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Home My WebLink AboutSWP272856(1) BRIERE CREEK Renton, Washington Level II Drainage Analysis Prepared For: b 1.—! 0� Briere Enterprises u-1Y OF S Prepared By: Pacific Engineering Design, Inc. September 3, 1999 PEDI Job No. 99043 TECHNICAL INFORMATION REPORT BRIERE CREEK RENTON, WASHINGTON September 3, 1999 PREPARED FOR BRIERE ENTERPRISES 1944 Duvall Avenue NE Renton, WA 98059 (425) 228-7170 PREPARED BY PACIFIC ENGINEERING DESIGN, INC. 4800 S. 188T" STREET, SUITE 360 SEATTLE, WASHINGTON 98188 (206) 431-7970 IVA rsr�� Sf4NAL� [. TABLE OF CONTENTS I. Project Narrative................................. II. Drainage Report.................................. III. Level II Off-Site Analysis....................... IV. Briere Plat Supplemental Report............. I. Project Narrative II. Drainage Report III. Level II Off-Site Analysis I. PROJECT NARRATIVE Proiect Narrative — Briere Creek Preliminary Plat The Briere Creek Preliminary Plat is located on a parcel of land encompassing 3.68± acres of land approximately 300 feet north of the intersection of NE 18th St. and Duvall Ave NE on the east side of Duvall, directely across from the entrance to the May Creek Highlands development. The Brieres live in the existing residence located on proposed lot 1, and run their construction business from the existing residence located on proposed lot 18. Also located on the site is a large workshop, detached garage and storage shed. Numerous items from the Briers construction business are stored about the site. The site is zoned Residential - 8 Dwelling units per acre (R-8). The surrounding properties consist of single family to the north, the Plat of Summerwind to the east, a vacant lot to the south and single family homes on large lots to the west (May Creek Highlands). The vacant lot to the south is being developed by Williams brother Gerald Briere. The project is known as Briere Plat (City of Renton Permit No. C990249). At the writing of this narrative, construction drawings are being completed by Pacific Engineering Design, Inc. It is anticipated that approval will be granted by the City in September 1999. The site is mostly open in the front 1/3 and back 1/3 with a band of many small to medium size trees located in the middle 1/3. The site slopes off into a green belt tract on the east that also serves to convey storm runoff from a Summerwind division to the northeast to a regional detention pond to the southeast. The east property line is covered with thick brush and scattered small to medium size trees. The parcel slopes gently to the north and east and the present drainage pattern consists of sheet flow. Soils on site have been classified by the Soil Conservation Service as Alderwood Series (AgC) slopes of 0- 5% and Hydrologic Group C. A majority of the existing trees on site will be removed in preparation for construction of the plat infrastructure. The proposal is to subdivide the parcel through the platting process into 18 single-family residential lots with a public street and utilities serving each of the new lots. Building structure. Offsite improvements will consist of dedicating 12' of property along Duvall Ave NE for roadway widening and installation of new curbs, gutters and sidewalks. Utility lines consisting of franchised utilities (power, gas, telephone and cable T.V.), along with sanitary sewer, water mains and storm drainage will also be extended as necessary to serve this development. The estimated plat construction cost is $400,000 and the estimated fair market value of the 18 finished lots is $1,080,000. These numbers are only estimates at this time and are subject to revision. Due to the nature of the site the installation of the road and utility infrastructure will involve minimal excavation and embankments. At this time it is estimated the quantity of material in fills or excavation will be less than 1000 c.y. Additional yard fills may be needed when homes are constructed on each lot; however, the actual building plans have not been finalized so the amount of yard fill, if any, cannot be assessed. This will be a part of the building permit submitted at a later date. The portion of the site containing the public road and utilities will be dedicated to the City of Renton through the platting process, as public property. Utility lines across lots/private property will be within easements. II. DRAINAGE REPORT PACIFIC ENOINEERINO DESIQN INC. JOB cree k CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF 9 CALCULATED BY "[• L�//DATE 0, 7 6, 40 . . ... . 2 � 2 �- Of .. 57 xi zl ................................ 30 z� z� x s S . .. . -_ I59_b ll_d 5 - /D1.5 l3o I 22 �' -+ -_ _ . �� ._ .� . .. ,Pi o = ............2,9.... .. ._ 9.5 ,Br�ere CreeK 90� PACIFIC ENQINEERINQ DESIQN INC. roe x CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF CALCULATED BY �/ / DATE < ..... y O , ve>�y1h re Cr ' . .... , ✓Y/deb y �— . .. . -� �'ZX �U 2� ZSU ate,._. . . . 2 --at� i ose�S' 4y c�' >��X 2 . ..�- a x 43 - 4 /6 .................. a... .. »ve. ► -�-_: 7x �� : - --. .� �1' - - x ....z�. D .. g 3, -' 1. l0 Z D,/D'� -4 6Q............ ........... .... ......... . ...... ..... .. ....... . . . . �! c //. ..... PACIFIC ENQINEERiNQ DEsiQN INC. roe goerP C✓wk- - » �3 CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF CALCULATED BY r/�H DATE .... Vie/ Ag e g , r✓�d cis 61io P y ,I C c . ..... c �ros - a5"2 9 G G . .. 3 n�r-�r-� r. � ��T� T � nTr �rr-: r-r_ nT-Ti •— n c-•i din ir��-r+,� ��ocr �r�C`.1,^,—,n —>r�—>r� r n.�.•,if•-i•• -�r-,-�c t •.�,- - , � � `�' � � sue` .-- _ III. LEVEL II OFF-SITE ANALYSIS Lo �0, PACIFIC ENQINEERINQ DESIQN INC. CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF CALCULATED BY DATE / ,t _D . . a,►-r �i (.eve/ o�/�-�scd��i q hGf• ��s ....... ._.... �.. Yli /✓Nf✓tfa ` ,(�!( ...... �!/C1[�Y1 ,Y"1 7i�/-5.. �Hk�S..�S ... 1 _._ . . .... .: . . : . .. : .t .. f � �« i �� e 57ruu�� MdA i -jam/due . �ii� . �/l / / / is �-f �c� �a,�tC� `_ G -2 �1 e � — ✓ '�/d .... (Jr y............ U Gam- r o -5 r1 C o►.✓ Antis 4 /7 !n �e lee ....... ..... off- �e �y��ih 1 ... ............... .. .. .. 