as appropriate and desirable for such use by the Comprehensive Plan; and 5) Providing a scale and density of development compatible with that on other properties in the area. f. Safety and efficiency of vehicle and pedestrian circulation; On-site: Vehicle access and circulation plans have been designed in response to Transportation Division requirements and City codes. The alignments of N.E. 8th Street and N.E. 6tn Street have been prescribed to meet the overall street grid in the area and to provide limited, safe access points into the residential portions of the site. All direct access to residential areas is from internal streets which serve as neighborhood collectors. Vehicle access to the office/commercial area is from Duvall Avenue only. Pedestrian pathways have been provided throughout the development linking residential areas to one another, to recreational facilities, to the office/commercial area, and to future transit stops on Duvall Avenue. Pedestrian pathways have also been located on the perimeter of wetland buffer areas as appropriate. Pedestrian-scale bollard lighting has been F placed along pedestrian pathways for safety purposes. Off-Site: Improvements will be required to Duvall Avenue at the intersections of N.E. 8th Street and N.E. 6th Street and along the length of the site, including the provision of a 4 foot wide bike path on the shoulder. A TBZ fee will be paid toward other off-site improvements needed in the NE 3rd/NE 4th corridor. The applicant and City staff continue to work with Metro to obtain transit service on Duvall Avenue. g. Provision of adequate light and air; The townhouse and multifamily residential structures in the development have been generally designed and sited so that they are adequately separated from site boundaries and from other residential structures (a minimum of 25 feet) in order to provide for adequate light and air and to minimize the impact of shadows. Similarly, the location of parking facilities and outdoor private and common ,spaces should serve to ensure that residential units receive sufficient light and air. preimrpt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 15 Staff will recommend that outdoor private spaces for ground-level units be screened to provide privacy and defensible space, while allowing for adequate light and air. h. Mitigation of noise, odors, and other harmful or unhealthy conditions; Residential structures have been located a sufficient distance from Duvall Avenue and internal streets so that noise from street traffic should not significantly impact residents. Additionally, landscaping between the street and abutting structures should serve to lessen the impact of noise. Internally, residential structures are separated by sufficient distances so that internal noise should not have a significant impact on other residential units. Landscaping elements between structures should also help to lessen noise impacts between structures. Recreation buildings and outdoor pool areas have been sited at the periphery of residential complexes in order to minimize the number of dwelling units affected by noise. Additionally, residential structures have been sited to minimize the number of units abutting the office/commercial area. Only 3 residential buildings abut this area. To lessen noise impacts from the parking area for the office/commercial area, the intervening space is fenced and heavily landscaped. Because the site is proposed for residential and office/commercial use, harmful odors are not anticipated. L Availability of public services and facilities to accommodate the proposed use; and As mentioned elsewhere in this report, public services and facilities can generally accommodate the uses proposed for the project, but utilities will have to be extended to and through the site by the applicant. Special measures will need to be undertaken to provide sanitary sewer service and to manage storm water runoff in a manner which protects the integrity of the wetlands and accomplishes detention goals. The Orchards is one of nine projects which was granted a limited exemption from the East Renton sewer moratorium. Additionally, an inter-basin transfer solution has been approved for the project until such time as additional sewer capacity is made available. The applicant must construct the inter-basin transfer facilities prior to the issuance of any building permits for the project and has agreed to do so if adequate capacity does not exist. Water service also is available to the area, but the applicant will have to extend water mains from nearby arterials into the site. The on-site distribution system will also be constructed by the applicant and will consist of 12, 10 and 8-inch mains, which will supply an adequate fire flow to all components of the project. Fire service is anticipated to be adequate with the addition of sprinkler systems in single family residences or the