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c (7y Project: Houser Way c*VVI AV, Ys i D.Carey N� J 9/15/95 PIPE FLOW CAPACITY BY MANNING EQUAI Version 1 U �' Q= ( 1.49/n)xAxRA2/3xS^1/2 For pipes flowing full, not under pressure conditions Reach Pipe Area Hyd. Rad. Slope n Q( cfs ) Dia.(in) (sq.ft. ) (full, ft) 36 7.069 0.750 0.0025 0.012 36.22 36 7.069 0.750 0.0026 0.012 36.94 36 7.069 0.750 0.0027 0.012 37.64 36 7.069 0.750 0.0028 0.012 38.33 36 7.069 0.750 0.0029 0.012 39.01 36 7.069 0.750 0.0030 0.012 39.68 Page 1 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 40.67 7.83 628124 ENTER [d:] [path]filename[.ext] FOR STORAGE OF COMPUTED HYDROGRAPH: d:\rstraka\Junk FILE ALREADY EXIST; OVERWRITE (Y or N) ? Y SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP c ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 5 38,89, 19,98,20 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN 57.0 38.0 89.0 19.0 98.0 20.0 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 37.48 7.83 627060 ENTER [d:] [path]filename[.ext] FOR STORAGE OF COMPUTED HYDROGRAPH: ********* 100-YEAR 24-HOUR STORM **** 3.90" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 0,0,57,98,7 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN 57.0 .0 .0 57.0 98.0 7.0 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 53.93 7.67 758335 ENTER [d:] [path]filename[ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: d:\rstraka\junk FILE ALREADY EXIST; OVERWRITE (Y or N) ? y SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP c ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 2 CITY OF RENTON MEMORANDUM PLANNING/BUILDING/PUBLIC WORKS DATE: November 9, 1994 TO: Ron Straka FROM: Joe Armstrong SUBJECT: Houser Way Relocation Attached for your review and comment is ENTRANCO upstream analysis for the proposed 36" connection at 8th and Houser. This is the area you suggested they increase the pipe size from 24" to 36" and to show that the 36" would have the capacity. Attachment 11/02/94 17:06 FAX 206 454 0220 ENTRANCO ENG. Cdj002/004 MEMORANDUM Date: November 1, 1994 From; Michael Schwar To: Ralph Nelson Re: Storm drain line entering N 8th Street from the north along Houser Way N Project: Houser Way Improvements Project Entranco Project No. 93010-20 This memo summarizes the information we have regarding the existing Houser Way N drainage system immediately north of the intersection of Trouser Way N and N 8th Street. Existing system The existing drainage line along Houser Way N is a series of concrete pipes from approximately 950 feet north of the N 8th Street intersection to the trunk line along N 8th Street. At the north end a 36-inch corrugated metal pipe carrys flows from the east side of I-405 into the first manhole in the system(see attached figure). Exiting this manhole is a 200 foot concrete pipe that at one time entered a'vault beside the roadway. However, the pipe is broken in several locations and contains a large amount of sediment, and does not appear to carry flows. Additionally, water flows through the roadway fill beneath the corrugated metal pipe crossing under I-405. The flows in this area have cut an 8 foot wide channel east of the pipe, and low flows meander through this channel before entering the vault. Flows exiting the vault flow through a 36-inch concrete pipe running just below the ground surface east of the roadway, There are two breaks in the top of this pipe, but it is not clear that these breaks would have a great impact on the conveyance capacity of the pipe. This pipe apparently ties into a 24-inch concrete stormdrain system somewhere before the 24-inch pipe enters a manhole in the roadway 180 feet to the south_ Also, a pair of roadway catch basins ties into the system approximately 60 feet north of the manhole. The flows continue south in a 480 foot run of 24-inch concrete pipe to the manhole at 200+60. Another roadway catch basin ties into the system approximately 240 feet upstream of this manhole. The pipe leaving this manhole runs 56 feet to the southwest into a catch basin, and then 24 feet south to enter the N 8th Street trunkline at the manhole immediately east of Houser Way N. So�ormflows The total area tributary to this system is 57 acres. The corrugated metal pipe drains 3 8 acres of residential development and 7 acres of I-405. The rest of the tributary area (12 acres) consists of commercial areas immediately adjacent to Houser Way N and the roadway itself Stormflows entering this system were modeled for the Garden Avenue Drainage Study (Entranco, 1991) and are listed in table 1. 11/02/94 17:07 FAX 206 454 0220 ENTRANCO ENG. Ia o0a/004 y Table 1. Flows to Houser Way N system Tributary area Total 10 year 25-year Area(ac.) Flow(cfs) Flow(cfs) 1-405 7 4.7 5.5 Residential area 38 7.9 10.4 Conu=rcial area 12 7.3 8.8 Sum total 57 19.9 24.7 Limitations Three factors limit the conveyance capacity of this system • At the upstream end the physical deterioration of the pipe system limit capacity. Physical deterioration of the upstream portion of this system includes the damaged concrete pipe segments, sedimentation and the undefined problems which cause water to flow beneath the hillside corrugated metal pipe. • In the downstream sections, adverse slopes limit capacity The last two sections of pipe have adverse slopes of 5.9 and 12.0 percent. • The entire system is limited by high tailwaters. Extensive modeling has indicated that the downstream system surcharges for large storm events, and that this contributes to the flooding which occurs during those events. The EXTRAN model of this area indicates that this system would flood during relatively common storm events (less than 10-year return interval), due primarily to the high water levels caused by the downstream adverse slopes, but also partially due to high tailwater levels downstream. Proposed improvements • Repair the eadsting 36-inch section A 36-inch pipe at a*minimal (0.2 percent) slope, either corrugated or concrete would have adequate capacity to carry the 25-year flow in this system. A 24-inch concrete pipe would require approximately a 1.1 percent slope to reach this capacity. • Reset the downstream pipes to eliminate the adverse slopes Eliminating the adverse slopes should improve the conveyance capacity of this system, but an upgrade to 36-inch concrete would be required to accommodate the predicted flows. 11/02/94 17:07 FAX 206 454 0220 ENTRANCO ENG. 17j004/004 n J • Eliminate the tailwater limitation A regional solution would be required to ensure that the conveyance capacity of this system would not be limited by high tailwater levels. �DD jul 0 0.25 0.5 NE 20th S1 l MILE �I 2 L E G E N D % \ Dzy b N0. Basin Number ' -- Basin Boundary / , ---- Sheet Flow ❑ r - — Shallow Concentrated Flow 3 GENE COULON-� Pipe Flow UNORiAL NE 121h ST a D �� a ` BEACH PARK Rig r 9 Q. 9oa 40 D W r LCIOJ W O .o aoo , � r12 a II � 1 Z a N 8th ST r Y I � � h Sl NE �� 16 -10 14 13 10 D� r Z a 17 r 1�z;DF I 15 NE 4t C - _ D \ a ,o �3�� CIA D � ■ D D r a [IDF1 D r � - PARK AVENUE DRAINAGE SYSTEM Figure 4 E N T R A N C o DRAINAGE BASINS In c—D -v, . ENTER OPTION: 2 SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH STORM OPTIONS: 1 - S.C.S. TYPE-lA 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S.C.S. TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP(INCHES) 100,24,3.9 ---------------------------------------------------------------------- ******************** S.C.S. TYPE-IA DISTRIBUTION ******************** ********* 100-YEAR 24-HOUR STORM **** 3.90" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 28,77, 10,98,29.60 SPECIFY STORM OPTION: 1 S.C.S. TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP(INCHES) 100,24,3.9 ---------------------------------------------------------------------- ******************** S.C.S. TYPE-lA DISTRIBUTION ******************** ********* 100-YEAR 24-HOUR STORM **** 3.90" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 28,77, 10,98,29.60 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN 38.0 28.0 77.0 10.0 98.0 29.6 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 14.40 7.83 307410 ENTER [d: ] [path]filename[ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: . ENTER OPTION: 2 SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH STORM OPTIONS: 1 - S.C.S. TYPE-lA 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S.C.S. TYPE-IA RAINFALL DISTRIBUTION ENTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP(INCHES) 25,24,3.4 ---------------------------------------------------------------------- ******************** S.C.S. TYPE-IA DISTRIBUTION ******************** ********* 25-YEAR 24-HOUR STORM **** 3.40" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 28,77, 10,98,29.6 SPECIFY STORM OPTION: 1 S.C.S. TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP(INCHES) 25,24,3.4 ---------------------------------------------------------------------- ******************** S.C.S. TYPE-lA DISTRIBUTION ******************** ********* 25-YEAR 24-HOUR STORM **** 3.40" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 28,77, 10,98,29.6 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN 38.0 28.0 77.0 10.0 98.0 29.6 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 11 .45 7.83 251248 ENTER [d:] [path]filename[ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: soy-L,s4 - 0-13 SPECIFY STORM OPTION: . I S.C.S. TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP(INCHES) 100,24,3.9 ---------------------------------------------------------------------- ******************** S.C.S. TYPE-lA DISTRIBUTION ******************** ********* 100-YEAR 24-HOUR STORM **** 3.90" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 14,83,23,98,26.3 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN 37.0 14.0 83.0 23.0 98.0 26.3 PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT) 22. 18 7.83 415390 ENTER [d: ] [path]filename[ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: QED-23-'95 THU 14:32 ID:WSDOT FLR 5 DIST 1 TEL N0:206-440-4005 #623 P01 Facsimile Cover Sheet AA���� To: Ronald J. Stray Company: City of Renton Eng. Phone: 277-5548 Fax: 235-2541 From: Manny Quinteirc Company: J. Johnson Design 0', Region Phone: 440-4569 Fax: 440-4805 Date: 02/23/95 Pages including this 11 cover page: Comments: This is the propose Drainage Plan for Houser Way We are also including The Pipe Sizing Spread Sheet, The Soil Analysis, Pipe Alternative and the Specs Criteria for Soils and Protective Treatment. The prefer Method of Treatment is Aluminized 0.16 gage Steel Culvert Pipe. Please call if you have any question Manny N a- r1) N �D U) m CD zw I I I D ID I LID N I~2r ca+C P O It IQ Z 1/ w / I— C,,,1/ 1, S Icy t d -----' WAY r1K UF) LL 1q pl I'tKl' v �a O CIO I'll IN D F Iv6ly+�vf!`r.a�l W KKI A My w !� TA rEa.Aio rltor.►�0. PNORW aVELOMt i o A D11►fStON wool logo 1� �, PM h' M. 7 sOr�ht OI 1401m P?O'rIon •P UNFA gum. 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ADM. nan fan "vision !K - 1 i �St=cCFGs= I HS 1 WAY GUTTER FL OV SPA06 W04 Order Entered By M.J.Ouimelr0 _ RdIt1's11 Cotlsdttts MP/00.0I to MP 000.00 Otp Unil 412353 (See WSOOINy*aulc Hamm(prpo2-9) PRKPIP] Project Nuns Data: FEB. 20, 1995 YEAgSTORM Project Description 10 25 100 rill5.626.75 It 0.63 0.539 0.545 (f) Laadoa D(txllarpe SewnDtslpn 11- 0(7 lD Runtype "Mif On from To Storm Souce Acres C Acres C AC Sum AC Start Time End 1 O Disc. Oise.a- Capacity Die. n Velocity Invert fl Yw9 enope L 334+32(O'RT) 334+32(70'L 25 0.00 0.9 0.00 0.3 0.00 7,13 13.18 0.08 1126 1.71 12.21 12.21 106.6 36 0.012 15.09 69.32 CV TvvobwerU H2 334+32(70'l 333+75(144, 25 0.00 0.00 7.13 0.03 13.28 1.71 12.19 12.19 373.7 36 0.012 57.81 87.90 W TwobrAwu H3 333+75044. 333+20098' 25 0.11 0.9 0.00 0.10 7.23 0.03 1131 1.71 12.35 12.35 338.8 36 0.012 47.97 43.00 TwoknwU H4 3+ZO(i ja 1 330+89(207' 25 0.04 0.9 0.04 7.27 0.75 14.07 1.66 12.05 12.05 38.8 36 0.012 6.21 31.26 Tworwerts H5 330+69(207' 330+05(211' 25 0.00 7.27 0.27 14A3 1.64 11.92 11.92 37.6 36 0.012 5.32 30.67 In m J7oA.V v' O V I L9 Vauf Pr I iD 19 CV roARLMA7EPA&'ru Pa-C.awar EOg"-II&M-A(A RWE O Z J W f- H U) A (f) ly- Li H O Q U) 3 a LF) r� v (n m �I r� CV I W W LL- Pipe 1 lock LmVth Slope Invert Grata Cover Grate Cover 70 118 67.60 90.90 18.7 91.80 21.0 92.65 o.26n 43.00 91.80 21.0 55.00 9.0 77.75 0.2200 31.28 55.00 9.0 36.00 1.7 235 0.0026 30.67 36.00 1.7 34.58 0.9 65 0.0027 30.44 34.56 0.9 35.11 1.7 NOTE: Cover N2.3 The Aiiinun Cover dietenpe 18.7 Shown epplioa to a M'Oia. Pipe 21.0 Ube calunn Gal la Cover on 9.6 Comogated Meld l Arch 2_3 1.5 • ;ter- , .,� pH an& RESISTIVITY TESTS o - CUEfl`$ACT ir(1. : �- 03 DATB: .....