1, i., ► .!', i �_, I _� ^ � _ x 1 ........................... L ,y�r Cov�/r� 1/ Dd . .. u . . l VIP 4Rnn RR-T'F-1 —,T RI IITF c r=/1TTI F c-:IR'I MR FAX/,l---I'1_-7C1-� PACIFIC ENQINEERINQ DESIGN INC. 'roe Y " CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF CALCULATED BY DATE ........................ S�X ........................ D wa _ �//r /�-! ...... . u e5 0-7 _ J _ o►-2. .............3.......... 4_ tJ rtcC � P.✓ i. v w Zv��../l .. / /fit . DkiHS G�* C �' , cl+del �i sq S i ............._...h%i � pwi 40 L ..... ll Tr, k fir` "? _ �f' r�tic P� Gl�jatiP) 'r . ,eve 7v � ioo .1D-e •3o _c T �Sfow . wlll ca 1Gt, KS /�,� k. '/ / 8/10/99 4 : 40 : 26 pm Pacific Engineering Design Inc page 1 BRIERE CREEK PLAT ADDITIONS TO LEVEL II DOWNSTREAM ANALYSIS - JOB NO. 99043 --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN SUMMARY BASIN ID: BRIERE NAME : OFF-SITE 100-YR. DEV. FLOW SBUH METHODOLOGY TOTAL AREA. . . . . . . : 2 . 28 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 95 inches AREA. . : 1 . 18 Acres 1 . 10 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 98 . 00 TC. . . . . 5 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 PEAK RATE : 1 . 95 cfs VOL: 0 . 59 Ac-ft TIME : 470 min BASIN ID: DEV100 NAME : 100-YR. DEVELOPED - SITE SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 76 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 95 inches AREA. . : 1 . 95 Acres 1 . 81 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 98 . 00 TC. . . . . 5 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE : 3 . 22 cfs VOL: 0 . 97 Ac-ft TIME : 470 min BASIN ID : OFF-100 NAME : OFF-SITE 100-YR. EX. TO CULV. SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 77 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 95 inches AREA. . : 3 . 53 Acres 0 . 24 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 85 . 00 98 . 00 TC. . . . : 37 . 01 min 37 . 01 min ABSTRACTION COEFF : 0 . 20 TcReach - Sheet L: 300 . 00 ns : 0 . 1500 p2yr: 2 . 10 s : 0 . 0164 TcReach - Shallow L: 200 . 00 ks : 11 . 00 s : 0 . 0180 TcReach - Channel L : 410 . 00 kc : 20 . 00 s : 0 . 0113 PEAK RATE : 1 . 54 cfs VOL: 0 . 78 Ac-ft TIME: 480 min BASIN ID : SUMMER NAME: 100-YR. DEV. FLOW - SUMMERWIND SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4 . 69 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 95 inches AREA. . : 2 . 58 Acres 2 . 11 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 98 . 00 TC. . . . : 10 . 00 min 10 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE : 3 . 59 cfs VOL : 1 . 19 Ac-ft TIME: 480 min MAN-MADE CHANNELS VARIABLES LIST : Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y, Q, B,M, S OR N) ? Y Q (CFS) ? 10 . 30 RESULTS B (FT) ? 8 M (FT/FT) ? 3 Y= 0 . 39 FT S (FT/FT) ? . 014 A= 3 . 59 SF N (FT^1/6) ? . 030 P= 10 . 47 FT V= 2 . 87 FPS F= 0 . 86 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- ►'Qr�1QG �. �� u �aE; STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN Figure III-2. 14 - Headwater Depth for Smooth Interior Pipe Culverts With Inlet Control 60 - 10,000 168 8,000 EXAMPLE ( 1 ) (2) (3) '— 156 `— 6,000 �•42 �^cn•, IS S feet) 6. ENTRANCE TYPE T� PE 144 - 5.000 Q-120 cfs -----_-_ S SQUARE EDGE WITH - 4,000 ,w• ,w 6 5 HEADWALL r 132 D feet �- 3,000 4. :- 120 ('1 2.5 e.e S. a , - 2,000 12) 2.1 7 s 1 I 108 i 1}1 2.2 7.7 4 C 3. 1 , n feet 3 1- 36 1,000 3 PLAN - 800 GROOVE END WITH ea - -- - HEADWALL i 600 2 r 500 - 400 / ti 2. - LO 300 z z 60 u 200 / LS-- --- — ~ PLAN 54 GROOVE END I^ o PROJECTING w 48 / w _ 100 U / cr 80 z J C 42 60 a - 0 1 1.0 1. w N S O L.1 —, i 0 o HW ENTRANCE ¢ - 40 SCALE, TYPE ac 1.0 � 36 w w 30 (lV Sgyore edge .r1h R .9 .9 <Q 33 % n.oe.on 3 .9 / p p — 20 / (2) Groot• end .ern Q w / 131 Groo.e end •8 "") 27 _ Droj.cl.np 10 c( = 8 7 7- - 24 - — — 6 To ems. scar• 121 or I31 or o,.ct J 21 5 noritontau7 10 'Cole (11,then f j 4 ems. ilra-ght reclined line through I J and 0 ,Cole.,or ....r'. e. I_ 3 �IUUroHd, 1 8 _ .6 - - _ a 2 i 15 1.0 5 5 5 (2 III-2-34 FEBRUARY, 1992 CULVERTS RESULTS DIAMETER (IN) ? 18 HEADWATER (FT) FLOWRATE (CFS) LENGTH (FT) ? 71 411 . 90 OC 5 . 37 FRICTION COEFF (FT-1/6) ? . 013 412 . 40 OC 8 . 05 ENT+EXIT COEFF ? 1 . 5 412 . 90 OC 10 . 04 INLET CONTROL COEFF ? 0 . 62 413 . 40 OC 11 . 69��2,C�� 413 . 90 OC 13 . 14 INV ELEV OUT (FT) ? 410 . 00 414 . 40 OC 14 . 45 INV ELEV IN (FT) ? 410 . 40 414 . 90 OC 15 . 64 TAILWATER ELEV (FT) ? 411 . 50 415 . 40 OC 16 . 75 ELEV INCREMENT (FT) ? 0 . 5 415 . 90 OC 17 . 80 416 . 40 OC 18 . 78 416 . 90 OC 19 . 71 417 . 40 OC 20 . 61 417 . 90 OC 21 . 46 418 . 40 OC 22 . 29 418 . 90 uc 23 . 08 419 . 40 OC 23 . 85 <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN Table III-1.3 SCS Western Washington Runoff Curve Numbers (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type lA rainfall distribution, 24-hour storm duration. LAND USE DESCRIPTION CURVE NUMBERS BY HYDROLOGIC SOIL GROUP A B C D Cultivated land(1) : winter condition 86 91 94 95 Mountain open areas: low growing brush & 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 8� 86 Orchard: with cover crop- 81 88 92 94 Open spaces, lawns, parks, golf courses, cemeteries, landscaping. Good condition: grass cover on Z75% of the 68 80 86 90 area Fair condition: grasp cover on 50--75% of 77 85 90 92 the area Gravel roads & parking lots: 76 85 89 91 Dirt roads & 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) Separate curve number 1.0 DU/GA 15 shall be selected for 1.5 DU/GA 20 pervious & impervious 2.0 DU/GA 25 portions of the site 2.5 DU/GA 30 or basin 3.0 DU/GA 34 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 PUD's, condos, apartments, %impervious commercial businesses & must be industrial areas computed (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Sec. 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. III-1-12 FEBRUARY, 1992 IV. BRIERE PLAT SUPPLEMENTAL REPORT LEVEL II DRAINAGE ANALYSIS BRIERE PLAT KING COUNTY, WASHINGTON December 18, 1998 PREPARED FOR J. BRIERE CONSTRUCTION 23205 SE 192ND STREET MAPLE VALLEY, WA 98038 (425) 432-7582 PREPARED BY PACIFIC ENGINEERING DESIGN, INC. 130 ANDOVER PARK EAST, SUITE 300 SEATTLE, WASHINGTON 98188 (206) 431-7970 R. NEwF Q Z 12701 /STER��`� sIONA l EXPIRES: SEPT. 5, 1999 TABLE OF CONTENTS I. PROJECT NARRATIVE............................................................................................ H. DRAINAGE REPORT................................................................................................ III. LEVEL II OFFSITE ANALYSIS................................................................................. EXISTING CONDITIONS.................................................................................................. DEVELOPEDCONDITIONS ............................................................................................. IV. .................................................................................................................................. V. .................................................................................................................................. VI. .................................................................................................................................. VII. .................................................................................................................................. I. PROJECT NARRATIVE Proiect Narrative_..Briere Preliminary Plat The Briere Preliminary Plat is located on a parcel of land encompassing 2.28f acres of land approximately 170 feet east of the NE 18th St./Duvall Ave NE intersection. The site is vacant except for an encroaching carport and two small sheds and is zoned Residential - 8 Dwelling units per acre (R-8). The surrounding properties consist of vacant property to the north, Plat of Summerwind to the east, Parkway Townhomes (condominiums) on the south and single family homes on large lots to the west. The site is mostly cleared with some small trees and brush adjacent to the exterior property lines on the south and east with the remainder of the site in pasture grasses. The parcel slopes gently to the north and east and the present drainage pattern consists of sheet flow. Soils on site have been classified by the Soil Conservation Service as Alderwood Series (AgQ slopes of 0-5% and Hydrologic Group C. No trees removal is being proposed for construction of the plat infrastructure. , The proposal is to subdivide the parcel through the platting process into 12 single-family residential lots with a public street and utilities serving each of the new lots. Building height will be limited to two stories - 30' dwellings and 15' for detached accessory structure. Offsite improvements will consist of additional pavement, curbs, gutters, and sidewalks along the existing NE 18th St. from the parcel to the intersection of NE 18th St. with Duvall Ave NE. Utility lines consisting of franchised utilities (power, gas, telephone and cable T.V.), sanitary sewer, water mains and storm drainage will also be extended within the present NE 18th St. corridor to serve this development. In addition a drainage easement for the bioswale connecting the proposed vault outfall to the offsite drainage corridor in Summerwind is being proposed across offsite property to the north. The owner of this property has been consulted regarding this easement and has tentatively agreed to grant it. The estimated plat construction cost is $360,000 and the estimated fair market value of the 12 finished lots is $720,000. These numbers are only estimates at this time and are subject to revision. Due to the nature of the site the installation of the road and utility infrastructure will involve minimum excavation and embankments. At this time it is estimated the quality of material in fills or excavation will be less than 500 c.y. Additional yard fills may be needed when homes are constructed on each lot; however, the actual building plans have not been finalized so the amount of yard fill, if any, cannot be assessed. This will be a part of the building permit submitted at a later date. The portion of the site containing the public road and utilities will be dedicated to the City of Renton through the platting process, as public property. Utility lines across lots/private property will be within easements. II. DRAINAGE REPORT DRAINAGE REPORT The site is comprised of 2.28 acres of land near Duvall Avenue NE and NE 18th Street in Renton, Washington. Except for two sheds and an encroaching carport, the site is vacant with some scattered trees and brush. The projects consists of off-site utility and roadway improvements to NE 18th Street and construction of onsite plat improvements which include sanitary sewer, storm drainage, water facilities, street pavement, street lighting, detention vault and a water quality biofiltration swale. After construction of roads and utilities the parcel will be subdivided in 12 lots. Drainage flows are generally directed towards the northeast into an existing off-site drainage course flowing southerly into Tract "A" of the Summerwind Div. 4 Plat. The open drainage course discharges into a piped conveyance system flowing south under Field Avenue NE. The project will comply with Core Requirements 1-5. None of the Special Requirements 1-12 appear to apply to this project. Preliminary drainage calculations to size a storm drainage detention vault were done based on the SBLM hydrograph method. Adjusting for a small by-pass area, the pre-developed 2, 10 and 100- year/24 hr. storm events were matched with the post-developed 2, 10 and 100-year/24 hr. events to determine the required storm detention vault volume (see attached calculations). Preliminary biofiltration swale calculations were done based on the 2-year/24 hr. pre-developed discharge rate (see attached calculations). A wetpond is not required on this project due to the traveled impervious area being less than 1 acre. O� If i t'•of � 1 N . -. �_� .. . sue_._-�-. � ,- . a t .