payment of a fire mitigation fee to defray the cost of additional service. Assuming the customary number of calls, police resources are adequate to serve the project. Should the number of calls be greater than normal, compensation for additional service will be provided through a special surety device for such purposes. A conceptual plan for storm water management has been approved for the project, as has a preliminary wetland mitigation plan. The applicant continues to work with Storm Water prel—pt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 16 Engineering staff to obtain approval for specific design plans and for the timing of the required improvements. A detailed wetland mitigation plan will be completed by the applicant and approved by Development Services staff prior to the issuance of any building permits. Middle and high schools have adequate capacity to serve the projected resident student population. The ability of the school district to serve the elementary school resident population will depend on the timing of future phases of construction and the capacity of the district at that time. Finally, recreation facilities in the area combined with those provided in the development and the mitigation fees to be paid by the applicant should ensure that an adequate level of recreational services and facilities are available to resident. j. Prevention of neighborhood deterioration and blight. Staff view this development as having a positive impact on the existing area. As mentioned earlier in this report, the project will bring additional residents into the neighborhood, provide development compatible with the surrounding area, and improve the visual character of portions of the site. New residents should help bolster the identity of the neighborhood as well as the local economy. All of these factors should help prevent neighborhood deterioration and blight. H. DEPARTMENTAL RECOMMENDATION: Because of the binding nature of the site plan review process, staff believes that regular rezones to R-3, Residence District, are more appropriate than the contract rezones requested by the applicant. Resolution 2880 deemed that site plan review satisfies the condition of Ordinance 3795 that PUD approval be obtained by the applicant for this project. According to the provisions of the Site Plan Review process (Section 4- 31-33 of the Zoning Code), major adjustments ("involving more than a 10% change in area or scale") cannot be made to an approved site plan without additional review, including a public hearing before the Hearing Examiner. Staff believes that these provisions accoml(sh the same purpose as that intended by the requested contract rezone, namely that no greater development,,tiavl6t approved through the present prgcess for the R-3 zoned portions of the project without further scrutiny by staff, the public, and the Hearing Examiner. Staff recommend that the Hearing Examiner take the following actions with respect to the application from Northward Properties, (File Number ECF-138-90): 1. Recommend to the City Council approval of the following rezones: Approximately 3.46 acres from G-1, General Zone to R-1, Residential Zone (Parcel A); Approximately 28.14 acres from G-1, General Zone, R-3, Residence District, R-1, Residential Zone, R-2, Residential Zone to R-1, Residential Zone (Parcel B); Approximately 9.05 acres from R-2, Residential Zone and R-3, Residence District to R-3, Residential Zone (Parcel C); Approximately 3.21 acres of G-1, General Zone to R-3, Residence District (Parcel D); Approximately 7.04 acres of G-1, General Zone to R-3, Residence District (Parcel E); prei—pt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 17 Approximately 2.21 acres from G-1, General Zone to B-1, Business District (Parcel F);and Approximately 9.17 acres of G-1, General Zone to R-3, Residence District (Parcel G); 2. Because of the size of the proposed development, the physical location of various components, the variety of uses and types of housing, and the applicant's and the staff's desire that the development should be phased over a period of years, staff is recommending that the site plan be approved for a 5 year period instead of 2 years, as permitted by Section 4-31-33 (J) of the Zoning Code. The recommended phasing is: 119 Single Family Lots: 1992-1 994 63 Townhouses: 1993-1995 276 Multifamily Units: 1993-1996 28,000 Square Feet of Office/Commercial: 1 994-1996 Further, staff recommends approval of the site plan application to allow the phased development of The Orchards mixed-use project consisting of 119 single family lots, 63 townhouses, 276 multifamily dwelling units, approximately 28,000 square feet of office and commercial space in three buildings, three recreation centers, related parking spaces, detention facilities, and wetlands and other open areas on the 62.3 acre site, subject to the requirements established in the Environmental