__..._ •- -, uln�,►���"o f'•:�� I•,I 1 ��t� I.tdSPECTOt: A SECTION: _ RESISTIVITY NO. S` A,7ION OFFSET DEPTH � r ` � DESCRIPTION OF MATERIAL WJKTSR SOIL F._ELD LAB. -- Inc - _.. __ .._._ - •-----�__•___ - - ---LAB --- - r-.r"---=_ IJJ7f �t 0 Cif� J� � 1 I rn _ In a J LL _ 1 t el LLI LL r� � � 1 FED-23-'95 THU 14:36 I D:WSDOT FLP. 5 D I ST 1 TEL N0:206-440-4e35 tt623 P07 ABSTRACT 0004 NORTHWEST REGION HYDRAULIC SECTION FOR PIPE ALTERNATES REVISION DATE: 2123195 Table of Content- Page History,Design Cumidcrudotu 2 Structure notes 3,4 General special provision for storm sewers 5 General apeeial provision for corrugated polycthylcnc 6 Revised Minnings"n'for comipited pipe 7 PAGE 1 FEE-23—'95 THU 14!S? I D-WSDOT FLP. 5 D I ST 1 TEL NO!206-443-4235 tt62.5 P22 ABSTRACT 0004 z/a 3/g,- History 'lire attached structure notes were originally prepared in 1988 in response to the Headquarters IDC of 6119/87 and the advent of uitticatcd pipe alternates being allowed for storm sewer application. Prior to about 1985 metal pipe for storm sewers required treatment to control leakage throtigh the seams. The advent of gasketed and welded seams on aluminum and galvanized or aluminized steel pipe addressed the leakage issue,but did itut address the incmasod hydraulic loss due to corrugations. An additional three inches was added to offtet the hydraulic losses. Hydraulic losses were also addressed in an IDC of June 29, 1993 from headquarters,sec attached, Revised A,iammng'c"n"are relayed in that IDC and an FHWA puhlication,HDS#5 is rrferentsd- The rturumum uades Riven in that IDC should be observed when all pipe altcriurtcs arc allvwcd. Concrete or Plastic should be used where even flatter grades are required. The additional three inch allowance for hydraulic ins m in metal pipe is still recommended to compensate for the additional hydraulic losses and to provide capacity when and if the inverts rust. Tlic added three inches will also compensate for the 3+%reduction in the flow area with metric conversion of 25 rather than 25.4 mm/inch Design Considerations Pipe altunates are listed in structure notes. (,enerally,ac many alternates as Dossible should be shown on the plans. Pipe alternate selection is based on . 1. Hydraulic capacity. 2. Resistivity and pH of the site. Resistivity and pH readings are developed by the materials Section- 3. Cover limits are defined in section 8 of the Hydraulic Manual.. 4. Velocity paranictcrh aic dixuascd lit the hydraulic Manual. Ccncrally a minimtun of three feet per second,calculated with full flow,should be provided for storm sewers-,two feet per second for sanitary sewers. Siphons should have at least 5 feet per second and preferably more_ An upper vclucity limits of 10 feet per second is desirable. Pipes with steeper slopes should be used with consideration for abrasion ofbedload,volume ofwater,ease of repair,and cost of replacement. 5. Bed load is a subjective issue and mtay be discussed«zth the hydraulic section. Aluminized steel with extra wall thickness should be used for highly abrasive sites. F Minor pipes.tabulated on Daze 1i-6 of the Hydraulic Manual,are not treated. The attached structure notes are suggested for contract preparation. They reflect current practice ac plastic becomes an aeccptaOle alternate for storm scwcr and Schedule A Culvert pipe. PAGE ? FED-23—'95 THU 14:37 ID:WSDOT FLR 5 DIST 1 TEL NO:206-440-4005 #623 P09 ABSTRACT 0004 TYPICAL STRUCTURE NOTE RECOMMENDATIONS FOR PIPE ALTERNATES CONDITIONS: Zone 2 where resistivity > 1000 ohm-cm, pH > 5, or pH < 8.5 Acceptable alternates for STORM SEWER PIPE are.- Galvanized Steel Storm Sewer Pipe: - Tr. 5. " thick. - Tr. 2,with welded or gasketed longitudinal seams, thick diameter 3 inches larger and profile 3 inches lower than specified. Aluminized Steel Storm Sewer Pipe: - Tr. S. thick. - Plain with gasketed or welded and remetalized longitudinal seams, thick, diameter 3 inches larger and profile 3 inches lower than specified. Aluminum Storm Sewer Pipe: - Tr. 5. " thick. - Plain with gasketed longitudinal seams, " thick, diameter 3 inches larger and profile 3 inches lower than specified. Spiral Rib Storm Sewer Pipe: - Plain aluminum or plain narrow pitch aluminum, thick. - Plain aluminized Steel or plain narrow pitch aluminized steel . thick. - Tr. 2 galvanized Steel or Tr. 2 narrow pitch galva �dsteel . thick. Thermoplastic Storm Sewer Pipe: - Conforming to section 9-05.19. Size not to exceed 24". Cover not to -exceed 15 feet. Acceptable alternates for CULVERT PIPE are: - Treatment 2 Galvanized Steel Culvert pipe. thick. - Plain Aluminum Culvert Pipe thick ` 0/ 4%. Corrugated Polyethylene pipe per AASHTO M 294S, cover not to exceed 15 feet, diameter not to exceed 24 inches. For CULVERT SCHEDULE PIPE (standard plan B-17), the following notes should be added to the structure note sheet: - Galvanized Steel Alternate shall have Treatment 2. - Corrugated Polyethylene pipe per AASHTO M 294S for Schedule A (diameters 12 18", and 24-) only. Acceptable alternates For DRAIN AND UNDERDRAIN PIPE are listed in the standard specifications. No treatment is required and no additional notes are necessary on the structure note sheets. Note: Concrete pipe may be used on slopes up to 10 percent and corrugated metal pipe may be used on slopes up to 20 percent without special consideration. For steeper slopes. consult with the district hydraulics section. PAGE 3 FED-23-'95 THU 14!30 I D:WSDOT FLR 5 D I ST 1 TEL 1`10!2OG-443-4905 tt623 P12 $-5_2 C7prrnenlpn Znne rl Most of Western Washington (exceptions noted helow) along with the three areas of East.rn Washington identified above make up Corrosion Zone 11. This is an area of moderate rorrnsinn Activity. Generally, Treatment 2 is needed to provide rorrosion prntertinn for galvanized steel culverts and storm sewers. Treatment 5 Is needed for storm Ae.werA if the pipe seams are not prestige, tight. WpId►d,gasketed,or pressure tight centinuouc helical lock seam pipe may be used with only Treatment 2_ Untreated aluminized steel and untreated aluminum alloy as well as concrete pipe may be used in Corrosion Zone 11. Parts of western Washington whirh are not located in Corrosion Zone 11 are placed into Corrosion Zone 111. They Include: whatcom County lowlands Lower Nisqually Valley Coastal areas subject to saltwater or salt spray Z-3.3 Corrosion'Lone W The severely corrosive areas Identified above make up Corrosion Zone U1. These areas require asphalt linings similar to Region 11 and, In addition, require the fiber bonded treatment to enhance the asphalt hnnd iind#r these harsh conditions. Generally, Treatment 4 is needed for corrosion protection of culvert pipe. Treatment 6 may be needed for storm sewers if the pipe seams are not pressure tight. Wcldcd, gasketed or lock seam pipe may be used with only Treatment 4 for storm sewer pipe. Untreated aluminized steel and untreated aluminum alloy are not permitted in this region. E4.4 pH of Soil When the pH of the soli 15 less than 3 or greater than 8.3, the site Will be considered unsuitable and only Corrosion Region III pipes would be acceptable(fiber bonded galvanized steel pipe). The designer has the option to average several pH tests within project limits if it is reasonable to do so. This may allow all pipe to have similar treatment within a single contract to simplity contract administration. All projects Involving culverts require at least one pH test. The project engineers judgment should be used to dctcrmine the total number of tests. Where longer jobs are located in historically corrosive areas, tests should be taken in seYeral locations. 8-3.5 Reelattvity of Soil A resistivity test is required on all projects involving culverts. 11 the restatiYlty is less then 11000 ohm CM than Corrosion Region 111 pipes would be the only acceptable alternates. The same criteria for pH shall apply to the frequency of testing for resistivity. c Mav 19R9 FED-23-195 THU 1,1:30 ID:WSDOT FLP. 5 DIST 1 TEL N0:206-1/10-4905 tt623 P11 3c3.21) Aluminum Alloy Aluminum alloy pipe is permitted anywhere that aluminized steel Is permitted and In addition It will be allowed In areas with unfavorable soil reslsilvitles readings(less than i,000 ohm CM). Aluminum alloy pipe is nut recunnnendcd when backfill uratcrial has a very high clay l;untent. 8-3.2E Protective Treatment All types of metal Pipe may require at certain uses and lucatiuns a protective asphalt orating. The coatings, if required, will be placed on circular as well as pipe arch culverts. Structural plate pipes do not require protective treatment other than the 30 percent increase in galvanizing. Drain pipe, underdraln pipe, fruitage ruads, driveway uulverts, dial road appruat h uulyerts du not require any asphalt protective treatment regardless of their corrosion zone, pN readings,or resistivity readings. Wirer prutm;tive cuatirrg is required, lire tteatiueut apmiried in tl.i> bm;tiun ip Lire btandarJ urirdmum application which is adequate for the large majority of installations. When it is determined that local conditions arc such that the protective coatings provided in this guide are not sufficient, the engineer should specify an adequate protective coating. When unusual abrasive or corrosive conditions arc anticipated and it is difficult to determine which treatment would be adequate, It is recommended that the Headquarters Materials Laboratory or the Hydraulics Section be consulted. Protective asphalt treatment is primarily intended to resist corrosion in aggressive soils and other harsh cn.irunnrcu A. The i.urrasWir zone ciiteria is listed bcluw in S"Llvn 8-5. Tire engineer slrail Jc lcr mine ilia required protective treatment In conformance with this section and any other requirements contained elsewhere in this chapter. The applicable treatment, if any, must be specified on the structure note sheet. In addition to resisting corrosion, protective asphalt treatment is sometimes needed to seal the helical seam on the pipe so that it is able to pass a pressure test. Crimped helical seem pipe used for storm sewers will require treatment 5 for this reason regardless of location. Treatment S covers 100 percent of the circumference with asphalt pavement. Some of the treatments(T-2 and TJi)require asphalt paved Inverts for at least 40 percent of the pipe circumference. It hat been found that the inside coating of the culvert above the normal water mark is not unially attacked. Below the normal water mark, the protective coating suffers from wet and dry cycles and erosion-abraslon effects A saver* bed load stream may serve to remove the protective coating in relatively fe- years. For these reaaona, the bottom 40 percent of the pipe Is most critical and, therefore,paved with asphalt. Some protective treatments (T-3, T-4, T.6) require the use of fibers embedded in the tpelter coating_ These fibers imprnvs- thp hrnding hntwo►n the- asphalt crating anA the galvanized coating. Fiber embedded treatments arP required in Corrosion Zone Ill(Nisqually, Whatcom Lowlands,and saltwater spray areas). Fiber bonded is only available for galvanized steel. It is not available for aluminized steel or aluminum alloy pipe. It is also not available for any of the helically manufactured pipe. Fiber bonded corrugated steel pipe is only available ,VAy 1929 8 -6 FED-23—'95 THU 14!39 iD:WGDOT FLP. 5 DIST 1 TEL N0:236-410-4235 tt623 P12 - � r with annular corrugations and riveted seams. Therefore, the fill height tahlev in this manual do not apply. All proposed pipe with thl: treatment shall bt submitted to the Hearlgri.arterra Hydraulic Section for structural design prior to plan preparation. The following table is a summary of thoa six different protective treatments used for metal pipe. Treatment 1 r..nated uniformly inside and out with asphalt. Treatment 2 r'nateri uniformly inside and out with asphalt and with an asphalt paved invert. Treatment 3 CnatPd inside and out with fibers embedded in the spelter coating and then covered nn both sides with asphalt. Treatment 4 Coated as in Treatment 3 and with an asphalt paved Invert. 7r,-nrment S Coated inside and out with asphalt and a 100 percent periphery inside spun asphalt lining. Treatment 6 Coated as in Treatment 3 and with a 100 percent periphery inside spun asphalt lining. 