�mo •.,, ,,`,. Existing Rates: = (Ex. - Bypass) + (Ex Bypass) 2 yr. (existing) =0.263 + 0.008 = 0.271 cfs 10 yr. (existing) =0.531 + 0.015 = 0.546 cfs 100 yr. (existing) = 0.888 + 0.025 = 0.913 cfs Release Rates = (Ex - Bypass) + (Ex Bypass) - Bypass Release 2 yr. (Dev) = 0.271 - 0.020 = 0.251 cfs 10 yr. (Dev) = 0.546 - 0.029 = 0.517 cfs 100 yr. (Dev) = 0.913 - 0.039 =0.874 cfs III. LEVEL 11 OFF-SITE ANALYSIS The bioswale from the proposed Briere plat runs approximately 140' north of the property line where it combines with open channel flows from the Summerwind Div. 4 plat detention vault. This open channel was surveyed by Triad Associates and shows it has a length of approximately 300' at an average slope of 1.4%. At the end of the open channel is a 12" dia. intake pipe which connects the channel to a large drainage structure (10' long x 3' wide) containing a spillway and trash screen. An 18" diameter pipe carries flows from the structure to Type II SDMH Basin in Field Avenue NE and thence into a storm detention pond constructed as part of the Summerwind development. A preliminary check of the downstream channel and pipe capacity assuming a worst case which would be the 100-year storm event with failure occurring at the existing Summerwind detention vault and the proposed Briere plat vault. The drainage flows are: • Q = 12.20 cfs from Summerwind vault based on 21" diameter pipe outfall at 0.51% slope flowing full (detention failure) • Q = 1.92 cfs from Briere Plat with full development (detention failure) • Q = 3.09 cfs from 7.53+ acre drainage basin north of proposal assuming existing conditions The total flow at the downstream spillway structure is estimated as 12.20 + 1.92 + 3.09 = 17.21± cfs. Using King County Figure 4.3.5c an 18" diameter culvert would require a Hw/D = 3.2' for a Type 1 entrance or a Hw = 3.2 x 1.5 = 4.8'. From the Basin Map we estimate the road Field Avenue NE is at least 4.8' above the culvert invert. It is possible that Field Avenue NE could overtop in this area; however, the likelihood of simultaneous full failure of both vaults during the 100-year event is very unlikely. Preliminary calculations checking the open channel capacity showed the water depth at 17.2 cfs would be about 0.53' and have a channel velocity of 3.4's. I. Existing Conditions Total On-Site Area= 2.278 Acres Area of Road Right-of-Way = 0.494 Acres Tc 370 LF @ S = 1.216% CN - 85 (Meadow or Pasture) Bypass= 33 x 50 = 0.038 acres II. Developed Conditions Total On-Site Area= 2.278 Ac Bypass = 0.038 Acres - Impervious P2 = 2.10 in. P10 = 2.95 in. 2.278 = 0.038 =2.240 Acres P 100= 3.95 in. Grass = 1.162 Ac CN = 86 Roadways = 0.456 Ac CN= 98 Homes = 0.622 Ac CN = 98 2.240 Ac Total Existing 2 yr. - 0.263 + 0.008 =0.271 cfs 10 yr. - 0.531 + 0.015 =0.546 cfs 100 yr. - 0.888 + 0.025 = 0.913 cfs Allowable Release Rates= 2 yr. - 0.271 - 0.020= 0.251 cfs 10 yr. - 0.546 - 0.029= 0.517 cfs 100 yr. - 0.913 - 0.039= 0.874 cfs 12/4/98 10 : 19 : 41 am Pacific Engineering Design Inc BRIERE PLAT - J08 NO .98016 DRAINAGE CALCULATIONS ===================================================================~ BASIN SUMMARY BASIN ID: DEV100 NAME : 100-YR ' DEV LESS BYPASS S8UH METHODOLOGY TOTAL AREA ' ' ' . ' ' ' : 2 '24 Acres BA5EFLOWS; O 'OO cfs RAINFALL TYPE ' ' ' . KC24HR PERV IMP PRECIPZTATIDN . ' ' ' ; 3 '96 inches AREA . . : 1 . 16 Acres 1 .08 Ac TIME INTERVAL ' ' ' ' 10 '00 min CN ' ' ' ' : 86 '00 98 .00 TC ' ' . ' : 5 '00 min 5 '00 mir ABSTRACTZON C0EFF : 0 '20 PEAK RATE : 1 '92 ofa VOL : 0 '58 Ac-ft TIME : 470 min _ PACIFIC ENOINEEFUNQ DESIQN INC. Boa y✓/eY�i ' /�// / % • CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF 7� CALCULATED BY ✓Y(%�/2 DATE ................:.. k°.. .. . 1J X .. - . .� jC_S"v.. ..-� Zo x.3 4 f 3 e .3 ..�.1P X v ............ ...........j..........:....... ..... ..... ... ...... ...... ... ... .. ... .. .... .._.. .... e i .._................_ ..... �. X ¢� x3e � a ....... .... ... 3.ax. .... .e. ........... _.... ........................... ... f..G tfv �D v . 2�o v - �3 .. l .�- 3ooa d ..... ..... : : .» �.� sr ._C �'. . ....._......... 9 }c .✓ r........_ .... PAS .... .. 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Zy 3.......................... .................................... ........... ........... .......... . .................... ..... ......... :... .............. .......... ..................................... ........................................ .............__. .... ...... .... ... ? . 5 Z �.... / .. 3, ze /, fro l— t ..... ............... .................... ...... .... ...... ..... ...... ...... ...... ..... . ..... ........ �h� zs L . . ......._....._ ............. ..... .... .... . .� y. ...X.. ..... r .... .... ... » v .............. 130 ANDOVER PARK EAST, SUITE 300 SEATTLE, WASHINGTON 98188 (206) 431-7970 FAX:431-7975 12/4/98 10 : 17 : 30 am Pacific Engineering Design Inc pa--pe BRIERE PLAT - JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: OFF-100 NAME : OFF-SITE 100-YR . EX . TO CULV . SBUH METHODOLOGY TOTAL AREA . . . . . . . : 7 .53 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 3 .95 inches AREA . . : 7 . 17 Acres 0 .36 Ac TIME INTERVAL . . . . 10 .00 min CN . . . . : 85 .25 98 .00 TC . . . . : 37 .01 min 37 .01 ABSTRACTION COEFF : 0 .20 TcReach - Sheet L : 300 .00 ns :0 . 1500 p2yr : 2 . 10 s :0 .0164 TcReach - Shallow L : 200 .00 ks: 11 .00 s: 0 .0180 TcReach - Channel L : 410 .00 kc : 20 .00 s : 0 .0113 PEAK RATE : 3 .09 cfs VOL : 1 .57 Ac-ft TIME : 480 min PACIFIC ENGkINEERINO IDESIGN INC. ✓60 CIVIL ENGINEERING AND PLANNING CONSULTANTS SHEET NO. OF CALCULATED BY DATE )9, v .......... 