Mitigation Document of December 2, 1991, to the necessary rezones, andiI the following conditions to be approved by the Development Services Division prior to the issuance of building permits for any phase of the project:: a. The applicant shall provide street improvements on N.E. 8th Street and Duvall Avenue, N.E. as required by the Subdivision Ordinance (Section 9-12, Renton City Code); b. The applicant shall provide the following modifications to the single family portion of the site plan to be approved by the Development Services Division prior to the issuance of any building permits for this portion of the project: 1) Provide pedestrian-scale lighting bollards on the pedestrian pathways between lots 9 and 10 in Sector A and along the pathway connecting this path with the one in Division 1; between lots 40 and 41 in Division 1; and between lots 26 and 27, 41 and 42, and 48 and 49 in Division 2; and 2) Easements or tracts at least 15 feet wide for all paths within which no structures, including fences, shall be permitted; C. The applicant shall provide the following modifications to the site plan for the townhouse portion ( "C" on the Site Plan) of the development to be approved by the Development Services Division prior to issuance of any building permits for this portion of the project: 1) 32 Off-street visitor parking in small areas dispersed throughout the complex, with at least one parking area located near the recreation center; 2) Pedestrian-scale bollard lighting along the pathways connecting the area near Buildings 6 and 8 with Duvall Avenue, N.E.; pret—pt PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 18 3) A sidewalk adjacent to the internal loop road which shall provide a connection among Buildings 13 and 14 and the recreation center; 4) A sidewalk adjacent to the internal loop road connecting Buildings 17 and 1 8; 5) All paths to be at least 6 feet wide; and 6) Provide outdoor seating in the mailbox area; d. The applicant shall provide the following modifications to the site plan for the multifamily portions ( "D", "E", and "G" on the Site Plan) of the development to be approved by the Development Services Division prior to issuance of any building permits for this portion of the project: 1) Easements and concrete base for the Metro transit stop on the west side of Duvall Avenue, N.E. south of N.E. 6th Street; 2) An extension of one of the two paths on the east side of area "E" to Duvall Avenue, N.E. near the future Metro transit stop; 3) An extension of the path between Buildings 12 and 13 from area "E" into area "F"; 4) Pedestrian-scale bollard lighting along paths; 5) Relocation of mailboxes to locations which are more centralized and provide easy 3 vehicular access for the Postal Service, and the addition of outdoor seating at each location; 6) An increased number of lighting fixtures in open parking areas; 7) The addition of at least one pedestrian "walk zone" between parking spaces equal to half the width of a standard parking space in front of each residential structure and at the termination point of each rear entry and pedestrian path; 8) A "drop-off" zone and reserved parking near each recreation center; 9) Dumpsters screened and located only adjacent to carports or other structures within parking areas; 10) Bicycle storage areas in each area; 1 1) Within code requirements, building setback modulation along Duvall Avenue and Anacortes Avenue; 12) Additional spacing between Buildings 6, 7, and 8 in area "G" to improve view outlook and visula privacy between units; 13) Walls between outdoor patios for ground-level units; 14) Within each complex, a children's outdoor play area, including equipment; and 1 5) Deciduous trees of at least 2 inch caliper at the time of installation; prelmrpt • 4 PRELIMINARY REPORT TO THE HEARING EXAMINER THE ORCHARDS April 21, 1992 Page 19 e. The applicant shall provide the following modifications to the site plan for the office/commercial ("F" on the Site Plan) of the development to be approved by the Development Services Division prior to issuance of any building permits for this portion of the project: 1) Low fencing and additional landscaping to provide a clear separation between residential and commercial areas and to reduce headlight glare from the commercial area into residential units; and 2) Outdoor seating areas for patrons of businesses as appropriate. 3. Approve the preliminary plat for Sector A, Division 1 and Division 2 subject to the requirements established in the Mitigation Document of December 2, 1991, the necessary rezones, and the following conditions: a. The applicant shall provide the required easement and concrete base for the future Metro bus shelter on the west side of Duvall Avenue, N.E. south of N.E. 8th Street. b. The applicant shall establish Native Growth Protective Easements in lots 5 and 6 (Division 2) and lots 41-44 (Division 1) for the wetland buffers. C. The applicant shall include in purchase and sale agreements provisions whereby the NGPEs will be added to the tracts containing the adjacent wetlands if future zoning provisions permit such transfers. d. Lots in Sector A, Lots 40-43, in Division 1, and Lots 43-49 in Division 2 are approved subject to the necessary rezones. 