9-3.3 plastic P Plastir pipe is permitted anywhere in the State regardless of corrosion history (subject to the size and structural limitations below). 9.3.3A Corrugated Polyethylene Corrugated polyethylene(PE) pipe is permitted for drain and underdrain pipe up to 24 Inches In diameter. Pipe up to 8 inches in diameter shall meet the requirements of AASHTO M-232. Over 3 Inches to diameter use AASHTO M-294. Corrugated polyethylene pipe is an acceptable alternate fur culves is up to 24 inches in diameter except it is not permlTted under interstate highways. The minimum fill height alluwcd is 2 feeg the maximum fill height v.er PF culverts is 13 feet. The ends of a corrugated polyethylene culvert must be beveled with a concrete headwall or have an aluminum alloy flared end section attached. Either ern) section shall be incidental to the cost of the pipe. Corrugated PE pipe is not suitable ror storm sewer use since the cuupliugs arc unable to pass a pressure test. 8-3.39 Polyvinyl Chloride Polyvinyl chloride pipe(PVC) is perrssitted for drain and underdrain pipe up to 3 inches in diameter. PVC is nut allowed for any use as a culvert pipe or a storm sewer pipe. PVC is commonly used for sanitary sewers because of its smooth wall and good corrosion resistant properties. However, it is not permitted rllr•rtly imrinr a state highway without a casing which meets the structural and corrosion properties of a culvert. $_3.4 Eiturnirtiacd Fiber Situminized fiber pipe is permitted for underdrain pipe only. Q 7 May 1939 zlog%ss' MEMORANDUM To: Ron Straka City of Renton Suface Water Utility From: Michael Schwar, P.E. Entranco Date: February 14, 1995 Re: Response to comments on Houser Way Improvements Project Entranco Project No. 93010-20 In response to the questions and concerns you expressed in our February 1 conversation, I have gathered information regarding Entranco's hydraulic analyses of the North Renton Drainage Basin, especially that dealing with the proposed Houser Way Improvements. This memorandum summarizes that information, and I hope answers those questions. For the sake of brevity, I have referred to past studies wherever possible. The hydrologic analysis conducted for the Garden Avenue Drainage Study (Entranco 1991) provides the flows for the hydraulic analyses. The basins in the vicinity of Houser Way North, including those on 1-405 were further refined for the Houser Way North Regional Drainage Analysis (Entranco 1993a). Although the land use assumptions were for existing land uses, the only undeveloped area tributary to the Houser Way Improvements Project is that on which the project is being built (Entranco 1991, Figure 5). The flow volumes predicted using SCS modeling were compared to measured flows for portions of the North Renton Basin (Entranco 1993b) and found to be consistent, indicating that the representation of the existing basin is reasonable. Hydraulic analyses were initially conducted using a step backwater approach (Entranco 1991 and addenda). It was subsequently decided to use a dynamic flow routing approach to allow us to provide an analysis and design that takes into account storm runoff volumes. The hydraulic analyses indicate that the pipe system along North 8th Street limits the flows in the system upstream of Garden Avenue North, and that significant flooding occurs at storms less than the 10-year event in the vicinity of North 8th Street and Houser Way North. For example, as the Houser Way Relocation-Stormwater Summary sheet (attached) indicates, approximately 92 cfs of flow is delivered to the North 8th Street pipe system for the 2-year event, but the maximum flows through that system are only about 78 cfs. We found that placing a second pipe along North 8th Street could eliminate the restriction in the downstream conveyance capacity and greatly reduce the flooding in the vicinity of North 8th Street and Houser Way North. However, any pipe larger than a 36-inch diameter concrete system would cause tailwaters to rise at the PACCAR outfall and begin to limit discharge. As a result, a 36-inch pipe upgrade was recommended in the Houser Way Improvements Project Technical Information Report (Entranco 1994a). There was some indication that the tailwater effects may be mitigated by removing cross-connections between the two pipe systems running beneath Garden Avenue North, but further modeling would be required to determine if this would allow a larger pipe to be installed along North 8th Street. For design of the Houser Way Improvements Drainage System, we assumed that the upgrade to the North 8th Street drainage system was to occur at some time in the future. For that reason, all regional conveyance through the project was to be confirmed for the 25-year event with improved downstream conditions. Additionally the system was designed so that flooding in the proposed conditions would be less than the existing flooding. The existing flooding also required several Administrative Code Modifications as outlined in the March 15, 1994 memorandum (Entranco 1994b). I have compiled a list of flows, water levels and flooding quantities as generated by EXTRAN and have appended them to this memorandum. Finally, we have looked at the line that currently ties into the drainage system through the area which will be excavated to create the wetland. This pipe is currently at a severe adverse slope and will be tied into the next downstream manhole at a positive slope. This will ensure that the drainage upstream of this pipe will be improved. The EXTRAN modeling had indicated that this catch basin acted as a pressure release, causing flood waters to enter the North 8th Street/Houser Way North intersection. In the proposed conditions, this pressure release would occur into the detention pond and the wetland, resulting in somewhat less street flooding than in the existing conditions. Again, I hope this memorandum helps to resolve the questions that you still had regarding this analysis. If you have any more questions, please call me or Ralph Nelson at 454-5600. REFERENCES Entranco 1994a Houser Way Improvements Project Technical Information Report. Prepared for the City of Renton. January, 1994. 1994b Memorandum from Ralph Nelson, Entranco to Ron Straka, City of Renton Surface Water Utility. March 15, 1994. 1993a Houser Way North Regional Drainage Analysis. Prepared for the City of Renton. January 1993. 1993b Technical Memorandum to Joe Armstrong, City of Renton. June 4, 1993. 1991 Garden Avenue Drainage Study. Prepared for PACCAR, Inc. October 1 , 1991 . Houser Way Relocation- Stormwater Summary Existing Regional Drainage in Vicinity of Site (cfs) Runoff to N. 8th St. Runoff to southern end of Return from hill-side Houser corridor Interval (Sub-basins 6, 7 and 17) (sub-basins 8, 16 and 1405) Total 2-year 65 27 92 10-year 107 45 152 25-year 131 55 186 100-year 155 65 220 Runoff From Houser Way Project Site (cfs): Return As % Interval Existing w/Roadway_ Increase of total 2-year 0.5 1.1 0.6 0.7% 10-year 1.2 2.1 0.9 0.6% 25-year 2.2 3.3 1.1 0.6% "target" Comparison of Stormwater Volumes (acre-feet) Design Volume Existing flood storage provided on-site (below EL 36)= 0.44 Increased runoff by project: 2-yr 0.23 Q 67 ; 10--yr 0.30 Q 74 0 100-yr 0.36 80 Detention volume required (according to standards)= 0.23 0 67i On-site storage being provided (below EL 36): Dead Live Storage Storage Total Swale 0.00 0.45 0.45 Wetpond 0.33 0.20 0.53 Wetland 0.00 0.60 0.60 Totals: 0.33 1.25 1.58 Note: "Target Design Volume" represents the flood storage volume currently provided on-site, combined with various totals representing increased runoff volumes from the project site. The active flood storage volume provided by the project is 1.25 acre-feet, which is greater than any of the "Target Design Volumes" calculated. EXTRAN Modeling Results for Houser Way Improvements Project 2-year storm WSEL(ft.) Flow (cfs) Existing Proposed Existing Proposed North 8th and Houser Way North 34.2 35.1 77.0 78.6 Houser Way detention pond 34.7 35.9 27.9 27.1 Ditch Sta 33+00 -- 36.0 24.8 Ditch Ste 26+50 -- 38.7 27.8 29.7 Ditch Ste 19+50 - 41.5 29.8 10-year storm WSEL(ft.) Flow (cfs) Existing Proposed Existing Proposed North 8th and Houser Way North 34.8 35.2 78.4 79.6 Houser Way detention pond 36.0 36.0 43.1 23.3 Ditch Ste 33+00 36.0 22.8 Ditch Ste 26+50 39.2 61.6 61.3 Ditch Ste 19+50 41.9 61.3 25-year storm WSEL(ft.) Flow (cfs) Improved Conditions Existing Proposed Existing Proposed WSEL (ft.) Flow (cfs) North 8th and Houser Way North 34.8 35.3 78.6 80.1 32.3 160.1 Houser Way detention pond 36.0 36.0 43.2 23.4 35.5 70.0 Ditch Ste 33+00 36.0 23.4 35.6 70.2 Ditch Ste 26+50 39.3 68.1 67.5 39.3 67.2 Ditch Sta 19+50 42.0 67.1 42.0 67.7 100-year storm WSEL(ft.) Flow (cfs) Existing Proposed Existing Proposed North 8th and Houser Way North 34.8 35.3 78.6 80.2 Houser Way detention pond 36.0 36.0 42.8 23.4 Ditch Ste 33+00 - 36.0 23.1 Ditch Ste 26+50 39.4 71.6 72.0 Ditch Ste 19+50 42.1 73.2 Total Flooding (acre-feet) Existing Proposed Improved 2-year 1.0 0.7 10-year 10.4 9.4 25-year 18.4 17.0 0.1 100-year 25.8 24.7 1 Ho use& (,t/ff Al / C Co�7crc-fc � 992 ««« ,n »»>N �©� n 1 e�RTti a0000 Qti��ww N ' g�N��� �gggs< w N 120 ��� H = /•33 f t 4 t Wd = 120 L X 1. 33 f4 x 3. 6 = 586 i�/LF 0.0 = yy „ IF = 3 tiy D = 36 " GE = 35. 11 2 . LIVE Lo A O C ov6r 3D , 4y l f V Pry 92 �rrJJur� c,JL 3 , 33 wL P = TV--t l Sur,-k« Ltl ,(fl /olj — - l 1. 33 � �{ y.lD �'= 32 ALL= (0, lg 3 1• �S f�f� < .7. 6 T �. S t/ / Prrsn art.. wL = 3 Z, 000 16 ( I, 2� V 39,you ( 0.83 + /. 7S< 3.17x8.olf2 2 7,,+- l LI-tJL t o d ova Wj = InJL L J L L - /CM17� a �L L 3, 17 I 1 SL = Ok lsc sP� F �a;�� or ALL wwwwww 3 . 6 �+ o r 3. aaaaaa 000000 ¢_ __ 3.17 Ff x 3. 7pnw ww33 woo "T�1('1 Z NwrC0 �8 8 WL = L—IVL LU4� d �,�JC- mNN / cfr Le 3D<13f,1 (v ✓YJ �L = WT y / , SSS h 21 E 7. �s {-tLF No TZ-- Tu �lG L/S q,'vc J 2 19/0 f .S /20 ) = 2 862 k 3. B E-DDING FACTOR Frc-11, l-;j 4 r c. 2 2 -7 c 1 4J1 C C B = f, 5 L��� �ir C� �� �kw SO, /s .�. Fe, c j—< o - Sk f/ Fee-- 14sT/4'1 0.01 �h� c�-� k A c0-7C. Ao,/7C- y3) D,oi = w� -f 1We x FS 13f x D 2882 + 586 x fO /, s" x 3 /DOD 16 �tr -6+ '4 IZ1SjdG ��C�i✓/C�l 6c I ( I J x' d .fir-.-.......,,....... ._......... ._.. ._..... ... ....�.... _.:a.....a.,.w. i6��.r A HIGHWAY LOADS , ..>.. ...., ON CIRCULAR PIPE POUNDS PER LINEAR FOOT r m Bc HEIGHT OF FILL H ABOVE TOP OF PIPE IN FEET 4b cn (ft.) 0.5 1.0 1 1.5 2.0 1 2.5 3.0 1 3.5 4.0 1 5.0 6.0 1 7.0 8.0 9.0 12 1.33 3780 2080 1470 1080 760 550 450 380 290 230 190 160 130 12 15 1.63 4240 2360 1740 1280 900 660 540 450 350 280 230 190 160 15 18 1.92 4110 2610 1970 1460 1030 750 620 520 400 320 260 220 190 18 21 2.21 3920 2820 2190 1620 1150 840 690 580 450 360 300 250 210 21 24 2.50 4100 3010 2400 1780 1270 930 760 640 500 400 330 280 240 24 27 2.79 3880 2940 2590 1930 1380 1010 830 700 560 440 360 300 260 27 30 3.08 3620 2830 2770 2070 1480 1080 890 750 590 480 390 330 280 30 33 3.38 3390 2930 2950 2200 1580 1160 960 810 630 510 420 360 300 33 w 36 3.67 3190 2810 2930 2330 1670 1230 1020 860 670 550 450 380 330 36 = 39 3.96 3010 2670 2850 2440 1760 1290 1070 910 710 580 480 410 350 39 U 42 4.25 2860 2550 2770 2560 1840 1360 1130 950 750 610 510 430 370 42 m Z 48 4.83 2590 2330 2620 2480 1990 1470 1230 1040 820 670 560 470 410 48 Ln Z 54 5.42 2360 2150 2490 2360 2050 1580 1320 1120 890 730 610 520 440 54 0 60 6.00 2170 1990 2450 2250 1960 1680 1400 1190 950 780 650 560 480 60 m ,q 66 6.58 2010 1850 2520 2160 1880 1640 1480 1260 1010 830 700 590 510 66 - w 72 7.17 1870 1730 2580 2190 1810 1570 1510 1330 1060 880 740 630 540 72 Z lZ N r., N 78 7.75 1750 1630 2630 2240 1770 1520 1460 1390 1110 920 780 660 570 78 z � w 84 8.33 1650 1540 2730 2290 1810 1460 1410 1360 1160 960 810 690 600 84 n 90 8.92 1550 1460 2530 2330 1850 1470 1360 1310 1210 1000 850 720 630 90 m °' 96 9.50 1470 1380 2410 2290 1880 1500 1330 1270 1250 1040 880 750 650 96 N 102 10.08 1390 1320 2300 2190 1910 1530 1350 1240 1290 1070 910 780 680 102 108 10.67 1320 1260 2200 2090 1830 1560 1380 1230 1330 1110 940 810 700 108 114 11.25 1260 1200 2110 2010 1760 1540 1410 1260 1362 1140 970 830 730 114 120 11.83 1210 1150 2020 1930 1700 1480 1420 1280 1400 1170 990 860 750 120 126 12.42 1160 1100 1940 1860 1640 1430 1380 1300 1430 1200 1020 880 770 126 132 13.00 1110 1060 1870 1800 1580 1380 1330 1290 1460 1220 1040 900 790 132 138 13.58 1070 1020 1800 1730 1530 1340 1290 1250 1490 1250 1070 920 810 138 144 14.17 1020 980 1740 1670 1480 1300 1250 1210 1470 1280 1090 940 830 144 DATA: 1. Unsurfaced roadway. 