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Elev: 413 .10 ft Orifice 2 Diameter : 2 .2000 in . Elev : 414 .40 ft Orifice 3 Diameter : 2 .7900 in . STAGE (--DISCHARGE---) STAGE (--DISCHARGE---) STAGE (--DISCHARGE---) STAGE (--DISCHARGE---) (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- ------------------ 411.48 0.0000 412.70 0.1354 414.00 0.3191 415.30 0.6347 411.50 0.0173 412.80 0.1408 414.10 0.3297 415.40 0.6530 411.60 0.0424 412.90 0.1460 414.20 0.3399 415.50 0.6707 411.70 0.0575 413.00 0.1511 414.30 0.3497 415.60 0.6878 411.80 0.0693 413.10 0.1560 414.40 0.3592 415.70 0.7044 411.90 0.0794 413.20 0.2022 414.50 0.4352 415.80 0.7205 412.00 0.0884 413.30 0.2241 414.60 0.4718 415.90 0.7361 412.10 0.0965 413.40 0.2417 414.70 0.5017 416.00 0.7514 412.20 0.1040 413.50 0.2572 414.80 0.5281 416.10 0.7663 412.30 0.1110 413.60 0.2713 414.90 0.5522 416.20 0.7809 412.40 0.1175 413.70 0.2843 415.00 0.5746 416.23 0.7852 412.50 0.1238 413.80 0.2965 415.10 0.5956 412.60 0.1297 413.90 0.3081 415.20 0.6156 12/4/98 I0 : 28 : 16 am Pacific Engineering Design Inc page BRZERE PLAT - JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: SUMMER NAME : 100-YR ' DEV ' FLOW - SUMMERWIND 5BUH METHODOLOGY TOTAL AREA . ' ' . ' . . : 4 '69 Acres BASEFLOWS : 0 '00 ofo RAINFALL TYPE ' ' ' ' : KC24HR PERV IMP PRECIPITATION ' ' ' ' : 3 '95 inches AREA . . : 2 '58 Acres 2 ' 11 Ac TIME INTERVAL . ' ' . : 10 '00 min CN ' ' ' ' : 86 '00 98 .00 TC ' ' ' ' : 10 .00 min 10 '00 mlr ABSTRACTION COEFF : 0 '20 PEAK RATE : 3 '59 ofa VOL : 1 '19 Ac-ft TIME : 480 min A-1 t414100 . MAN-MADE CHANNELS VARIABLES LIST: Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y, Q, B,M, S OR N) ? Y Q (CFS) ? 17 . 21 RESULTS B (FT) ? 8 M (FT/FT) ? 3 Y= 0 . 53 FT S (FT/FT) ? . 014 A= 5. 04 SF N (FT A1/6) ? . 030 P= 11 . 33 FT V= 3 . 42 FPS F= 0 . 90 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- �o� ►� POW4.4 P� � �� K� � C�Uu ►-Sc CULVERTS RESULT'S DIAMETER (IN) ? 18 HEADWATER (FT) FLOWRATE (CFS) LENGTH (FT) ? 100 102.50 IC 7.61 FRICTION COEFF (FT^1/6) ? .013 103.00 IC 9.83 ENT+EXIT COEFF ? 0.5 103.50 IC 11.63 INLET CONTROL COEFF ? 0.62 104.00 IC 13.19 104.50 IC 14.58 INV ELEV OUT (FT) ? 100.00 105.00 IC 15.85 INV ELEV IN (FT) ? 101.00 105.50 IC 17.03 TAILWATER ELEV (FT) ? 101.00 106.00 IC 18.13 ELEV INCREMENT (FT) ? 0.5 106.50 IC 19.16 107.00 IC 20.15 107.50 IC 21.00 108.00 IC 21.98 108.50 IC 22.84 109.00 IC 23.67 109.50 IC 24.48 110.00 IC 25.25 <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- } 71� kk\,k k`kkkkkk\k` kk\;\ki\.\`k,:,\"�kki;;.,`:tiikSkk kk,\`•:`k"\\�?,\�k\',�` \`?,`,\U`, `k'�`\k\„`C2\kk ,;:\.'?k`,�`\k`„\`d`. ;ik k`�kk:?`? 2;k?kkkkz�' i��.,,,kzkkz4zz kLi; \,,,,,,,»:.;k kkkkkk��`,�? .,,,,,,k,\`kk�•,;k?`k;k',kk�,\��,�"",,.;.,kkk:.,,»»,,,,,kk,„\»�?„,�„U�xkkkkk,,»,`C`:k,\`k:::,`.:,.,:»�k�kkkk'.kkkkk:kkkk:,tv",k,\�,`2,k*��k�'. » m A CCI LVERT S RESULTS DIPMETER (IN) ? 13 HEADWATER (FT) FLOWRATE (CFS) LENGTH (FT) ? 100 - ------------------------------ 102. 50 IC 6. 14 FRICTION COEFF (FT-1/6) 2 . U12' 102. 70 IC 6. 91 ENT+EX.IT COEFF ? 5 1.02. 90 IC 7. 60 INLET CONTROL COEFF ? . 5 103. 10 IC 8 . 24 103. 30 IC 8 . 83 INV ELEV OUT (FT) ? 10o 103. 50 Ir 9. 38 INV ELEV IN (FT) ? 1.01 103. 70 IC 9. 90 TAILWATER ELEV (FT) ? 101 103. 90 IC 10. 40 ELEV INCRFMENT (FT) ? . 2 104 . 10 IC 10. 87 104 . 30 IC 11. 32 104 . 50 IC 11. 76 104 . 70 IC 12. 18l2�31 104 . 90 IC 12. 58 105. 10 IC 12. 98 105. 30 IC 13. 36 105. 50 IC 13. 73 h.><, <Shift> SPrt Sc'.- print "Return> repe-It <Space Bar> back to menu I ------------------------------------------------------------------------------- I 104 SO Iu l _ _- _ -2 �� KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 4.3.5C HEADWATER DEPTH FOR SMOOTH INTERIOR PIPE CULVERTS WITH INLET CONTROL 180 10,000 168 8,000 EXAMPLE (2) (3)6. ENTRANCE TYPE 156 6,000 0.42 inches (3.5 feet) — 6-- SQUARE EDGE 11 H 0.120 cf s -- In T 144 5,000 6 5' S HEADWALL 4,000 HW* Hw 132 0 flat 4. 3,000 (1) 2.5 e.e 5' 4. 120 (2) 2.1 7.4 2,000 (3) 2.2 7.7 108 3. e0 in feet 3' 96 1,000 I 3. PLAN (1) GROOVE END WITH 800 / _ _ _ HEADWALL 84 500 2 0 i Q I N 72 400 / Lj U / () z 60 v 200 / 1.5 PLAN (2) ? (��'/ � GROOVE END 0 54 a PROJECTING 0 Cr 48 / 100 �/ U 4 2 U 60 (� �� Li 1.0 —A O o 50 HW SALE ENTRANCE O I.0 , Iz 40 0 TYPE w 1-- 36 30//� (1) Square edge .ilh Q m / head.all Q •9 C 33 a 2 0 (2) Groove end .to w 30 head.all 2 8 .8 (3) Groove and '8 27 projecting r 10 7 7- 24 8 .7 6 To use scale (2) or (3) project 21 5 horizontally to scale (1),then 4 use slralght inclined line through 0 and 0 scoles,or reverse as 6 3 illustrated. 6 .6 18 i 2 15 .5 .5 .5 1.0 -- — 12 Ow _ 2 = ITZ CFs D T4PE I 4.3.5-11 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1.2 CORE REQUIREMENTS The seven Core Requirements are; (1) Discharge at the Natural Location. The discharge from a proposed project site must occur at the natural location. (2) Off-Site Analysis. All proposed projects must identify the upstream tributary drainage area and perform a downstream analysis. Levels of analysis required depend on the problems identified or predicted. At a minimum, a Level 1 analysis must be submitted with the initial permit application. (3) Runoff Control. Proposed projects must provide runoff controls to limit the developed conditions peak rates of runoff to the pre-development peak rates for specific design storm events based on the runoff from defined existing site conditions, and install biofiltration measures. (4) Conveyance System. All conveyance systems for proposed projects must be analyzed, designed and constructed for existing tributary off-site runoff and developed on-site runoff from the proposed project. (5) Temporary Erosion and Sedimentation Control. All projects that require engineered drainage plans shall provide Temporary Erosion and Sedimentation Control (TESC) measures that minimize the transport of sediment to drainage facilities, water resources, and adjacent properties. (6) Maintenance and Operation. Maintenance of all drainage facilities constructed or modified by a proposed project is the responsibility of the property owner (see Maintenance Requirements for Privately Maintained Drainage Facilities in Appendix A), except King County may assume maintenance of drainage facilities constructed for formal Plat Subdivisions, planned unit developments, and some Short Plat Subdivisions two years after construction approval. (7) Bonds and Liability. All drainage facilities for proposed projects (except drainage stub-out connections, downspout roof drain infiltration systems and downspout dispersion systems for single-family residential lots) must be constructed in conformance with the bond and liability requirements of King County Code 9.04.100. 