4 prelmrpt DDDDS ENGINEERS, INC. 4205 14BTH AVE. N.E., SUITE 200 - BELLEVUE, WA 9EI007 [2061 BB5-7B77 OR 454-3743 TELECORIER [206) BB5-7963 TRANSMITTAL DATE 4 f 17/92 JOB NO. 88008 TO_ City- of Renton ATTN: Mr, Randall Parsons Department of Public Works- - REF: -The- Orchards- - - - 200 Mill Avenue South _ _ _ _. __ __ ._ _ . . . ._ . . Renton, WA 98055 _ _ __ _ _ _ _. . . .. MAIL _ _ DELIVER X PICK UP .... __ OTHER PLEASE FIND: ATTACHED _ X __ UNDER SEPARATE COVER. ORIGINAL _ _ PRINTS __ _ COPY , X PRELIM . FINAL CALCS _ ____ DESCRIPTIONS __ OTHER QUANTITY DATED DESCRIPTION 1 set _ _ Level 1 Off-site _Analysis__ TRANSMITTED FOR: YOUR USE X_ PER REQUEST __ _X INFORMATION ONLY ACTION REQUIRED: PROCESSING _ X ... REPLY RETURN .... . . .... NONE COMMENTS Randall, the additional information for the downstream analysis is included in this_report. _It is to _replace the Level _1 Analysis in the previous_Drainage report. Please call Ed Jones . or .myself .if you have . . any questions or comments. CC: Craig _Krueger., Northward BY: Gar R. Sharnbroich, E. I.T. • i ® � DODOS ENGINEERS, INC. 4205 14BTH AVE. N.E., SUITE 200 - BELLEVUE, WA 88007 [2061 BB5-7877 OR 454-3743 TELECOPIER [2061 BB5-7963 TRANSMITTAL DATE _ Z '. .I Z JOB NO. S8 t S.M ATTN: ... ._........�7!0�4 -. 01. s.�.T".G _._ .._ PV�jV�C. WO'2+K- F � REF: _ _............. MAIL DELIVER _ PICK UP OTHER PLEASE FIND: ATTACHED UNDER SEPARATE COVER ORIGINAL PRINTS COPY T°_ PRELIM FINAL CALCS DESCRIPTIONS OTHER QUANTITY DATED DESCRIPTION fit.► ...+�ti .ljT«.. t, ..._... souses Eawolmo a3AGMU tjoj)M:l0 _ _ ............__ ..... .__ TRANSMITTED FOR: YOUR USE x PER REQUEST INFORMATION ONLY ACTION REQUIRED: PROCESSING ;><. REPLY _ RETURN NONE COMMENTSC.... . g e-._ ,. 1. o.sT. D_ eOTLA66....i,J/a.'�"t'A�Gi yov12- _ 1 uEs _ ............ ...... ....... ..... . . . .......................... ........ DODDS ENGINEERS, INC. 4205 14BTH AVE. N.E., SUITE 200 - BELLEVUE, WA 9B007 [206] BB5-7B77 OR 454-3743 TELECOPIER [206] Be5-7963 TRANSMITTAL DATE _2/11/92 JOB NO. 88008 TO __Utilities Section _ _ . . . ATTN: Randall Parsons, P.E. City of Renton _ _ REF: _Orchards 200 Mill Avenue South Renton, WA 98005 MAIL X DELIVER _ _ __ PICK UP .. . . . . . . . OTHER PLEASE FIND: ATTACHED _ X _ UNDER SEPARATE COVER ORIGINAL PRINTS _ _ X COPY ___ _ PRELIM _. FINAL CALCS DESCRIPTIONS _ _ _ OTHER QUANTITY DATED DESCRIPTION 1 _ _ Preliminary Plat Preliminary Grading & Utility Plan_ .... ......... . .... . ................ ........ . ........ .. ........... .._._. FEB 1 N 1992 ............ .......... . ....... ... ..... . . . ......... . ... ..... ............ . CITY OF.RENTONEngin Bering Dept. TRANSMITTED FOR: YOUR USE -X. PER REQUEST INFORMATION ONLY. ... . ACTION REQUIRED: PROCESSING REPLY.. . .... RETURN . . . .. . NONE COMMENTS These .are transmitted to supplement_the storm_ drainage calculation submittal. CC: _ _ _ _ _ _ _ _ BY: EZda nes, P.E. CITY OF RENTON MEMORANDUM DATE: February 20, 1992 TO: Reviewers of The Orchards FROM: Bill Stalzer SUBJECT: The Orchards site plan and preliminary plat review Attached is the revised submittal for The Orchards mixed-use development. Modifications have been made to the site plan submitted in October of 1990 based on the EIS mitigation document and surface water design issues. To assist you in your review, I am enclosing a copy of the mitigation document issued by the ERC and a copy of the comments your division made on the project at an earlier date. Because of the tight Hearing Examiner's schedule for this project, I should appreciate it if you could complete your review and have comments back to me no later than Friday, March 6th. Please let me know if this is not possible and if you have questions about the project, feel free to call me at x2518 or 682-2116. ® � DDDDS ENGINEERS, INC. CIVIL ENGINEERING S U R V E Y I N G R L A N N I N G February 10, 1992 DEI Project No. 88008 n C��II�I Mr. Randall Parsons, P.E. Utility Supervisor Utility Systems Division F E B t N i992 City of Renton 200 Mill Avenue South Renton WA 98055 CITY OF RENTON Engineering Dept. Subject: The Orchards Dear Mr. Parsons: Attached is the storm drainage calculations and prints of the proposed grading and utility plan and preliminary plat for the Orchards project. We have prepared these documents in accordance with the Orchards mitigation agreement, the King County Storm Drainage Manual and our discussions with you in a predesign meeting on December 19, 1991. I have summarized the following main points discussed in that meeting. 