2. Loads-AASHTO HS 20, two 16,000 lb. dual-tired wheels, 4 ft. on centers, or alternate loading, four 12,000 lb. dual-tired wheels, 4 ft. on centers with impact included. NOTES: 1. Interpolate for intermediate pipe sizes and/or fill heights. 2. Critical loads: a. For H =0.5 and 1.0 ft., a single 16,000 lb. dual-tired wheel. b. For H = 1.5 through 4.0 ft., two 16,000 lb. dual-tired wheels, 4 ft. on centers. �- c. For H > 4.0 ft. alternate loading. 0` 3. Truck live loads for H=10.0 ft. or more are insignificant. W --- - -- JN 08:58 P. 03 3/ 4D C 76 TABLE 2 Design Requirements for Class If Reinforced Concrete Pipe" NOTE-SCa SOCtlon 5 for basis of aoceplance specified by the pUrChaSor. The strength test requirements In pounds force per linear foot of pipe under the three-edge-bearing method shall be either the D-toad (lest 1`030 expressed in puunds-force per linear foot per foot of diameter)to produce a 0,01-In, crack,or the D-loads to produce the 0.014n.crack and the ultimate load as specitlod below, multiplied by the internal diameter of the pipe In feet. Now to produce a 0.01-in.crack 1000 D-load to produce the ultimate load` 1500 Reinforcement,In.2pinear it of pipe wall We"A w44 B Wall C Internal Concrete Strength,4000 psi Concrete Strength.4000 psi Designated g p Concrete Strength,4000 psi Diameter. Circular Circular Circular in. Wail Reinforcement° wall Reinforcament° Wall c Elliptical Elliptical Rein}prcerrlent Elliptical Thickness. Reinforcement` Thickness. H intoreementc Thicknoss, o in Iruler Outer ku Inner Outer a In Inner outer Reinforcement Cage Cage Cage Cage Cage Cage 12 1V. 0.07, ... 2 0.079 ... ... 234 0.070 ... 15 11A 0.078 2V. 0.070 3 0.079P 18 2 0.07° 0.0711 21h 0,078 ... 0.078 31A 0.078 0,079 21 21/. 0.12 ... 0.10 23/. 0,070 ... 0.079 31S 0.0711 0.079 24 2V2 0.13 0.11 3 0.07° 0.07° 334 0.070 ... 0.0711 27 21/a 0.15 0.13 31/. 0.13 ... 0.11 4 0.07° 0,07a 30 22/. 0.15 0.14 31A 0.14 ... 0.12 4'A 0.07° 0.0711 33 71/9 0.16 0.15 32/. 0.15 0.13 4'h 0.07' 0.070 36 3 0,14 0.08 0.15 4 E D.12 0.07 0.13 4;4 f 0.07 0.07 0.08 42 31/: 0.16 0.10 0.18 41/2 0.15 0.09 0,17 5'A 0.10 D.07 0,11 48 4 0.21 0.13 0.23 5 0.18 0.11 0.20 534 0.14 0.08 0.15 54 41/2 0.25 0.15 0.28 5'/2 0.22 0.13 0.24 6'A 0.17 0.10 0.19 GO 5 0.30 0.18 0.33 6 0.25 0.15 0.28 634 0.22 0.13 0.24 66 5'/2 0.35 0.21 0.39 61/2 0.31 0.19 0.34 7'A 0.25 0.15 0.28 72 6 0.41 0.25 0,45 7 0.35 0.21 0.39 734 0.30 0.18 0.33 78 6'/2 0.46 0.28 0.51 71/2 0 40 0.24 0.44 81A 0.35 0.21 0.39 84 7 0.51 0.31 0.57 a 0.46 0.28 0.51 834 0.41 0.25 0.46 90 71/2 0,57 0,34 0.63 81/2 0.51 0.31 0.57 914 0.48 0.29 0,53 96 8 0.62 0.37 0.69 9 0.57 0.34 0.63 934 0.55 0.33 0.61 Concrete Strength,SOW psi 102 81/1 0.76 0.48 Inner 0.30 91/2 0.68 0.41 Inter 0.27 101/4 0.62 0,37 inner 0.25 Circular Circular Circular Plus El- 0.46 Plus Et- 0.41 Plus EI- 0,37 1 liptical liptical liptical 108 9 0.85 0.51 Inner 0.34 10 0.78 0.48 Inner 0.30 10;1� 0.70 0.42 Inner 0.28 Circular Circular Circular Plus El- 0.51 Plus Ei- 0,48 Plus El- 0.42 114 • Iiptical A llplieal liptleal 120 A 126 ^ A A 132 ' A ... ... 138 A A ... ... ... ... .. ... ... ... ... ... A 144 A A ... A For modified or special designs see 7.2 or with the permission of the purchaser utifiz°the provisions of Specification C 655.Steel areas may be Interpolated between those shown for variations In diameter,loading,or wall thickness.Pipe over 96 in,in diameter shall have two circular cages or an Inner circular plus one elliptk.sl cage. °For these classes and sizes,the minimum practical steel reinforcement is specifled.The actual ultimate svength to greater than the minimum strength specified for nonreinforeed pipe of equivalent diameters In Specification C 14. 'As an alternative to designs requiring both Inner and outer circular cages the reinforcement may be Positioned and proportioned In either of the tdlowing manners: An inner circular cage plus an elliptical cage such that the area of trio elliptical cage shalt not be less than that spodhAd for the outer cape In the table"the total area of the inner circular cage plus the elliptical cage shall not be lass than that specified for the Inner cage In the table. An inner and outer cage plus quadrant mats In accordance with Fig, 1,or An inner and outer cage Plus an elliptical cage in accordance with Fig,2, °Elliptical and quadrant steel must be held.itt place by meant of holding rods,ehalrs,or other positive means througrqut the entire casting operation. `As an alternative,single cage reinforcement may be used.The reinforcement area In square In.per linear foot srtas be 0.20 for wall B and ope for watt C. s Three-edge•b,earing test to ultimate load Is not required fa any class of pipe 60-in.or less In diameter provided aU other requirements of this specification are met. circumferential reinforcement shall be as prescribed for request approval by the purchaser of modified designs that Classes I to v in Tables 1 to 5, except as provided in 7.2. differ from the designs in 7.1; or special designs for sizes and 7.1.1 Footnotes to the tables herein are intended to be loads beyond those shown in Tables 1 to 5, 7.1, or special amplifications of tabulated requirements and are to be designs for pipe sizes that do not have steel reinforcement ' considered applicable and binding as if they were contained areas shown in Tables I to 5 of 7.1. in the body of the specificatioll. 7.2.2 Such modified or special designs shall be based on 7.2 Modified and Special Designs: rational or empirical evaluations of the ultimate strength and 7.2.1 If permitted by the purchaser the manufacturer may cracking behavior of the pipe and shall fully describe to the 3 08:59 }', U4 W q$�s C 76 TABLE 3 Design Requirements for Class lit Reinforced Concrete Pipe-' NOTE-Sea Section 5 for basis of acceptance specified by the purchaser. The strength test requirements in pounds-force per linear toot of pipe under the three-edge-bearing method shall be either the 0-toad (test load expressed in pounds-force per linear foot per toot of diamotor)to produce a 0.01•in. crack,or the Ddoads to produce the 0.01-In, crack and lie ultimate load as specified below, multiplied by the internal diameter of the pipe in feet, D4oad to produce 9 0.01-in.crack 1350 D-load to produce the ultimate load' 2000 Reinforcement,in?1linear It of pipe watt Walt A Wall B Wall C Internal Concrete Strength,4000 psi Concrete Strength,4000 psi Concrete Strength,4000 psi Oesignated Diameter, Wag Circular wan Circular Wag Circular In. Reinforcement c Eliptical Thick- Reinforcement' Elilptical Thick. Relnforcementc E1iSpitcal Thick Aoinforco- Reinforce Reinforce no moot sses. Inner Outer o nesses. Inlet Outer me.t° passes, Inner Outer mentO In. Cage Cage in, Cage Cage in. Cage Cage 12 1_/. 0.070 ... ... 2 0.079 ... 23A 0.070 1S 17/0 0.076 21/. 0.078 ... 3 0.07, 18 2 0,078 ... 0.07° 21/2 D.07 a ... 0.07 B 3'A 0,078 ... 0.07B 21 21/4 0.14 0.11 23/. 0,078 ... 0.07 a 3t4 0.079 0.079 24 21/2 0,17 0,14 3 0,070 ... 0.078 31/. 0.07 0.078 27 2% 0.18 ... 0.16 31/. 0.16 ... 0,14 4 0.08 ... O.D7° 30 2% 0.19 ... 0.18 31/z 0.18 0.15 41/4 0.10 ... 0.08 33 21/0 0,21 ... 0.20 33/. 0.20 ... 0.17 41/2 0.12 ... 0.10 36 3 0.21 0.13 0,23 4 E. 0.17 0.10 0119 4V. 0.08 0.07 0.09 42 31/2 0.25 0.15 0.28 41h 0.21 0.13 0.23 51/. 0.12 0,07 0.13 48 4 0.32 0.19 0.35 5 0.24 0.14 0.27 64'4 0.16 0.10 0.18 54 4'/2 0.38 0.23 0.42 51/2 0.29 0.17 0.32 61/4 0.21 0.13 0,23 60 5 0.44 0.28 0.49 6 0.34 0.20 0.38 6s/. 0.25 0.15 0,28 66 51/1 0.50 0.30 0.55 61/2 0.41 0.25 0.46 7y. 0.31 0.19 0.34 72 6 0.57 0.34 0.63 7 0.49 0.29 0.54 7V. 0.36 0.22 0,40 Concrete Strength.5000 psi 78 61/2 0.64 0.38 0.71 71/2 O.S7 0.34 0.63 81/6 0.42 0.25 047 84 7 0.72 0.43 0.80 8 0,64 0.38 0.71 BY. 0.50 0.30 0.56 Concrete Strength,5000 psi Concrete Strength,5000 psi 90 71/2 0.81 0.49 0.90 81h 0.69 0.41 0.77 91/. 0,59 0.35 0.66 96 8 0.93 0.56 1.03 9 0.76 0.46 0.84 9% 0,70 0.42 Inner 0.28 Circular Plus E6 0.42 liplical 102 81h 1.03 0.62 Inner 0 41 91h 0,90 0.54 inner 0,36 10'/4 0.83 0.50 Inner 0.33 Grcular Circular Circular Plus Ef- 0.62 Plus EJ- 0,54 Plus El- 0.50 optical Apical npticat 108 9 1.22 0.73 Inner 0.49 10 1.08 0.65 Inter 0,43 103/. 0.99 0.59 inner 0.40 Circular Circular Circular Pius Et- 0.73 Plus El- 0.65 Plus El- 0,59 fiptical optical llptical 114 ... A A 120 A ... ... ... ... " A ... ... 126 A A A 132 A ... ... A ... ... 138 " A ... ... ... ... A ... ... 144 A A A "For modified of special designs see 7.2 or with the permission of the purchaser utilize the provt:ionz of Specificatlon C 655.Stool areas may W Intwpolsted between thosa shown for variations in diameter,loading,or wall thickness.Pipe over 96 in.In dlametar shall have two circular cages or an Inner circular plus one elllptical cage. °For these daises and sizes,the miniertum practical steel reinforcement Is specified.The actual ultlmaw strength is greater titan trio minimum strength specified for nonrelnforeed pipe of equivalent diameters in Specification C 14. °As an alternative to designs requiring both inner and outer ciradar rages the reinforcement may be positioned and proportioned in either of the following manners: An inner circular cage plus an elliptical cage such that the area of the elliptical cage shall not 159 loss than that specified for the outer cage in the table and the total area of the inner circular cage plus the ottiptical cage shall not be less titan that spediled for the Winer cage In the table. An Inner and outer cage plus quadrant mats In accordance with Fig.1,or An inner and outer cage plus an elliptical cage in accordance with Fig.2. °Elliptical and quadrant steel must be held in place by means of holding rods,chairs,or other positive means throughout the entire casting operation, t As an alternative,single cage reinforcement may be used.The relnfercament area in square In.per linear toot shall be 0.30 for wall 8 and 0.20 for wall C. mil �TTroo-cdgo-b 6,,9 to3t to lira„aid road is not required for any class or pipe 604m.or less In diameter provided an other requirements of this specification are met. 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GIs - - 11!JhJE1111111111111111111111111111 ��C� ; 11©111�!IIGI�!!��111111111111111111111 ,� ��1�!! : - 111l1111*111111111111111111111111 e�i�G� : ,. 1�1�'��!-IIShJ111111 1111111111111111 �C���� 11��11l11l�1�'11111 1111111111111111 �� . .: � 1111l�I�J111�1111111'���1111■�11111 MINIMh1UIIIIIGI/�IIIIIIIIIII���1 111111111911111II(�111111111111111 �e�� , Is1!111�11�!IIII�IIIII� i1.��ililEll �® � IJ!�'lllllh������■I11111►i��1111111E�1� ®�®�� Illllll�iii%��� 1®1111111��11111111'!` �� ; �� e1111111����'�'°���1111C01111111111�1 ���� , 11111111111111111111'I�IINillllill. 