1.2-1 11/94 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1.3 SPECIAL REQUIREMENTS In addition to the seven Core Requirements, twelve Special Requirements may apply to a proposed project. Each set of requirements below Is preceded by the conditions in which the requirements apply its 'threshold." Most thresholds can be assessed and the special requirements determined in advance of formal engineering plan preparation. Other thresholds may require a special study before a determination can be made as to the application of a Special Requirement to a proposed project. The twelve Special Requirements are: (1) Critical Drainage Areas (2) Compliance with an Existing Master Drainage Plan (3) Conditions requiring a Master Drainage Plan (4) Adopted Basin or Community Plans (5) Special Water Quality Controls (6) Coalescing plate oil/water separators (i) Closed Depressions (8) Use of Lakes, Wetlands or Closed Depressions for Runoff Control (9) Delineation of the 100 year Floodplain. (10) Flood Protection Facilities for Type 1 and Type 2 Streams (11) Geotechnical Analysis and Report (12) Soils Analysis and Report 1.3 1 1/90 6/30/99 3 : 7 :49 pm Pacific Engineering Design Inc page 1 BRIERE PLAT - JOB NO. 98016 DRAINAGE CALCULATIONS STAGE STORAGE TABLE RECTANGULAR VAULT ID No. 1 Description: UNDERGROUND VAULT Length: 52 . 00 ft . Width: 30 . 00 ft . voids : 1 . 000 STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --AC-Ft- (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --Ac-Ft- ........................................................................................................ 415.83 0.0000 0.0000 417.00 1825 0.0419 418.20 3697 0.0849 419.40 5569 0.1279 415.90 109.20 0.0025 417.10 1981 0.0455 418.30 3853 0.0885 419.50 5725 0.1314 416.00 265.20 0.0061 417.20 2137 0.0491 418.40 4009 0.0920 419.60 5881 0.1350 416.10 421.20 0.0097 417.30 2293 0.0526 418.50 4165 0.0956 419.70 6037 0.1386 416.20 577.20 0.0133 417.40 2449 0.0562 418.60 4321 0.0992 419.80 6193 0.1422 416.30 733.20 0.0168 417.50 2605 0.0598 418.70 4477 0.1028 419.90 6349 0.1458 416.40 889.20 0.0204 417.60 2761 0.0634 418.80 4633 0.1064 420.00 6505 0.1493 416.50 1045 0.0240 417.70 2917 0.0670 418.90 4789 0.1099 420.10 6661 0.1529 416.60 1201 0.0276 417.80 3073 0.0706 419.00 4945 0.1135 420.20 6817 0.1565 416.70 1357 0.0312 417.90 3229 0.0741 419.10 5101 0.1171 420.30 6973 0.1601 416.80 1513 0.0347 418.00 3385 0.0777 419.20 5257 0.1207 420.40 7129 0.1637 416.90 1669 0.0383 418.10 3541 0.0813 419.30 5413 0.1243 420.50 7285 0.1672 6/30/99 3 : 7 : 49 pm Pacific Engineering Design Inc page 2 BRIERE PLAT - JOB NO. 98016 DRAINAGE CALCULATIONS STAGE DISCHARGE TABLE MULTIPLE ORIFICE ID No. 1 Description: ORIFICE DISCHARGE ASSEMBLY Outlet Elev: 415 . 83 Elev: 413 . 83 ft Orifice Diameter: 2 . 9443 in. Elev: 417 . 03 ft Orifice 2 Diameter: 3 . 0234 in. Elev: 417 . 73 ft Orifice 3 Diameter : 2 . 8828 in. STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> (ft) ---CfS-- ------- (ft) ---CfS-- ------- (ft) ---CfS-- ------- (ft) ---CfS-- ------- ........................................................................................................ 415.83 0.0000 416.50 0.1926 417.20 0.3776 417.90 0.6628 415.90 0.0622 416.60 0.2064 417.30 0.4141 418.00 0.7081 416.00 0.0970 416.70 0.2194 417.40 0.4457 418.10 0.7482 416.10 0.1222 416.80 0.2317 417.50 0.4741 418.20 0.7851 416.20 0.1431 416.90 0.2433 417.60 0.5003 418.30 0.8196 416.30 0.1613 417.00 0.2545 417.70 0.5248 418.40 0.8521 416.40 0.1776 417.10 0.3307 417.80 0.6075 418.50 0.8831 6/30/99 3 : 7 : 53 pm Pacific Engineering Design Inc page 3 BRIERE PLAT - JOB NO. 98016 DRAINAGE CALCULATIONS LEVEL POOL TABLE SUMMARY MATCH INFLOW -STO- -DIS- <-PEAK-> OUTFLOW STORAGE <--------DESCRIPTION---------> (cfs) (cfs) --id- --id- <-STAGE, id (cfs) VOL (cf) ..................................................................................... 2-YR. ........ ................ 0.25 0.83 1 1 416.97 7 0.25 1776.15 cf 10-YR. ....................... 0.52 1.32 1 1 417.67 8 0.52 2867.02 cf 100.YR. . ..................... 0.87 1.92 1 1 418.47 9 0.87 4123.76 cf 10/27/98 11 :43 : 14 am Pacific Engineering Design Inc BRIERE PLAT - JOB NO .98016 DRAINAGE CALCULATIONS HYDROGRAPH SUMMARY PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min . cf\AcFt Acres --------------------------------------------- 1 0 .263 490 7067 cf 2 .24. � � ��( ___._ 2 0 .531 480 12573 cf 2 .24_1hcge_EX- _F3 PASS 3 0 .888 480 19622 cf 2 .24_ (00CtRr F.x. b�PASS 4 0 .829 470 11235 cf 2 .24 Z (L DEV -.$�?A,;S .._ 5 1 .318 470 17470 cf 2 .2ej 6 1 .917 470 2SO88 cf 2 .24 IU-) Q D r�--V _gj�'ASS_._ 7 0 .251 540 11235 cf 2 24 2�-te Qou gi p. 8 O .517 510 17470 cf 2 9 0 .874 500 25088 cf 2 .24 .jQ0 Lj V— -�)0(ATED 11 0 .008 480 120 cf 0 .04__ _Z12 F_K TPASS 12 0 .015 470 213 cf 0 .04 qp1 _EX' t7LjphSS 13 0 .025 470 333 cf 0 .04l(�tl� F , , pi.[Pa�S 14 0 .020 470 258 cf 0 .04 Zt,1� DEV, 6 pA S 15 0 .029 470 375 cf 0 .04 ___ (p fL . DFV ,_61�SS 16 0 .039 470 512 cf 0 .04 l(7'�R LTV 61R& MAN-MADE CHANNELS VARIABLES LIST : Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNE-'S. VARIABLE TO BE SOLVED (Y, Q, B,M, S OR N) ? B Y (FT) ? . 333 RESULTS Q (CFS) ? 0 . 25 M (FT/FT) ? 3 B= 2 . 20 FT S (FT/FT) ? . 02 A= 1 . 06 SF N (FT^1/6) ? 0 . 35 P= 4 . 30 FT V= 0 .23 FPS F= 0 . 08 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to men ------------------------------------------------------------------------------ 66 — �I /4vY *0 t, 5�4 le, (� /C_t{ 4 7�1-1 s MAN-MADE CHANNELS VARIABLES LIST: Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNESS VARIABLE TO BE SOLVED (Y, Q, B,M, S OR N) ? Y Q (CFS) ? 0 . 25 RESULTS B (FT) ? 2 . 50 M (FT/FT) ? 3 Y= 0 . 31 FT S (FT/FT) ? . 02 A= 1 . 08 SF N (FT-1/6) ? 0 . 35 P= 4 . 48 FT V= 0 . 23 FPS F= 0 . 08 SUB-CRITICAL FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to menu ------------------------------------------------------------------------------- MAN-MADE CHANNELS VARIABLES LIST : Y - FLOW DEPTH B - CHANNEL BOTTOM WIDTH S - CHANNEL SLOPE Q - FLOWRATE M - CHANNEL SIDE SLOPE N - CHANNEL ROUGHNES-c VARIABLE TO BE SOLVED (Y, Q, B,M, S OR N) ? Y Q (CFS) ? 0 . 874 RESULTS B (FT) ? 2 . 