1. The west basin detention would be provided in Wetland #1 (to be enchanc--d). Offsite runoff will be directed to a wetland swale traversing the site and bypassing Wetland #1. One third of the 2 year offsite peak flow shall be metered into the Wetland #1 enhancement area. Detention storage shall compensate for this additional flow. Onsite flows shall be biolfiltered prior to entering the detention system. Biofiltration facilities may be located within the wetland buffered areas. Access roads shall be provided to all facilities for maintenance. 2. The majority of the east basin detention would be provided within Wetland #7 located in the southeast portion of the site. Detention shall be provided for the 2 year storm within Wetland #3 central to the site with provisions for overflowing the 100 year storm event. Wetland #4 central to the townhouse portion of the development would also be available for detention. Since the main portion of offsite is not bypassed for the east basin detention, a performance check shall be completed. This check shall compare the proposed performance hydrograph at the discharge point with a performance hydrograph generated by summing individual detention discharges for each sub-basin within the east basin development. Biofiltration and access shall be required as stated for the west basin. 4205 14BTH AVE. N.E., SUITE 200-BELLEVUE, WA 98007 [206] 865-7B77 OR 454-3743 FAX:[206]BB5-7963 February 10, 1992 DEI Project No. 88008 Mr. Randall Parsons Utility Supervisor 2nd Page Subject: The Orchards WEST BASIN The west onsite basin is 16.4 acres in size. There are five sub-basins within the west basin. Only the central and southern most basins have a well defined discharge point. The remaining sub-basins sheetflow across gravel access drives or into the rear yards of the neighboring properties. In order to not adversely affect the neighboring properties, we are proposing to combine the four northern most sub-basins and provide detention within wetland #1. The southern most sub-basin will provide a detention system within the 2.8 acre multifamily section located south of NE 6th Street in the southwesterly corner of the project. The existing onsite swale will be relocated to align it with the proposed lot lines. The swale will bypass wetland #1 by intercepting it at the northeast corner of the wetland by a pipe system. The pipe system will convey offsite water around the north, west and south sides of the wetland to its natural discharge point. A control structure will be located at the northeast corner of wetland #1 to meter out one third of the 2 year offsite swale flow to the wetland. Detention will be provided in order to release the developed onsite 24 hour - 2 year storm at 1/2 the existing 24 hour - 2 year storm runoff rate; the developed onsite 24 hour - 10 year storm at the existing 24 hour - 2 year storm runoff rate; and the developed 24 hour - 100 year storm at the existing 24 hour - 100 year storm runoff rate. Since the standard peak rate runoff control performance is exceeded by the above criteria (i.e. existing runoff rates will be reduced) the safety factor of 30% need not be applied to the calculated detention volumes. Water quality facilities will be provided to treat onsite runoff prior to entering the detention facilities. Three separate biofiltration swales are proposed. One located at the northwest corner of the detention area, one located at the southeast corner of the detention area and one located along the east margin of Anacortes 200 feet south of NE 8th Street. The swales will be designed as etland�swales with a design water depth of 8 inches. 2G� l f Cam/ � P2 e East Basin V-0 r The east onsite basin is 45.9 acres in size. The entire east basin combines to discharge to an existing 36 inch culvert at the south property line within Duvall Avenue NE. The north-central portion of the east basin has five depression areas within it. These areas are dry during the summer months, but contain water within the wetter winter months. All existing hydrograph generations assumed the conservative condition that the depression areas were dry as an initial condition. On and offsite hydrographs were routed through these depression areas for establishing the same discharge requirements as stated above for the west basin. February 10, 1992 DEI Project No. 88008 Mr. Randall Parsons Utility Supervisor 3rd Page Subject: The Orchards EAST BASIN (continued) A portion of the detention was provided within wetlands #3 and #4 with the major portion being provided within Wetland #7. Water quality facilities include a wetpond east of Wetland #3 with additional biofiltration swales dispersed throughout the site. The performance check was conducted and is summarized in the following table. The west basin was divided into three subbasins each with its own detention system. The east basin was divided into four sub-basins each with its own detention system. The discharges from these detention systems were summed with the offsite hydrograph flowing through the site. These values were then compared with the proposed "regional" detention systems within the existing wetland. In each case the ultimate discharge was less for the proposed "regional" system verses the individual systems. RAR III: PRELIMINARY ROUTING SUMMARY JANUARY 31, 1992 _ BY: GARY R. SHARNBROICH, E.I.T. EST$ .::. € PROPOSED 'INDIVIDUAL PROPOSED I LNDIVIDU. 