1111191pill1 MINE 11 1111111111 - Oi 11111 IIIIN11111111111111111111111 11111 IIIIIIIIIIIIIIIIIIIl11111111� � 11 1111111111111111111111111111111 5��� 1111111111111111111111111111111 1111111111 111111111111111111111111 ���� 1111111111 111111111111111/1111111 IIIIN111111111111111111►11111111� © E N T R A N C O o VEY ' MAR 17 1993 CITY OF RENTON Engineering Dept. Houser Way North Renton, Washington REGIONAL DRAINAGE ANALYSIS Prepared for tCity of Renton i Prepared by ENTRANCO ' 10900 NE 8th Street, Suite 300 Bellevue, Washington 98004 (206) 454-5600 January 1993 CITY OF RENTON MEMORANDUM DATE: March 17, 1993 TO: Dave Jennings FROM: Joe Armstrong SUBJECT: Houser Way ielocation (Regional Drainage Analysis) Attached for your file is a copy of the completed "Regional Drainage Analysis" for the above subject project. ENTRANCO will be starting the Phase 1 design in about two months or sooner. As part the scope the consultant will expand on the previous analysis. ' CONTENTS Page INTRODUCTION 1 ' MODELING 1 ' CURRENT CONDITIONS 6 EFFECT OF HOUSER WAY PROJECT ON STORMWATER SYSTEMS Drainage Requirements g IMPROVEMENT ALTERNATIVES ' Description of Alternatives g Cost of Alternatives 12 ' Cost Reduction Options 13 ' RECOMMENDATIONS FOR FURTHER STUDY 14 REFERENCES 14 ' APPENDIX - Planning Level Cost Estimate ' 91024 i REPORTS I REGDRAIN(1127/93)1 ahw ) ' FIGURES Page ' 1. Vicinity Map 2 2. Flow Comparison Points 4 3. Schematic of Pipe System Modeled with EXTRAN 5 ' 4. Conceptual Drawing of North Houser Swale 10 ' TABLES Page ' 1. Current Conditions of Houser Way North Drainage System 7 2. Comparison of Houser Way North Alternatives: 100-Year Storm 11 ' 3. Comparison of Houser Way North Alternatives: 25-Year Storm 13 ' 910241 REPORTS/REGDRAIN(1/27193)1 ahw II HOUSER WAY REGIONAL DRAINAGE ANALYSIS ' INTRODUCTION ' This report describes the results of a hydrologic and hydraulic modeling effort to verify the existing conditions in the vicinity of the proposed Houser Way Relocation ' Improvements project and to analyze options for regional runoff conveyance in that area. The project area runs parallel to and just west of 1-405 in Renton, Washington (figure 1). Planned improvements will extend Houser Way through currently vacated right-of-way from North 8th Street south to Sunset Boulevard, resulting in loss of both an existing wetland and an open channel. Runoff from developed upland areas is con- veyed through the Houser Way area on the valley floor, by way of the open channel in the Houser Way right-of-way or through one of a number of pipes along the hillside, and is eventually discharged to Lake Washington. Entranco refined an existing EXTRAN storm sewer model of the region to provide increased detail within the project ' area, and used the refined model to analyze how the stormwater is conveyed through the existing system. Using the results of the model runs, three alternatives to mitigate the expected changes in the system due to the Houser Way project were evaluated ' and costs determined for the three alternatives. It is important to note that this analysis focuses on the Houser Way project as it impacts ' regional drainage patterns. Project impacts on site drainage, such as increased runoff and need for detention and treatment, are beyond the scope of this report and would require further analyses. MODELING ' The hydrology of this basin had been characterized in earlier studies En r Y 9Y s ( t anco 1991). For the Houser Way analysis, two changes were made in the hydrological calculations to further refine this analysis. First, the drainage basins around Houser Way were fur- ther subdivided into several subbasins and the flows for the design storms were calcu- lated for these subbasins. Hydrographs for all subbasins were determined using the King County method, as delineated in the King County Surface Water Design Manual (1990), using 2-, 10-, 25-, and 100-year 24-hour rainfalls of 2.0, 2.9, 3.4, and 3.9 ' inches, respectively. The second refinement was to extend the Houser Way area stormwater conveyance systems in the model to capture flows from more individual subbasins on the hillside to the north and east of the site. The net result of these im- provements is to more accurately model the function of the systems in the immediate vicinity of Houser Way. ' 910241 REPORTS/REGDRAIN(1/27/93)/ahw 1 r rr r r r r r rr �r r �w rr rr rr err rr ur rr r� `S . .. o m shall uck Ave r O c tt O x 3 ,srar'� 0 -Wh l ortl to Ave S r. 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Iv7 Z `o NE i ce PL v 3S'3A 76 [�n7} x n a't9,d Pier[e 4 _ to r" n NE ✓` 3g anV 9Z1 y •< n y SF y trl _t0 ' `! — t Gt`Nn AV to - ve JE n1I AV E vi CA o �_tn 'it7AK1111 O ludmond ve NE .o _` z o {le dzn in ttond inm w rt+ z z �Z licit 2 All n 311 anJ I,J,+. d' in Shelton m PF m in s D ''m• n T.comae Q0 " ; �. 2 Ave S r Urten�n Wfi P rn ` NE m� _` U on "'Iton N jz. zm v NEzE. -ad m '^ m m n z C( Vasho l N Vashon ,_+: a p Jt �' CrS °ysct• n ((/n, v t7 r o r CT rn z n^,o AV UWhlhnan, -t -i � �i II an '1 a in ~p �zz rn � A :orl 7 's o Ave 1t S r^ a SE fan:nrer.i,,r 13fi Ave m m By�ynoAon. N z n z m m m ti u, In previous studies this EXTRAN model had been used to evaluate this area and had been able to reasonably match the observations made during the January 9, 1990 ' storm, a recent storm event with a recurrence interval of around 25 years. The model of that particular event predicted water levels at North 8th Street and Garden Avenue North which matched observed levels, and predicted flooding in the places where flooding was observed during the storm. The current model formulation was improved by the inclusion of information from recent surveys conducted by Tudor Engineering and SSOE. ' Two assumptions were made concerning the condition of the lower section of the drainage system. First, the open channels which start south of Lake Washington Boulevard and travel through Gene Coulon Memorial Beach Park, hereafter referred to as the "pond system" (see figure 2), were assumed to be well maintained and free of overgrown bushes. This results in a lower resistance to flow than would occur if the 1 ponds were not maintained. The effects of the assumption of maintained channels were tested using a King County synthetic 25-year storm event. Flows through the ' channels with unmaintained sides were predicted to be about 5 percent less than the maintained flows. The maximum flow through the Garden Avenue North lines was 15 percent less for the unmaintained model, and water levels at North 8th Street and Garden Avenue North were predicted to be 0.8 foot higher. Second, the capacity of the culverts connecting the ponds was assumed to be ex- panded as part of mitigation for the PACCAR site development. The added culverts include two 54-inch pipes from the farthest upstream channel (Pond 1) to the next (Pond 2), and one 84-inch pipe from Pond 2 north to Pond 3. These culverts have ' been installed in the system. These two assumptions are critical to the modeling re- sults, as they increase the conveyance through the pond system which, in turn, in- creases the conveyance through the entire stormwater system. The model also included a critical assumption regarding predicted flooding to the east of 1-405. At the uppermost point of the pipe which connects to the North 8th Street storm sewer line from the east, flooding is predicted to occur during high flows. In this version of the model, this point is called junction 1207 (see figures 2 and 3). Due to the formulation of the EXTRAN model, the water which leaves the system as "flooding" disappears from the model, and is artificially lost. Since the flooding was predicted to be significant (over 12 acre-feet for the 25-year storm), an alternate pathway for this ' water was modeled so that the water would not be lost. Based on topographic information and previous studies (City of Renton 1988), it was assumed that this water would appear as street flooding until it reached a swale along 1-405, eventually ' discharging into the channel along the Houser Way alignment approximately one-third mile south of North 8th Street. Field investigations since the modeling was completed indicate that this precise route probably would not be taken, but that overflow would still discharge to the Houser Way North right-of-way via several pipes which cross under 1-405. ' 910241 REPORTS i REGORAIN(1/27/93)/ahw 3 C:OCADOODGN091024-220ENVOFIG8.DGN WASHAKE NGTON Gene Coulon Memorial Beach \ m 0 1/8 1/4 Pork o 0 MILE 1 I W M \ < N Pond 5 � 1 pipe 401 � • NE 12th ST ♦♦ LEGEND •' '♦rr r ■on's Existing Plpe System Pipe 154 •� 900 Pond System 900�' • Pipe 430 •• ® Areas of Modeled Flooding � �'•• ■ • • Z • 405 w Pipe 152 Pipes : < • '. 102 3 603 Z ■ G� ■ y � w • w • d i p o O w • G m zG a 01 z Z w 2 a N 8th ST ,......... ......... as lose Y Q 1 Pipe 201 LLJ n O v G Z N 5t ST a ' z \ w 0 N j4t ST \ 1.41 � J2 _j. ❑ � 405 HOUSER WAY REGIONAL DRAINAGE ANALYSIS ' Figure 2 E N T R A N C O FLOW COMPARISON POINTS 4 ' LAKE TA5HIN67ON ' LEGEND o PIPE J UNGT I ON 5�2 ® 5TORA6E JUNCTION 5001 ' 2ow JUNGT I ON NLWER `M 400 1 PIPE/OPEN CHANNEL 3002 INFLOW OR OUTFLOW 3001 2002 1 404 1001 2001 F 1401 14OZ 1403 /1150 1460 1 1406 461 II00 I405 1601 1430 1 450 1 95 1 F IIOI 1952 ' 1602 1431 I432 1433 C 1453 1 1 5 1 I 102 1603 1434 m 1454 F 1152 1103 1604 1 435 A 1 1 04 1605 D ' 1936 GN 1 606 ^ „ 1153 1105 IUt�\VII � 1607 1437 Z 1439 1106 m 60 16 1438 4- 11 54 1107 Z 1609 1 7 1 1 174 I 1792 NOT TO SCALE 1106 m 1 (4 0 F I I o9 Z 1 6J 1 1 7 1 0 1790 II99 1699 � o 0 0 16J 2 1201 1202 1203 F 1300 f 0'00 ► 3o I N.Sti\. St. 750 1 25 3 1 35 1 1 302 _ b b b 1 Z5Z 135Z 1 303 1601 1 353 1 629 185G 1 700 1 Z5 I 1304 1802 1643 1250 1 305 1 603 0 1 657 1044 CEDAR o "' " "' " "� ► 306 1604 1645 1 656 1 730 RIVER 1 307 1 do5 1 659 1 326 1 31 9 160G 1 647 1�� 1 640 1 327 1 3Z0 1 607 16G I 1326 132 I i 606 1662 IWLOrI ON VALLEY ' o = f=LooK D 15TR I MUTED 0 o I dG QU 3 EdLLY TO JLMLT I CtJS IN VICINITY. 1644 1 6G 5 :A 0,10I,or 6, 199Z HOUSER WAY NORTH REGIONAL DRAINAGE ANALYSIS ENTRANCO Figure Schematic of Pipe System Modeled with Extran 5 ' Although this assumption is based on precedent and results in a more reasonable simulation than had the loss of stormwater volume been ignored, it must be refined before the final design of any system along Houser Way. Also, it is unlikely that all of the predicted flooding would occur at this point. The pipe systems further upstream were added to the EXTRAN model in an effort to check the functioning of the pipe sys- tem. The model predicted these pipes to be overloaded, resulting in flooding which de- creases the flow which actually reaches junction 1207. This may indicate that there is some attenuation of high flows within the pipe system in the east basins, and that the actual flows to junction 1207 are somewhat lower than the modeled flows. The hydrog- raph method used is unable to take into account such attenuation, but the modeled re- sults can be assumed to represent a worst case scenario. CURRENT CONDITIONS Predicted water levels and pipe flows at various storm recurrence intervals for the exist- ing conditions model runs are shown in table 1. It is important to note that these re- sults are not necessarily comparable to observed storm events, as planned upgrades to the system were included in the model. In addition to the assumed upgrades to the pond system, the conveyance through the system is upgraded by the completion of the ' 72-inch line down Garden Avenue North. This line greatly increases the flow capacity to the pond system, and the net result of all of the improvements is a lessening of the backwater conditions which have led to street flooding in the past. The predicted depth of the stormwater in the system (which limits the capacity of the upstream pipes) is shown for two important locations: the PACCAR outfall at North 8th Street and Garden Avenue North (junction 1000) and Pond 1 (junction 1001). Under the modeled current conditions, the North 8th Street line reaches capacity during rainfall events approximately the size of the 10-year, 24-hour storm. Instead of passing larger flows, this pipe serves to create a restriction on the pipes entering the system at ' the intersection of North 8th Street and Houser Way, and introduces a backwater situ- ation upstream. The pond system, on the other hand, does not appear to reach capac- ity even during the 100-year storm. However, the increasing levels in the ponds do ' begin to show backwater effects on the pipes coming in from Garden Avenue North and the North Basin for the larger storms, as shown by the "plateau" of peak flows in these systems. 