50 M (FT/FT) ? 3 Y= 0 . 27 FT S (FT/FT) ? . 003 A= 0 . 90 SF N (FT^1/6) ? . 030 P= 4 . 22 FT V= 0 . 97 FPS F= 0 . 37 SUB-CRITICAL- FLOW <Shift> <Prt Sc> print <Return> repeat <Space Bar> back to men, ------------------------------------------------------------------------------- 10/27/98 11 : 44 : 2 am Pacific Engineering Design Inc Page BRIERS PLAT - JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: DBY02 NAME : 2-YR . DEV . BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 . 10 inches AREA . . : 0 .00 Acres 0 .04 Ac TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 5 .00 min S .00 mi ABSTRACTION COEFF : 0 .20 PEAK RATE : 0 .02 cfs VOL : 0 .01 Ac-ft TIME : 470 min BASIN ID : DBY10 NAME : 10-YR . DEV . BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 .95 inches AREA . . : 0 .00 Acres 0 .04 A, TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . 5 .00 min 5 .00 mi ABSTRACTION COEFF: 0 .20 PEAK RATE : 0 .03 cfs VOL : 0 .01 Ac-ft TIME : 470 min BASIN ID : DBY100 NAME : 100-YR . DEV . BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 3 .95 inches AREA . . : 0 .00 Acres 0 .04 A. TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 5 .00 min 5 .00 mi , ABSTRACTION COEFF : 0 .20 PEAK RATE : 0 .04 cfs VOL : 0 .01 Ac-ft TIME : 470 min BASIN ID : EBY02 NAME : 2-YR . EXISTING BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 . 10 inches AREA . . : 0 .04 Acres 0 .00 A TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 5 .00 min 5 .00 mi ABSTRACTION COEFF : 0 .20 PEAK RATE : 0 .01 cfs VOL : 0 .00 Ac-ft TIME : 480 min 10/27/98 11 : 44 :2 am Pacific Engineering Design Inc Page BRIERE PLAT - JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: EBY10 NAME : 10-YR . EXISTING BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 .95 inches AREA . . : 0 .04 Acres 0 .00 AC TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 5 .00 min 5 .00 mir. ABSTRACTION COEFF : 0 .20 PEAK RATE : 0 .02 cfs VOL : 0 .00 Ac-ft TIME : 470 min BASIN ID : EBY100 NAME : 100-YR . EXISTING BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 0 .04 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 3 .95 inches AREA . . : 0 .04 Acres 0 .00 Ar TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . - S .00 min 5 .00 mir ABSTRACTION COEFF : 0 .20 PEAK RATE : 0 .03 cfs VOL : 0 .01 Ac-ft TIME : 470 min 10/27/98 11 :43 : 14 am Pacific Engineering Design Inc PEIg BRIERE PLAT JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: DEV02 NAME : 2-YR . DEV LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 . 10 inches AREA . . : 1 . 16 Acres 1 .08 AC TIME INTERVAL . . . . : 10 .00 min CN . . . . . 86 .00 98 .00 TC . . . . : 5 .00 min 5 .00 mil- ABSTRACTION COEFF: 0 .20 PEAK RATE : 0 .83 cfs VOL : 0 .26 Ac-ft TIME : 470 min RASTN TD : DEV10 NAME : 10--YR . DEV LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 .95 inches AREA . . : 1 .16 Acres 1 .06 A:. TIME INTERVAL . . . . : 10 .00 min CN . . . . .. 86 .00 98 .00 TC . . . . . 5 .00 min 5 .00 mil- ABSTRACTION COEFF : 0 .20 PEAK RATE : 1 .32 cfs VOL : 0 .40 Ac-ft TIME : 470 min BASIN ID: DEV100 NAME : 100-YR . DEV LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 3 .95 inches AREA . . : 1 . 16 Acres 1 .08 A( TIME INTERVAL . . . . : 10 .00 min CN . . . . : 86 .00 98 .00 TC . . . . • 5 .00 min 5 .00 mil ABSTRACTION COEFF: 0 .20 PEAK RATE : 1 .92 cfs VOL : 0 .58 Ac-ft TIME : 470 min BASIN ID : EX02 NAME : 2-YR . EXISTING LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 . 10 inches AREA . . : 2 .24 Acres 0 .00 Ac TIME INTERVAL_ . . . . : 10 .00 min CN . . . . 85 .00 98 .00 TC . . . . : 36 .46 min 36 .46 mi , ABSTRACTION COEFF : 0 .20 TcReach - Sheet L : 300 .00 ns: 0 .1500 p2yr : 2 . 10 s : 0 .0122 TcReach - Shallow L : 70 .00 ks: 11 .00 s : 0 .0122 PEAK RATE : 0 .26 cfs VOL : 0 .16 Ac-ft TIME : 490 min 10/27/98 11 : 43 : 14 am Pacific Engineering Design Inc PEIQF BRIERE PLAT - JOB NO .98016 DRAINAGE CALCULATIONS BASIN SUMMARY BASIN ID: EX10 NAME : 10-YR . EXISTING LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION . . . . : 2 .95 inches AREA . . : 2 .24 Acres 0 .00 Ac TIME INTERVAL . . . . : 10 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 36 .46 min 36 .46 mir ABSTRACTION COEFF : 0 .20 TcReach - Sheet L : 300 .00 ns : 0 .1500 p2yr : 2 . 10 s :0 .0122 TcReach - Shallow L : 70 .00 ks : 11 .00 s: 0 .0122 PEAK RATE : 0 .53 cfs VOL : 0 .29 Ac-ft TIME : 480 min BASIN ID : EX100 NAME : 100-YR . EXISTING LESS BYPASS SBUH METHODOLOGY TOTAL AREA . . . . . . . : 2 .24 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMF' PRECIPITATION . . . . : 3 .95 inches AREA . . : 2 .24 Acres 0 .00 A,- TIME INTERVAL . . . . : 9.0 .00 min CN . . . . : 85 .00 98 .00 TC . . . . : 36 .46 min 36 .46 mir ABSTRACTION COEFF: 0 .20 TcReach - Sheet L : 300 .00 ns :0 . 1500 p2yr : 2 .10 s:0 .0122 TcReach - Shallow L : 70 .00 ks : 11 .00 s: 0 .0122 PEAK RATE : 0 .89 cfs VOL : 0 .45 Ac-ft TIME : 480 min KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1.2.2 CORE REQUIREMENT #2: OFF-SITE ANALYSIS A proposed project initial submittal shall include an Off-Site Analysis Report that evaluates drainage system problems (ponding water, high/low flows, siltation, erosion, etc.) upstream, on-site, and downstream of the proposed project. The design engineer shall demonstrate that the proposed project has been designed so that it neither aggravates (increases the magnitude, frequency, or duration of ) an existing drainage problem nor creates a new drainage problem. Exemption: Permits and approvals requiring drainage review will be exempt from performing an Off- Site Analysis when the BALD Division determines that the proposed development contains sufficient measures to adequately protect the downstream drainage system AND, 1) the proposed new impervious surface' to be constructed is 5,000 square feet, or less, OR 2) the drainage area from which surface and storm water runoff is to be collected and concentrated is 5,000 square feet, or less. Levels of Off-site Analysis The Off-Site Analysis report requirements vary depending on the specific site and downstream conditions. Each