1 PROPOSED DETENTION DETENTION DETENTI, ) lJ DETEN T iON DETENTION _ SYSTEM SYSTEMS SYSTEM_ I, SYSTEMS SYSTEM_ EX. 1l2 211 R PEAK FLOW RATE 1.6 Cfs - 12 Cfs - 0.14 cfs DEV. 2YR PEAK FLOW RATE 1.6 cfs , 1.7 cfs 2.2 cfs_�� 2.8 cfs jj 0.14 cfs EX. 2YR PEAK FLOW RATE � 3.2 cfs - 4.1 cfs !t -- � 0.3 cfs DEV. 1OYR PEAK FLOW RATE 3.2 cfs 3.2 cfs 4.1 cfs 4.8 cfs 1 0.3 cfs EX. IOOYR, 241IR PEAK FLOW RATE 14.8 cfs 1 - 23.2 cfs - 1.4 cfs DEV. IOOYR, 24HR PEAK FLOW RATE 12.1 cfs 13.6 cfs 15.4 cfs 15.3 cfs 1.0 Cfs EX. 100YR, 7DAY PEAK FLOW RATE 12.4 Cfs - 19.5_ds -_ _ 1.1 cfs DEV. 100YR, 7DAY PEAK FLOW RATE .3 efs 15.0 cfs t Cfs 24.6 cfs 1 1.0 cfs 2YR DETENTION VOLUME (ct) 23,416 35,556 211,070 133,010 1 4250 10YR DETENTION VOLUME (cf) 31,909 56,510 318,149 211,363 11 '7050 100YR, 24HR DETENTION VOLUME (ct) ! 41,296 61,148 394,376 275,581 7700 100YR, 7DAY DETENTION VOLUME (c0 I 47,497 63,392 404,441 295,664 7700 February 10, 1992 DEI Project No. 88008 Mr. Randall Parsons Utility Supervisor 4th Page Subject: The Orchards This is a complex drainage system and analysis and we expect you will have some questions. We tried to organize our calculations in a logical format to facilitate your review. We will be available at your convenience to answer any questions you may have regarding the attached documents or provide additional information. You may contact us at 885-7877. Sincerely, DODDS ENGINEERS, INC. c-e E ar . ones E. ETJ:sab cc: Craig Krueger, Northward 97C;EIVeD PU7-U(,; V--A>i'K3 DEPT. Ure OF R&'TON King County Surface Water Management Division Department of Public Works 730 Dexter Horton Building 710 Second Avenue Seattle,Washington 98104 (206)296-6585 i I June 18 1991 ` Mr. Lynn Guttman ,;t)i`i 011 Department of Public Works Gin OF RENTON City of Renton j 200 Mill Avenue South Engineering Deptu Renton, WA 98055 RE: Drainage Issues in the Proposed Orchards Plat Dear Mr. Guttman: Please allow me to express the interest and concern of King County Surface Water Management Division staff regarding the proposed plat of The Orchards, near Northeast 4th Street and Duvall Avenue Northeast. I understand the project is in the Final Environmental Impact Statement stage of approval . We are concerned by possible downstream impacts to existing drainage problems, and would like to ensure coordination between our agencies in addressing these problems. There are two specific areas of concern wh ch could be impacted by The Orchards project. One of these areas i he basin draining through the plat of Puget Colony Homes. This area is ughly bounded on the west by 136th Avenue Southeast from Northeast 4th treet (Southeast 128th Street) south to Southeast 132nd Avenue. North of ortheast 4th Street, the basin extends from Duvall Avenue NortheaAt40th Avenue Southeast) and Northeast 4th Street northeasterly to ab Avenue Southeast and Southeast 124th Street. Althougheg' The Orchards project and your staff indicate that n e of the ill drain to Puget Colony Homes, there is widespread concernamon —ttieresidents of the plat about the impact of new development. The plat floods frequently due to its extreme flatness and possibly to partial filling of the wetlands between Southeast 128th and Southeast 132nd Streets. This problem was not mentioned in the October 1989 draft Maplewood Creek Basin Plan prepared for the City of Renton by Parametrix, Inc. We believe that any additional runoff through Puget Colony Homes, or through the wetland to the north, or any filling and clearing of the likely wetland area north of Southeast 128th Street (adjacent to The Orchards) , would adversely impact County and private property in the plat as well as natural resources both upstream and downstream. The second area of concern, which was addressed by the draft Maplewood Creek Basin Plan, is erosion of the natural channels leading to the Maplewood Golf Course. These streams are identified as Tributaries 302 and 303 in the 1987 • - t L�- Mr. Lynn Guttman � 5-0 June 18, 1991 Page Two j"VIA- ��, T' King County Basin Reconnaissance Report, and the West and East Forks, respectively, of Maplewood Creek in the Maplewood Creek Basin Plan. Erosion along the western tributary, part of which is within Renton, threatens the road right-of-way at the intersection of Southeast 136th Street and 138th Avenue Southeast. Further downstream, below the confluence of the two trib- utaries and upstream of Maplewood Golf Course, a concrete siltation dam was washed out this year by high flows. A regional