91024/REPORTS/REGDRAIN(1/27/93)/ahw 6 ' Table 1 Current Conditions of Houser Way North Drainage System Storm Recurrence Interval (years) 2 10 25 100 Design Flows 1 Water level (ft) at PACCAR Outfall at ' North 8th St./Garden Ave. N 2.71 3.14 3.33 3.36 Pond 1 3.16 3.96 4.31 4.49 Flow (cfs) North 8th St. 76.9 82.7 82.9 82.9 39.7 - 79.7 Garden Ave. N (54-inch) 24.3 37.8 47.0 49.0 58.2 - 108.2 Garden Ave. N (72-inch) 87.9 149.9 146.8 155.4 72.8 - 351.3 North Basin (pipe 401) 49.8 83.1 89.8 90.4 74.5 ' North Houser (pipe 430) 13.0 17.9 20.9 25.6 46.4 Pond system 204.4 276.7 316.7 343.9 174.6 - 1,709.4 Houser Open Channel 31.4 124.1 128.8 128.9 101.0 1. Theoretical design flows using Manning's equation. These assume open-channel flow and do not reflect surcharged conditions or downstream constraints. The ranges of flows reflect minimum and maximum designed for the different pipes in the system. The EXTRAN model also shows the amount of water which flows out of the system as flooding. Upsizing of the culverts in the pond system does not seem to change mod- eled street flooding relative to the preimproved model runs. The flooding at the Houser ' Way underpass is estimated at 0.1, 0.7, 1.4, and 2.5 acre-feet for the four design storms. No flooding is predicted along Garden Avenue North, where most of the re- gional stormwater flows to the pond system. However, the backwater conditions ' caused by the North 8th Street pipe do lead to a large amount of flooding at North 8th Street and Houser Way (1.1, 8.1, 13.9, and 22.7 acre-feet). Areas of predicted flooding ' are shown in figure 2. As noted before, one of the critical assumptions for this model- ing was that the overflow water from the area on the hillside is routed to the channel along Houser Way. It is primarily this flow which seems to result in the flooding in the 1 vicinity of the intersection. Again, it is not certain how much of this flow is actually at- tenuated in the systems on the hillside. Any attenuation would probably lead to lower predicted flooding on the valley floor. In comparison, the 25-year storm for the existing conditions without the larger pond cul- verts (but with the assumption of maintained ponds) predicted 1.2 acre-feet of flooding at the underpass, 11.7 acre-feet at North 8th Street/Houser Way and 2.8 acre-feet on the hillside, although this run produced 10 percent less flow in the system than the im- proved condition run. The flow is less because this run used SWMM Runoff Block ' 910241 REPORTS/REGDRAIN(313193)1 jcw 7 modeling to determine the hydrographs, and this accounts for attenuation more than does the SBUH hydrographs. It is important to remember that flooding in this system is dictated both by high water levels downstream from the flooding areas and by high flow levels. Under the Houser Way underpass, the highest flow conveyed without flooding was predicted to be 82 cfs, which is approximately the peak flow of the 10-year storm. Likewise, the maximum predicted conveyance through the North 8th Street pipe is about 96 cfs before flooding, which is the flow predicted for the 10-year storm. However, with higher water levels at the outlet, these same flows would cause flooding, and less flow could be safely con- veyed. Because of the water level/flow interaction, it is difficult to establish flow levels above which flooding will occur for any one specific pipe section. EFFECT OF HOUSER WAY PROJECT ON STORMWATER SYSTEMS ' On a regional level, the effect of the Houser Way road improvement will be to alter an area along the railroad tracks south of North 8th Street, which currently serves as an open channel for storm flows. It is probable that, in order to construct the roadway, this channel will need to be replaced by an underground pipe. The drainage alternatives considered involve converting the channel to a pipe and providing some other im- provements to the system. Drainage Requirements The City of Renton drainage requirements are the same as those defined in the King County Surface Water Design Manual. For this study, Core Requirements 1-4 apply, as paraphrased and discussed below: 1. Runoff "must be discharged at the natural location". The intent of this requirement is to ensure that baseflows of streams are not changed by drainage changes, so the flow between pipes within a stormwater system is of lesser concern. Depending on interpretation, the natural location for discharge from this area could be consid- ered to be at a specific point within the stormwater system, at Pond 1 or at Lake Washington. Since the entire system from Houser Way to Pond 1 consists of piped storm drains, the natural discharge of this system reasonably can be assumed to be considered to be at Pond 1, which is the assumption used for this analysis. 2. Upstream and downstream areas which would be impacted by the changes to the drainage system must be analyzed. This study would presumably fulfill much of the analysis requirement. 91024/REPORTS/REGDRAIN(1/27193)/ahw 8 ' 3. Restrict postproject peak flows to preproject levels. The regional analysis does not consider an increase in the amount of runoff generated in the project area, but this requirement applies in that the 100-year, 24-hour peak flow after improvement will be constrained to be no more than 0.5 cfs more than the pre-improved 100-year flow. Also, some regional biofiltration may be required as part of the Houser Way project to replace that occurring in the existing channel. 4. New pipe systems are to be designed to convey the 25-year peak flow. The pipes for this study were designed for such a rate, although, as mentioned earlier, those flows will have to be confirmed before final design. IMPROVEMENT ALTERNATIVES ' Description of Alternatives Three alternatives were considered to improve the functioning of the Houser Way drainage system. For this analysis, we assumed that: • Road placement will require filling the channel. • A 72-inch pipe will be necessary to convey the modeled flows. • Four 400-foot-long sections of 72-inch pipe will be set at the slope of the exist- ing ground surface. Alternative 1 is to replace the 42-inch pipe under North 8th Street with a 72-inch pipe. Alternative 2 is similar to this, but also involves removing the cross connection between ' the 54-inch and the 72-inch lines at North 8th Street and Garden Avenue North. Alternative 3 is to build a 10-foot wide swale and 48-inch overflow pipe along Houser Way North, north of North 8th Street, to divert some of the flows from the North 8th Street line and pick up drainage from the hillside. A conceptual drawing of this alter- native is shown in figure 4. The swale would have the same surface overflow rate as the existing channel for the 2-year flow, giving it comparable biofiltration capacity, as biofiltration is dominated by physical (settling) processes. The resulting predicted flows and water levels under each of these alternatives for the 100-year storm are shown in table 2. Replacement of the open channel with a 72-inch pipe is not expected to affect the drainage system compared to existing conditions. However, the existing flooding also continues, as well as the existing conveyance, so the replacement cannot be consid- ered to be a drainage improvement. 91024/REPORTS!REGDRAIN(1/27/93)/ahw 9 •:$�o. III e O e 0 s — •. HGUSER WAY N 6WALE BYPAS`�/GV�RFLGW PIPE ' HOUSER WAY NORTH REGIONAL DRAINAGE ANALYSIS ENTRANCO Figure Conceptual Drawing of North Houser Swale 10 Table 2 Comparison of Houser Way North Alternatives 100-Year Storm Alternativesl 72-Inch Existing Pipe 1 2 3 Only Height at junction (ft) PACCAR Outfall at North 8th St./Garden Ave. N 3.36 3.36 7.07 5.51 3.39 Pond 1 4.49 4.50 5.03 5.15 4.68 Flow (cfs) North 8th St. 82.9 82.8 204.6 211.0 82.8 Garden Ave. N (54-inch) 49.0 47.5 73.3 63.4 66.5 Garden Ave. N (72-inch) 155.4 155.2 161.6 190.5 148.8 North Basin (pipe 401) 90.4 90.5 86.4 86.3 89.7 North Houser (pipe 430) 25.6 27.1 28.2 28.6 47.4 Pond System 343.9 342.9 411.4 424.8 366.4 Houser Channel 128.9 128.6 129.4 129.4 129.0 1. Alternative 1 is the North 8th Street upgrade. Alternative 2 is the North 8th Street upgrade with removal of the cross-connection at North 8th Street and Garden Avenue North. Alternative 3 is the bypass Swale. Alternative 1, increasing the size of the North 8th Street pipe, leads to increased con- veyance and reduced flooding throughout the system, eliminating the flooding at North 8th Street and Houser Way North with only a minimal (0.08 acre-foot) amount of flood- ing on Garden Avenue North. One major drawback for this option is that it leads to ' greatly increased water levels at the intersection of North 8th Street and Garden Avenue North (junction 1000), where drainage from the PACCAR site enters the sys- tem. The higher water levels could lead to restricting the flow of water off of that site and result in further flooding. In fact, the predicted flooding on the PACCAR site in- creases from 0.55 acre-foot to 2.0 acre-feet due to the enlarged pipe system. ' Alternative 2 improves on Alternative 1 by removing the cross-connection between the Garden Avenue North lines at North 8th Street. The result is increased conveyance through the two Garden Avenue North systems (a total of 254 cfs vs. 235 cfs, 204 cfs for existing) and down the North 8th Street line while the water level at the PACCAR outfall is 1.5 feet lower than in Alternative 1. This alternative does lead to some 91024/REPORTS/REGDRAIN(1/27193)1 ahw 11 flooding (0.5 acre-foot) from the North 8th Street line, and the water level at junction 1000 is still 2.15 feet higher than under the existing conditions. However, the predicted increase in flooding on the PACCAR site is only 0.15 acre-foot. Alternative 3, the bypass swale, like the first two alternatives, also reduces the pre- dicted flooding at North 8th Street and Houser Way North, although it does not elimi- nate that flooding. Additionally, it results in a slightly improved conveyance down Garden Avenue North, but does not affect the maximum flow down the North 8th Street line. Overall conveyance through the system is improved by about 23 cfs, and there is no effect on flooding on the PACCAR site. As mentioned above, the swale would re- produce the biofiltration from the existing channel, but there are some uncertainties re- garding this option, including the size of swale which can be built in the space available. This alternative could provide additional wetland functions which may be required as mitigation when the wetland is removed. These alternatives were run for the 25-year storm as well, and the results are shown in table 3. One of the more important results for the 25-year storm analysis is that ' Alternative 2 does not lead to increased flooding on the PACCAR site for this storm. It is possible that other drainage alternatives may achieve the same results, such as replacing one large pipe with two smaller ones, but these three alternatives were con- sidered the most viable. A concern about increasing the conveyance through the system is that increases in peak flows will lead to a requirement to provide detention. It is unknown whether the area exists to provide the detention for these alternatives, which would increase the peak flows through the pond system by as much as 82 cfs. The cost for such a facility in this area could be expected to be significant. ' Of the three alternatives evaluated to improve drainage in the vicinity of Houser Way, Alternative 2 appears to be superior to Alternative 1, as the removal of a cross connection seems to improve drainage in the Garden Avenue North lines. Alternative 3 does not reduce flooding as much as the other two, but it provides biofiltration and does not affect the drainage off of the PACCAR site. Cost of Alternatives A planning level cost analysis was conducted for the three alternatives. The costs for Alternatives 1 and 2 were the same ($1,996,000), as the cost of removing the cross connection was assumed to be negligible. Alternative 3 would cost $2,824,000. These are planning level costs, and are subject to change before final design. The calcula- tions for these costs are shown in Appendix A. ' 910241 REPORTS!REGDRAIN(1127i93)I ahw 12 Table 3 Comparison of Houser Way North Alternatives 25-Year Storm Alternatives' 72-Inch Existing Pipe 1 2 3 Only Height at junction (ft) PACCAR Outfall at North ' 8th St./Garden Ave. N 3.33 3.34 6.95 5.08 3.20 Pond 1 4.31 4.30 4.89 4.98 4.44 Flow (cfs) North 8th St. 82.9 82.9 209.0 203.2 82.7 Garden Ave. N (54-inch) 47.0 48.9 73.5 62.0 42.0 Garden Ave. N (72-inch) 146.8 149.1 169.1 188.9 153.8 North Basin (pipe 401) 89.8 90.0 86.0 85.9 89.4 North Houser (pipe 430) 20.9 20.9 21.1 21.3 39.6 Pond System 316.7 321.3 391.9 402.2 335.9 ' Houser Channel 128.8 117.1 117.1 117.1 117.1 Flooding (acre-ft)2 ' Houser& North 8th St. 13.9 15.6 0.0 0.0 5.4 North Houser 1.4 1.5 1.5 1.5 2.3 PACCAR Site 0.3 0.3 0.5 0.3 0.3 1. Alternative 1 is the North 8th Street upgrade. Alternative 2 is the North 8th Street upgrade with removal of the cross-connection at North 8th Street and Garden Avenue. Alternative 3 is the bypass ' swale. 