project submittal shall include at least a Level 1 analysis. Upon review of the Level 1 analysis, BALD may require a Level 2 or Level 3 analysis. If conditions warrant, additional, more detailed analysis may be required. Level 1 Analysis: The Level 1 analysis is a qualitative survey of each downstream system leaving a site. This analysis is required for all proposed projects and shall be submitted with the initial permit application. Depending on the findings of the Level 1 analysis, the Level 2 or 3 analysis may need to be completed and/or additional information may be required. If further analysis is required, the applicant may schedule a meeting with BALD Division staff. Level 2 or 3 Analysis: If problems are identified in the Level 1 analysis, either a Level 2 (rough quantitative) analysis or a Level 3 (more precise quantitative) analysis shall be performed to further define and evaluate proposed mitigation for the problem. The BALD Division will determine whether a Level 2 or 3 analysis is required based on the evidence of existing or potential problems identified in the Level 1 analysis and on the proposed on-site drainage facilities design. The Level 3 analysis is required when results need to be as accurate as possible: for example, if the site is flat; or if the system is affected by downstream controls; or if minor changes in the drainage system could flood roads, buildings, or septic systems; or if the proposed project will contribute more than 15 percent of the total peak flow to the drainage problem location. The Level 2 or 3 analysis may not be required, if the BALD Division determines that adequate mitigation can be developed from the Level 1 analysis. Additional Analysis: Additional, more detailed, hydrologic analysis may be required if the BALD Division determines that the analysis has not been sufficient to analyze the impacts of a proposed project on an existing or potential drainage problem. This more detailed analysis will generally include synthesizing, summing, and phasing hydrographs for the major drainage areas (defined by major drainage system components affecting routing such as impoundments, restrictions, confluences, etc.) tributary to the drainage problem areas. The SWM Division will review this additional analysis. Specific Requirements for Off-site Analysis: Regardless of the level of Off-Site Analysis required, the applicant shall: define and map the study area (Task 1), review resources (Task 2), inspect the study area (Task 3), describe the drainage system and problems (Task 4), and propose mitigation measures (Task 5) as described below. ' See Definition Section 1.2.2-1 11/92 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN NtANUAL Collect qualitative data on features such as land use, impervious surfaces, topography, and soil types. Collect information on pipe sizes, channel characteristics, drainage structures, wetland/stream/steep slope (Sensitive) areas. Verify tributary basins delineated in Task 1. Contact neighboring property owners or residents in the area about past or existing drainage problems and describe in the report (Optional). Note the date and weather conditions at the time of inspection. Level 2 or 3 Inspection: Perform a Level 1 Inspection. Document existing site conditions (approved drainage systems or pre-1979 aerial photographs) as defined in Core Requirement # 3. Collect quantitative field data (For Level 2, Collect non-survey field data using hand tapes, hand reel, and rods, and for Level 3 collect field survey profile and cross-section topographic data prepared by an experienced surveyor.) Task 4: Drainage System Description and Problem Screening Each drainage system component and problem shall be addressed in the Off-Site Analysis Report: on a map (Task 1), in the narrative, and in the Drainage System Table (See Reference 1013). Drainage system components: The following information about drainage system components such as pipes, culverts, bridges, outfalls, ponds, tanks, and vaults shall be included in the report: Location (corresponding map label and distance downstream/upstream from site discharge) Physical description (type, size, length, slope, vegetation, and cover) Problems Field observations Existing/potential problems: All existing/potential problems (ponding water, high/low flows, siltation, erosion, etc.) identified in the resource review or field inspection shall be described in the report as follows regardless of whether the proposed project may or may not aggravate the problem. Then, problems that are not of concern will be screened from further analysis. Type of problem: magnitude, frequency, and/or duration Description of problem: ponding water, high or low flows, siltation, erosion, slides Magnitude of or damage caused by problem: siltation of ponds, dried up ornamental ponds, road inundation, flooded property, flooded building, flooded septic system, significant destruction of aquatic habitat or organisms. General frequency and duration of problem (Dates and time problem occurred, if available) Design storm or flow (cfs) of the water when problem occurs (Optional for Level 1 and required for Levels 2 and 3) Water surface elevation when problem occurs (for example, elevation of building foundation, crest of roadway, elevation of septic drain fields, or wetland/stream high water mark) Names and concerns of involved parties (Optional for all levels of analysis) Current mitigation of problem Possible cause of problem Why the proposed project will or will not aggravate (increase the magnitude, frequency, or duration) the existing problem nor create a new drainage problem. For example, the problem will not be aggravated if: (1) it is an upgradient drainage problem that will not effect or be affected by project drainage systems; or (2) it is a flooding problem and the project will not increase the elevation, duration, or frequency of elevated water; or (3) it is a capacity problem and the project proposes controls (pipes, culverts, channels, etc.) that will convey runoff as specified in Core Requirement #4: Conveyance System. 1.2.2-3 11/92