retention/detention pond to be built by King County along Tributary 303 below the plat of Puget Colony Homes was proposed in the draft Maplewood Creek Basin Plan. While this facility would help to attenuate flows in the channel downstream, it would do ncthing to help flooding upstream. I think it would be helpful to con- sider alternative courses of action. a I hope to coordinate with your staff our review of any future plans, including The Orchards, which would affect the above-mentioned areas of concern. With the initiation of the Lower Cedar River Basin Plan by Surface Water Management Division staff, this may be an appropriate time to address drainage issues in the basin jointly. Sincerely, Jim Kramer Manager JK:RS:ad W19:LT2 cc: Ray Griffin Dave Baldwin Ken Guy,' Assistant Manager, Surface Water Management Division Curt Crawford, Acting Supervising Engineer, Drainage Investigation Unit ATTN: Randy Snow, Engineer FROM:KING COUNTY DPW/SWM TO: 206 235 2541 MAY 31, 1991 4:19PM P.01 King County Surface Water A_4anayemei_'.:. ` `, 11'('l1'llilC(1 l'l: f 1115'II\II l'f111i uepartment of l'oblic Wor•k9 -;io fxxter Horton building -10 second A\,cnuc irortic. Washington 4(:1C>•1 (20(.)296.6585 (206) 296-6519 N0106) FAX TRANSMITTAL COVER SHEET FOR FAX (206) 296-0192 Date: Jc- - 3 1 q / Number of Pages , I � � Including Cover 7 TIME: TO: A/ L L- I �I R S.D /S FAX # (Name) _S rAce- (Office FROM: �t'�V L/ 5T�A) SD/l) (Name) P" RtfC- jA 1/OL1)C01E.A1 T SNM Division Section) TRANSMITTED BY: 00,0: Name) !� ADDITIONAL COMMENTS: •12 FROM:KING COUNTY DPW/SWM TO: 226 235 2541 MAY 31, 1991 4: 19PM P.02 / den Ufu• son,public involvement Cuordinetor 2 I��I SurG,.,µ,vier Naitiigcrn 1)V.icni Ilcjam 10)1 of 1'61fr w.3 O ez'?y :z r s J � f l� �"6 FROM:KING COUNTY DPW/SWM TO: 206 235 2541 MAY 31, 1991 4: 19PM P.03 Ray Griffin APR 19 �gg� 14306 144th Ave . SE 3ienton , WA 98059 KING COUNTY (206 ) 228-5673 sURFACf WAJfR XAXjG1X[X1 DgIS10K King County Dept . of Public Works Surface Water Management Div . 710 Second Ave . Rm . 730 Seattle , WA 98104 Attn . : Jim Kramer Mgr . Dear Jim: I spoke with you at our last SWMCAC meeting about the storm water problems some residents of the East Renton Plateau are experiencing with increasing frequencies . I also asked if it would be possible to get a knowledgeable representative from your utility to come out and address the concerns of those affected at a community council meeting . Some now have their yard sep tic more an just one day . People tanks fear the effects of constant flooding and the possible health hazard should their system fail through no fault of their negligence . The water is drainage from tl)e county roads and properties above whose owners have put in drainage ditches and clear cut land in hopes of developing their acreage . In some cases King County Public Works has opened and enlarged drainage ditches and pipes then just dumped all that water onto private property flooding out the home owner living on the land used as a catch basin . While it is true that historically this is a natural water course , the amount of run off is nowhere near pre-development rates , and the flooding is a new problem . The residents being dumped upon say that a double standard is being used , because to reduce road and residence flooding above , the county increases the channel si.ze , which in turn increases flooding on properties below , and tl)e county refuses to do anything about the problems it creates by solving others ' complaints • One of the properties beirig dumped upon belong to Rick & Ginger Dickson 15630 SE 124th 228-624.4 . 7'hc storm water crosses their property then empties into Coalfield Park . you should ask around of ur the roublers spots , The wateartment o then flows find out lfrom that thearea park land down one into trouble P May Creek . FROM:KING COUNTY DPW/SWM TO: 206 235 2541 MAY 31, 1991 4:20PM P.04 Another problem area and contact person is Sandy Taylor 228-5477 living at 15243 SE 132nd Renton , WA 90859 . Her family found it necessary to dig and Jntiromdf ] oodingcherlhomeunThe her wayyard shethis put year to keep storm waters it was that , "When it rains we ha<<e a sea of mud in our back yard . " Sandy tells me that most of the residents living in her area around 52 132nd are experiencing problems that are worse now than ever before . C Cm&ter Road or SE 128tt3 as the map would identify it , near 140th SE , as water over it when we have heavy rains , this is a r►ew phenomenon that has only occurred in the last two years . We had Randy Snow out to walk him through the problem areas we were aware of inwaterOretention there pondwas betweeniCemetery increasing Rd . the andsize the storm Puget Colony where you were going to install larger drain pipes to eliminate the flooding of residences . Nothing has been accomplished yet and flooding still occurs . With our last storm on' April 4th, the amount of storm water