2. See figure 2 for locations. Cost Reduction Options Entranco also investigated conceptually various options to reduce the high costs of these alternatives while providing equivalent drainage functions. ' It is important to note that most of the predicted peak flow in the planned 72-inch Houser Way North pipe is due to the overflow from the eastern basin. Without this overflow, the peak flow through the channel would be reduced by more than 60 per- cent-a 42-inch pipe may be sufficient to convey the flows. The eastern overflow could 910241 REPORTS/REGDRAIN(1127/93)1 ahw 13 ' be reduced by installing a regional detention facility on the hillside. It is estimated that using a 42-inch pipe along Houser Way would save about $440,000. ' A second cost-saving option would be to use two smaller pipes instead of one large pipe to improve the system. Using a 42-inch and a 48-inch pipe along Houser Way North would save $115,000 in material and excavation costs, and installing a 48-inch pipe parallel to the existing system along North 8th Street would save $310,000 over replacement with a 72-inch pipe. ' It appears that the most economical measure would be to develop a regional detention facility, as it may be eligible for cost-sharing with other agencies. This would allow ' downsizing of conveyance facilities through the project while possibly reducing the flows and flooding in the valley area. ' RECOMMENDATIONS FOR FURTHER STUDY ' There are at least two drainage issues regarding the Houser Way Improvement project which will be important to clarify when proceeding with that project. The first is the pre- viously mentioned drainage/overflow off of the hillside, and the resulting flooding on the ' valley floor, the amount of which must be verified before final design. The second issue is that a portion of the project area currently drains to a bypass pipe which runs through the PACCAR site. Since the flow through the bypass is limited, peak runoff flow rates ' may be restricted and additional detention may be required in that part of the site. ' REFERENCES Entranco ' 1991 Garden Avenue Drainage Study. Prepared for PACCAR, Inc. October 1, 1991. City of Renton 1988 North Renton Basin. Interim Drainage Study to Address Development West of 1-405. May 1988. ' 91024/REPORTS/REGORAIN(1127/93)1 ahw 14 Appendix ' PLANNING LEVEL COST ESTIMATE 1 SHEET NO. / OF Z ENTRANCO ENGINEERS, INC. JOB NO. PROJECT _�/�,�sr-,2 L✓A �/ ' - CALCULATIONS FOR r s C-� c r / a ;r= - /� A tl'V i� MADE BY DATE 6z q CHECKED BY AMR- DATE00 3-�z ram-; - - 00. O o v�"RSIov/o TNc2 V,4UC7 1 L=A 3C�� C�C�O r �0., 0 C�C7 . . --- _.. 00 T- Tom CA. ; 000 - _- y.�, ov.0 _ _ S2 _ oo PA VT I''ATcI1 — . . // S S C1-, - CA o '. r 1 sty Z.L.S�o 0 13 rc i A Tl0/L/ ��. 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The active flood storage volume provided by the project is 1.25 acre-feet, which is greater than any of the "Target Design Volumes" calculated. E N T R A N C O t Houser Way North Renton, Washington REGIONAL DRAINAGE ANALYSIS Prepared for ' City of Renton Prepared by ENTRANCO 10900 NE 8th Street, Suite 300 Bellevue, Washington 98004 (206) 454-5600 January 1993 E N T R A N C O ' Houser Way North Renton, Washington REGIONAL DRAINAGE ANALYSIS Prepared for ' City of Renton Prepared by ' ENTRANCO 10900 NE 8th Street, Suite 300 ' Bellevue, Washington 98004 (206) 454-5600 January 1993 ' CONTENTS Page INTRODUCTION 1 ' MODELING 1 CURRENT CONDITIONS 6 EFFECT OF HOUSER WAY PROJECT ON STORMWATER SYSTEMS Drainage Requirements 8 ' IMPROVEMENT ALTERNATIVES ' Description of Alternatives 9 Cost of Alternatives 12 ' Cost Reduction Options 13 RECOMMENDATIONS FOR FURTHER STUDY 14 REFERENCES 14 ATTACHMENT A-1 - Planning Level Cost Estimate 91024/REPORTS/REGDRAIN(t/27/93)I ahw ( ' ' FIGURES Page ' 1. Vicinity Map 2 2. Flow Comparison Points 4 ' 3. Schematic of Pipe System Modeled with EXTRAN 5 ' 4. Conceptual Drawing of North Houser Swale 10 ' TABLES Page 1. Current Conditions of Houser Way North ' Drainage System 7 2. Comparison of Houser Way North Alternatives: ' 100-Year Storm 11 3. Comparison of Houser Way North Alternatives: ' 25-Year Storm 13 91024/REPORTS/REGDRAIN(1/27/93)/ahw )( ' HOUSER WAY REGIONAL DRAINAGE ANALYSIS INTRODUCTION ' This report describes the results of a hydrologic and hydraulic modeling effort to verify the existing conditions in the vicinity of the proposed Houser Way Relocation Improvements project and to analyze options for regional runoff conveyance in that area. The project area runs parallel to and just west of 1-405 in Renton, Washington (figure 1). Planned improvements will extend Houser Way through currently vacated ' right-of-way from North 8th Street south to Sunset Boulevard, resulting in loss of both an existing wetland and an open channel. Runoff from developed upland areas is con- veyed through the Houser Way area on the valley floor, by way of the open channel in the Houser Way right-of-way or through one of a number of pipes along the hillside, and is eventually discharged to Lake Washington. Entranco refined an existing EXTRAN storm sewer model of the region to provide increased detail within the project ' area, and used the refined model to analyze how the stormwater is conveyed through the existing system. Using the results of the model runs, three alternatives to mitigate the expected changes in the system due to the Houser Way project were evaluated ' and costs determined for the three alternatives. It is important to note that this analysis focuses on the Houser Way project as it impacts ' regional drainage patterns. Project impacts on site drainage, such as increased runoff and need for detention and treatment, are beyond the scope of this report and would require further analyses. MODELING ' The hydrology of this basin had been characterized in earlier studies (Entranco 1991). Y 9Y For the Houser Way analysis, two changes were made in the hydrological calculations ' to further refine this analysis. First, the drainage basins around Houser Way were fur- ther subdivided into several subbasins and the flows for the design storms were calcu- lated for these subbasins. Hydrographs for all subbasins were determined using the ' King County method, as delineated in the King County Surface Water Design Manual (1990), using 2-, 10-, 25-, and 100-year 24-hour rainfalls of 2.0, 2.9, 3.4, and 3.9 ' inches, respectively. The second refinement was to extend the Houser Way area stormwater conveyance systems in the model to capture flows from more individual subbasins on the hillside to the north and east of the site. The net result of these im- provements is to more accurately model the function of the systems in the immediate vicinity of Houser Way. ' 91=4/REPORTS/REGORAIN(1/27/931/ahw 1 C Ave r n n O '�-1 '•F' y- O o Shall tick c ly x N 4Y1111 ortl rn Ave u S r x ml < IG C to z • M 9 Aonlf " Ave S R � � 'Y � 1F-'' tt C) (7 A i Sm hers- Ave -1 S �' W _ Z D CD ° i3 UI 5 Oan Ave 11 r" p 1 ins u t, a Ilams =Ave N s I F z m Jn 1 Ave 2 O - ells ? Ava r.• 00 Z Main Z A o Pell Ave n ►•� - +^ u a�e� •n I MITI ve n Perk ZAve N Park O+I�aelA ,e` (L I:r rt. H col ` z W = Ranlon n Ave S o¢" 1 Y4/• Gordan `'' Ave It Z P° / P^Ig o m nl va S 1A aJow Ave N Galden '-ram.- IA Gre ' y clr 1` Z IA m Ave It �+ N q e _S '� SO y o urn '• �.-� .r- O I hpn Avn U s Ave frC- 1_ -f °�Ave m J� -• '6000 D rn eM u J M m •N m Fe newic AyttlE n s D `m unseJ 91vd 1 ,*? nz, inc"In z .a_,a, ji Vu /i- a Ave. m C ry- in IJunlnrcy Avn Z Ca it 7l SunsaT ' MoNerey +1Arimmey SE. IIE 1� O Z P )n - _ Aberdeen .�' - - Ava „ in Oa' n' ve HE 'n 1 _ uvdc� ve NE [yam Iwr n B Olalna Ave NE f!E ^waine Ave m .Z n a rQ +-� n Camas Avc NE Camas'^ v 1 1y] U1 1 .ate p +D n IC H i v� L ,¢`y¢, -• Oa lon A"a. v flay n J1 Avr: n r 170y1"n ' ti N m 'D fGi ~ o tortknoo L moods Ave N mE -r In IIE ayton _ Fort 1810 z 1r in m Q 1 C I rn nry Ch o Glannwo"r tr 411 F u m f n, lc Z is'o'Ve o _ CJ A NE 1N %, NE " ; _Ave NE D ,.A -SI Iwood , It a rl I I _ Ave r ; •"t e'Itarrl Ion VAve NE �.j 1"JaF C1 kldav A v 1 in ndex Cl Index 1 /• ae •s"v _ �z• n u 9 NF Jefk son m IIE M�` m� D J r/e' n Joltorson, " n r o�� �r Kir land Lene IIE o Z1 ve NE yr o Ave NE ^ Yip m Z.m J 1c1�� 0 4 n w, IInn+ 1r p •¢p Knklan I nnwoud i �, U m 122 AVE N •I YniQ} fl n Monroe Ave NE Ave N i r of C' 1-1N-1 n 21 AVE S rn� Iil ve,p I'1 x to ^+ 17 z<n m m lowpor Z m @ Z rye YZI n M H 1413 mo 4 Z •-r 1 NE m o Uonto e n 3S a�^V�_ m m m rl, na AveHE Av Ave flE Z L h r., 1 N A n v v Sn a� :pC �'g ��;�.b u_� Piorco NE 'E e Pl. m r• y 7`e m + Ill, y E �j In Qj _t'l_ti R I O! .Pn AV - o va a I!E A L1 u Z n ne dmond w � ri O 1uJn,o+Id va NE .) In m p o _ m o m c• m• m o !1 7 r t a CI n Z •n o N w b r1 v.. wl.a 1. . fJ)Z^ 'bellon Ave N. 311 anJ I �-r ' '+ a•l- +n SThellon U �e �1 u m m mY Lm. n 1.canan V.a� .. u ri ��T -+ -1 mJ " n,? Union l 2 Ave S r- v W 1An,AIn ldfv m NE z ,on Z 21 NE z 1lnn1 m z z ,n Z z m -y Cf Vasq n n 1 m Vashu n M m . m m r m r f; v °n Av Fin p m • oUser p1 n o CT i Z n n Whllman+ n n I o CIS ° (; ra `7 _) ! III nail ?� m v z A ^ r° n i 9 ° Z A -.orI r�uoqus a Ave LLap •n ~•--� - r q tiF Ibun+erm iJfi Ave �, y In r IlJyurnun. TZ a in f n `� '� m 17 AVE SE r^r �o .a m in in is �o, ' In previous studies this EXTRAN model had been used to evaluate this area and had been able to reasonably match the observations made during the January 9, 1990 storm, a recent storm event with a recurrence interval of around 25 years. The model of that particular event predicted water levels at North 8th Street and Garden Avenue North which matched observed levels, and predicted flooding in the places where ' flooding was observed during the storm. The current model formulation was improved by the inclusion of information from recent surveys conducted by Tudor Engineering and SSOE. Two assumptions were made concerning the condition of the lower section of the drainage system. First, the open channels which start south of Lake Washington Boulevard and travel through Gene Coulon Memorial Beach Park, hereafter referred to as the "pond system" (see figure 2), were assumed to be well maintained and free of overgrown bushes. This results in a lower resistance to flow than would occur if the ' ponds were not maintained. The effects of the assumption of maintained channels were tested using a King County synthetic 25-year storm event. Flows through the channels with unmaintained sides were predicted to be about 5 percent less than the ' maintained flows. The maximum flow through the Garden Avenue North lines was 15 percent less for the unmaintained model, and water levels at North 8th Street and Garden Avenue North were predicted to be 0.8 foot higher. Second, the capacity of the culverts connecting the ponds was assumed to be ex- panded panded as part of mitigation for the PACCAR site development. The added culverts ' include two 54-inch pipes from the farthest upstream channel (Pond 1) to the next (Pond 2), and one 84-inch pipe from Pond 2 north to Pond 3. These culverts have ' been installed in the system. These two assumptions are critical to the modeling re- sults, as they increase the conveyance through the pond system which, in turn, in- creases the conveyance through the entire stormwater system. The model also included a critical assumption regarding predicted flooding to the east of 1-405. At the uppermost point of the pipe which connects to the North 8th Street ' storm sewer line from the east, flooding is predicted to occur during high flows. In this version of the model, this point is called junction 1207 (see figures 2 and 3). Due to the formulation of the EXTRAN model, the water which leaves the system as "flooding" ' disappears from the model, and is artificially lost. Since the flooding was predicted to be significant (over 12 acre-feet for the 25-year storm), an alternate pathway for this water was modeled so that the water would not be lost. Based on topographic 1 information and previous studies (City of Renton 1988), it was assumed that this water would appear as street flooding until it reached a swale along 1-405, eventually discharging into the channel along the Houser Way alignment approximately one-third mile south of North 8th Street. Field investigations since the modeling was completed indicate that this precise route probably would not be taken, but that overflow would still 1 discharge to the Houser Way North right-of-way via several pipes which cross under 1-405. ' 910241 REPORTS/REGORAW(1/27193)/ahw 3 `} C:4CAODOOGN091024-220ENVOFI GB.OGN LAKE Gene CoulonWASHINGTON Memorial Beach `� a 0 l�g I�4 Park 1 a cl MILE I c� Pond 5 I oPipe 401 i N NE 12th ST L E G E N D mason Existing Pipe System Pipe 154 �900 Pond System Qom• � � Pipe 430 900 ® • Areas of Modeled Flooding �• ; �� Z 405 > Pipe 152 0\ Pipea 0. a :\ 102 S 603 : Z 00 W W a • L. � 2 s � W G m Z a G s i • Z Z �z a � .1 W .I 2 a I N 8th :� ST ���■■�a�a ■���goals IN Eggs I � Q W Pipe 201 n O L. � Z W N 5t ST a z W \ o N 4th ST 2 405 HOUSER WAY REGIONAL DRAINAGE ANALYSIS ' deft E N T R A N C O Figure 2 FLOW COMPARISON POINTS 4 ' LAKE IA5HINCaTCN ' LESEI�D 5002 o PIPE JUNCTION ' ® 'STORAGE JUNCTION 500 I 2coo JUNG T I ON WveR 4M 400 1 PIPE/OPEN CHAMIEL 3002 INFLOW CK OUTFLOW 300I 2002 1404 1 00 1 200 l 1 40 I 1 q0Z F• 1 403 1460. 1406 I t � ! 