going . � down through our green belt was so great that it washed out the dam located on Maplewood Golf Course . That concrete dam had been nly went over the in that location for over 25 years , and water o top , never around until now . Needless to say , we lost much soil due to erosion during that storm and now the land slides are starting , soon ,it will no longer be community property sliding , but residents ' yards and homes . The city of Renton is also contributing to the flows in our creek and I have had just as much success getting the city to reduce the storm flow rate as I have had with the county . NONEI Please contact me if it will be possible to got a speaker during the month of May and we can work out a date . Our Community Council atetings 160th take andPlace SEa128th .Lord The usual emeeting Lutheran timeuris located a between 7 & 9 PM. fours Truly c ` ay Griffin SEC. 10 TWP. 23 N. RGE. 5 E. W.M. IM42' ET I _ ' R I /E zn� 394.i5 R/PRAP SEE DETAIL SHT. C6 It CB 15 FOUR 4" THK. X 3' CONC CAP OVER 12" DI IN PA VEMENT AREA STA 0+83.61, 9.54' RT CTR GRT j .1G _OJR.._SR? CB 13 4 CB 14 T)-PE 2, 54 , THRU CURB `BRA TES ''�7L, 4 -_`` 4t s `"---r TYPE 1 OIL WA TER SEPARA TOR , "''- 414 _ I*----.r _ STUB lE TYPE 1 RIM �8 -�403.5939sSEE DET141L..SL�L__C6 �-- :_�os4 ..-� 408.5 ► �./� � 3919-.50 398.,30 tB" DlA•< - 18" DfA � - _ _ ,�'�`` R/M TT T T 413.74- _ ii o 8r IE 0�9 8" lE-9- 4 ¢ 2 .Ip ... 3�`B3 398. �. .` N.E. 67Hlk S 3 UNDERGROUNDSERVICE �-- LOCATOR - - - - . - CALL BEFORE YOU 01G! 35L 4 1-800-424-5555 • T LF-B 4 LF d. , i ( f _ r _ h CB 12 I TYPE 1 I EXCA VA TE DITCH r 12 OUTFACE 15A ro ExrsnNc \� __..._402- •. I CHANNEL AND CLEAN 39/. 99 W `•` -- ExISnNG ( OUT EX/STING /E J2'' & 24" �96 5e 390,41 D F TYPE a - 48 I CHANNEL AS RIP-RAP - SEE DETAIL � Y 8 �,; 1 J / I ; 18" DIA. NEEDED. SHT. C6 I CB 11r512 - +o 6o0`� Es _ 406`-� 40 ,._._ lE 6" NEW 1&9 ` DI NE /2" I { �. �n� �� 9 ¢ I a„ �.�— � RIM IE jgo.9 394.0/ I STA 5+86.63, 9.54' RT — TYPE 1, THRU CURB G'RA TE L_ j CB 10 a � T � _ - � ' CB 5 } /0 1 M p I •V I � - 1 N y�tF 6" i - j �' STA 2+07, 18. 17' RT TYPE 2, 54" ' . -� SILO, ESM T ii i 11 OIL/WA TER - 1 i� 1� 21 TYPE 1 SEPARA TOR Z�,. — 3l0 8 .. �.zRIrN- ?..:. I i CpEo 3 L y_, lE 8,� 39 4 396-97 y 42L 3 YD 8E -LT 18 DIA. , IE 6 3��4 3910.98 » W \ _ o,03 7 1 RIM-49 4 05.45 » > i� 6 6"� - 4 3.00 (�►-s��� SCALE: 1 = 40 i 4 L0 - Qo 0 20 40 80 Qo 11 *6 Lou OU TFALL 10A T , z { 7 IE 12" �94':z9� 394.35 i s i-qt i t,. - Rl \�. ' TYPE2+97, RIP-RAP - SEE DETAIL It ! \ 1 W SHT. C6 / , 1 - r `. �,- 1 10' STORM DRA/NACE BIOFIL TRA TION SWALE—` 3t4. \ �� s L ' _ 1Dz G EASEMENT CONTOUR INTERVAL. SEE DETAILn H T C6 a I TWO FOOT CONTOUR INTERVAL ij = O.00, f "` f. / 1 6" STUB FOR KEYSTONE i I - ROCKERY DRAIN (TYP) Q _ VERTICAL L DATUM. v CITY OF RENTON VERTICAL DATUM (NGVD 1929) 7 0� YD' 8D BENCHMARK: Ol I i. 18 DIA. RIM-46L50 4o4.58 TOP ON MON. IN CASE, INTERSECTION OF 8 i \ t K IE 8"-49J� 4o2 .9/ (5) N.E. 4TH ST. AND UNION AVE. N.E. t�L� 2 lE 6" <�.-� 40Z �9T(nl 4�) = E 0 t ELEV. 397.77 (THE ORCHARDS)( OS) r•'� STA 8+50, 18.54' RT. I'' % % ,1 ~ 397.40 (EAST RENTON INTERCEPTOR I TYP,E 1, THRU CURB GRA; PROJECT PLANS BY RH2) OUTFALL 1A ' , 9 i 6, Ov . ,. 40,3 8 . ►C 6' NOTE: p '� w Al2, CONTOUR, BOUNDARY AND TOPOGRAPHIC o r I IE 12" zn 994.77 �, �O 93.3 . __.. L OCA TE ��` 25.8 RT. INFORMATION SHOWN HEREON BASED ON O RIP-RAP - SEE DETAIL � � TYPE 1 TOPOGRAPHIC SURVEY PREPARED BY TRIAD I ' SHT. C6 310FIL TRA T101V SWALE p R, \ 91 o ' 23 it SEE' DETAIL SaHT. 0-6 -�- f 00 ASSOCIATES, DATED 4-7-81. _ I C) ' � s� � o CB 1 - � . ESM r ,' �`, z ------ TYPE 2, 54" 1 -. D E T ^ 12 _ h ` �O �;•F` I �w, 0/L/WA TER /" 39.7 SEPARA TOR SEE DETAIL gib/ 2" CPE1 : _ w 2 y _ SH 1: C6 �/ , _._ 1 NOTE. SEE SHEET C5 FOR FSS�I:. DRA/N PROFILES / ' Z3• orva� a - A.0" CONSTRUCTED / LJ t7(.i _. A DaP�: 9� 18" DIA. SEE SHEET C6 FOR BY: Dry 4 8 s12 1 RIM - 2 399 8 q 7 I 10 IE 8" 336 9�1 STORM DRA/NA GE 3 8.Z2 DODDS ENGINEERS,EERS INC. I _— 12„ DETAILS O \ CIVIL ENGINEERING SURVEYING PLANNING \ 5LF L r: STUB - AVE. N.E.- SUITE 200 i HINGTON 98007 4205 148TH AVE :: ; r f �. 11 \ J! fa BELLEVUE WAS r: 4 ^� rn�,' 79/ ' - �� :� N [206 885 87877 FAX [206] 85-7963 - � 5119 z o`� / CB 8B _ TYPE 1 . . i t / D E i PROJECT NO 95127 -z2399 3-3 t • j RIM � � zn 2 n.� ` -- I lE r& 12" �-�-� 397.20 /9 3 743 — ---- I / - -- --- , I I = S/ { 1 PER CITY REVIEW 412JI97 - - - - - - . i - / NO REVISION BY APPR DATE ' 08 . ! Aq► t I j OF RENTON r 4 RlM � 9 CITY _ _ _ 12 �+[�VfE - -- 400 . T - - /E �96'--85 - __.._ . - `' �R A PPR t ��- �L DEPARTMENT OF PUBLIC WORKS N88�07', 5w g —= BLUEBERRY LANE 42' 606.01 ' Y I)ATIRAI s CB 9 { aY s uSTORM DRA /NA GE` PL A N CBCB CB am DESIGN D DATE MAR. 1997 FILE NO. s TYPE 1 STA TYPE91 36, 9. 17' RT STA TYPEI +77, 9. 17' RT TYPE 1 DRAWN `�^-- ^T ~ SCALE 1"=40 FIELD BOOK PAGE gifts��� - n CHECKED E. T. 03 / - APPROVED SHEET C4 OF 13 DIRECTOR OF PUBLIC WORKS