1 00 / 1 405 ' 1 430 14 1 ,45 1 I L01 _ 1952 1101 I602 1431 1432 1433 O 1453 115 I 1 1 02 1 603 i 434 m 1454 11 52 11 03 I 05 G09 1 935 ;:a1 104 11 G06 1936 > D II 53 It A 1407 1437 Z 1 439 II06 m 1406 I436 11 54 Z I 107 1609 1 7 1 1 174 I 1742 NOT TO SCALE 1 1 as m I u 0 I QI 1740 1109 Z 1710 I 199 I G99 - o 0 0 0 ' 1300 I oco I612 1201 1202 1203 — — — — N.Sth. St. 1 30 I 750 1 253 1 351 1 302 o 0 0 o 125L �-- I 357. 1303 353 I 160 I 1 700 1 25 1 1 309 1602 1629 1 "3 1654, 1250 1305 1603 0 0 0 0 1 6" 1657 CEDAR 1 306 1 604 1 045 1656 1 730 1307 1 605 1 559 R l VER � — — 164c ' 13245 1 31 9 1606 1 647 16G0 1 327 1 320 1 007 166 I INFL01S ON VALLEY 1 32G 1 32 1 1 606 1 642 FLOOR 015TRIDUTY9 l{1 P I bG3 EGUAI.I.Y TO JI.NGT I Q,`i 1644 IN VICINITY, 1 6G5 Octolrar b, 1992 HOUSER WAY NORTH REGIONAL DRAINAGE ANALYSIS ' Figure 3 ® !N T R A N G O Schematic of Pipe System Modeled with Extran 1 ' Although this assumption is based on precedent and results in a more reasonable simulation than had the loss of stormwater volume been ignored, it must be refined ' before the final design of any system along Houser Way. Also, it is unlikely that all of the predicted flooding would occur at this point. The pipe systems further upstream were added to the EXTRAN model in an effort to check the functioning of the pipe sys- tem. The model predicted these pipes to be overloaded, resulting in flooding which de- creases the flow which actually reaches junction 1207. This may indicate that there is some attenuation of high flows within the pipe system in the east basins, and that the ' actual flows to junction 1207 are somewhat lower than the modeled flows. The hydrog- raph method used is unable to take into account such attenuation, but the modeled re- sults can be assumed to represent a worst case scenario. 1 CURRENT CONDITIONS rPredicted water levels and pipe flows at various storm recurrence intervals for the exist- ing conditions model runs are shown in table 1. It is important to note that these re- sults are not necessarily comparable to observed storm events, as planned upgrades to the system were included in the model. In addition to the assumed upgrades to the pond system, the conveyance through the system is upgraded by the completion of the ' 72-inch line down Garden Avenue North. This line greatly increases the flow capacity to the pond system, and the net result of all of the improvements is a lessening of the backwater conditions which have led to street flooding in the past. ' The predicted depth of the stormwater in the system (which limits the capacity of the upstream pipes) is shown for two important locations: the PACCAR outfall at North 8th ' Street and Garden Avenue North (junction 1000) and Pond 1 (junction 1001). Under the modeled current conditions, the North 8th Street line reaches capacity during rainfall events approximately the size of the 10-year, 24-hour storm. Instead of passing larger flows, this pipe serves to create a restriction on the pipes entering the system at ' the intersection of North 8th Street and Houser Way, and introduces a backwater situ- ation upstream. The pond system, on the other hand, does not appear to reach capac- ity even during the 100-year storm. However, the increasing levels in the ponds do begin to show backwater effects on the pipes coming in from Garden Avenue North and the North Basin for the larger storms, as shown by the "plateau" of peak flows in these systems. 1 r r r , ' 910241 REPORTS/REGORAIN(1/27/93)/ahw 6 ' Table 1 Current Conditions of Houser Way North Drainage System ' Storm Recurrence Interval (years) 2 10 25 100 Design Flows Water level (ft) at PACCAR Outfall at North 8th St./Garden Ave. N 2.71 3.14 3.33 3.36 Pond 1 3.16 3.96 4.31 4.49 Flow (cfs) North 8th St. 76.9 82.7 82.9 82.9 39.7 - 79.7 Garden Ave. N (54-inch) 24.3 37.8 47.0 49.0 58.2 - 108.2 ' Garden Ave. N (72-inch) 87.9 149.9 146.8 155.4 72.8 - 351 .3 North Basin (pipe 401) 49.8 83.1 89.8 90.4 74.5 ' North Houser (pipe 430) 13.0 17.9 20.9 25.6 46.4 Pond system 204.4 276.7 316.7 343.9 174.6 - 1,709.4 Houser Open Channel 31.4 124.1 128.8 128.9 101.0 1. Theoretical design flows using Manning's equation. These assume open-channel flow and do not reflect surcharged conditions or downstream constraints. The ranges of flows reflect minimum and maximum designed for the different pipes in the system. ' The EXTRAN model also shows the amount of water which flows out of the system as flooding. Upsizing of the culverts in the pond system does not seem to change mod- eled street flooding relative to the preimproved model runs. The flooding at the Houser Way underpass is estimated at 0.1, 0.7, 1.4, and 2.5 acre-feet for the four design storms. No flooding is predicted along Garden Avenue North, where most of the re- gional stormwater flows to the pond system. However, the backwater conditions ' caused by the North 8th Street pipe do lead to a large amount of flooding at North 8th Street and Houser Way (1.1, 8.1, 13.9, and 22.7 acre-feet). Areas of predicted flooding are shown in figure 2. As noted before, one of the critical assumptions for this model- ing was that the overflow water from the area on the hillside is routed to the channel along Houser Way. It is primarily this flow which seems to result in the flooding in the ' vicinity of the intersection. Again, it is not certain how much of this flow is actually at- tenuated in the systems on the hillside. Any attenuation would probably lead to lower predicted flooding on the valley floor. tIn comparison, the 25-year storm for the existing conditions without the larger pond cul- verts (but with the assumption of maintained ponds) predicted 1.2 acre-feet of flooding ' at the underpass, 11.7 acre-feet at North 8th Street/Houser Way and 2.8 acre-feet on the hillside, although this run produced 10 percent less flow in the system than the im- proved condition run. The flow is less because this run used SWMM Runoff Block 910241 REPORTS/REGORAIN(313193)/jcw 7 ' modeling to determine the hydrographs, and this accounts for attenuation more than does the SBUH hydrographs. ' It is important to remember that flooding in this system is dictated both by high water levels downstream from the flooding areas and by high flow levels. Under the Houser Way underpass, the highest flow conveyed without flooding was predicted to be 82 cfs, which is approximately the peak flow of the 10-year storm. Likewise, the maximum predicted conveyance through the North 8th Street pipe is about 96 cfs before flooding, ' which is the flow predicted for the 10-year storm. However, with higher water levels at the outlet, these same flows would cause flooding, and less flow could be safely con- veyed. Because of the water level/flow interaction, it is difficult to establish flow levels above which flooding will occur for any one specific pipe section. ' EFFECT OF HOUSER WAY PROJECT ON STORMWATER SYSTEMS On a regional level, the effect of the Houser Way road improvement will be to alter an area along the railroad tracks south of North 8th Street, which currently serves as an open channel for storm flows. It is probable that, in order to construct the roadway, this ' channel will need to be replaced by an underground pipe. The drainage alternatives considered involve converting the channel to a pipe and providing some other im- provements to the system. Drainage Requirements ' The City of Renton drainage requirements are the same as those defined in the King County Surface Water Design Manual. For this study, Core Requirements 1-4 apply, as paraphrased and discussed below: 1. Runoff "must be discharged at the natural location". The intent of this requirement ' is to ensure that baseflows of streams are not changed by drainage changes, so the flow between pipes within a stormwater system is of lesser concern. Depending on interpretation, the natural location for discharge from this area could be consid- ered to be at a specific point within the stormwater system, at Pond 1 or at Lake Washington. Since the entire system from Houser Way to Pond 1 consists of piped storm drains, the natural discharge of this system reasonably can be assumed to be ' considered to be at Pond 1, which is the assumption used for this analysis. 2. Upstream and downstream areas which would be impacted by the changes to the ' drainage system must be analyzed. This study would presumably fulfill much of the analysis requirement. ' 91024/REPORTS/REGORAIN(1127193)1 ahw 8 ' 3. Restrict postproject peak flows to preproject levels. The regional analysis does not consider an increase in the amount of runoff generated in the project area, but this ' requirement applies in that the 100-year, 24-hour peak flow after improvement will be constrained to be no more than 0.5 cfs more than the pre-improved 100-year flow. Also, some regional biofiltration may be required as part of the Houser Way ' project to replace that occurring in the existing channel. 4. New pipe systems are to be designed to convey the 25-year peak flow. The pipes ' for this study were designed for such a rate, although, as mentioned earlier, those flows will have to be confirmed before final design. IMPROVEMENT ALTERNATIVES Description of Alternatives Three alternatives were considered to improve the functioning of the Houser Way drainage system. For this analysis, we assumed that: • Road placement will require filling the channel. • A 72-inch pipe will be necessary to convey the modeled flows. • Four 400-foot-long sections of 72-inch pipe will be set at the slope of the exist- ing ground surface. Alternative 1 is to replace the 42-inch pipe under North 8th Street with a 72-inch pipe. Alternative 2 is similar to this, but also involves removing the cross connection between the 54-inch and the 72-inch lines at North 8th Street and Garden Avenue North. Alternative 3 is to build a 10-foot wide swale and 48-inch overflow pipe along Houser Way North, north of North 8th Street, to divert some of the flows from the North 8th Street line and pick up drainage from the hillside. A conceptual drawing of this alter- native is shown in figure 4. The swale would have the same surface overflow rate as the existing channel for the 2-year flow, giving it comparable biofiltration capacity, as biofiltration is dominated by physical (settling) processes. The resulting predicted flows and water levels under each of these alternatives for the ' 100-year storm are shown in table 2. Replacement of the open channel with a 72-inch pipe is not expected to affect the ' drainage system compared to existing conditions. However, the existing flooding also continues, as well as the existing conveyance, so the replacement cannot be consid- ered to be a drainage improvement. ' 91024/REPORTS/REGORAW(1/27/93)/ahw 9 1 1 1 r I / V V \ 1 r � i r � � i J O 0o III •� d —7 1 l�s w ' I 111 1 111 � - r , " I HGU�5EK WAY N SWALE r6YPA59/G�EPFLO'JI PIPE i 1 r r HOUSER WAY NORTH REGIONAL DRAINAGE ANALYSIS . , ' E N T R A N C O Figure 4 0 Conceptual Drawing of North Houser Swale r 10 Table 2 Comparison of Houser Way North Alternatives ' 100-Year Storm Alternatives) ' 72-Inch Existing Pipe 1 2 3 Only ' Height at junction (ft) PACCAR Outfall at North 8th St./Garden Ave. N 3.36 3.36 7.07 5.51 3.39 Pond 1 4.49 4.50 5.03 5.15 4.68 Flow (cfs) North 8th St. 82.9 82.8 204.6 211.0 82.8 Garden Ave. N (54-inch) 49.0 47.5 73.3 63.4 66.5 Garden Ave. N (72-inch) 155.4 155.2 161.6 190.5 148.8 North Basin (pipe 401) 90.4 90.5 86.4 86.3 89.7 North Houser (pipe 430) 25.6 27.1 28.2 28.6 47.4 Pond System 343.9 342.9 411.4 424.8 366.4 Houser Channel 128.9 128.6 129.4 129.4 129.0 1. Alternative 1 is the North 8th Street upgrade. Alternative 2 is the North 8th Street upgrade with removal of the cross-connection at North 8th Street and Garden Avenue North. Alternative 3 is the bypass Swale. Alternative 1, increasing the size of the North 8th Street pipe, leads to increased con- veyance and reduced flooding throughout the system, eliminating the flooding at North 8th Street and Houser Way North with only a minimal (0.08 acre-foot) amount of flood- ing on Garden Avenue North. One major drawback for this option is that it leads to ' greatly increased water levels at the intersection of North 8th Street and Garden Avenue North (junction 1000), where drainage from the PACCAR site enters the sys- tem. The higher water levels could lead to restricting the flow of water off of that site and result in further flooding. In fact, the predicted flooding on the PACCAR site in- creases from 0.55 acre-foot to 2.0 acre-feet due to the enlarged pipe system. Alternative 2 improves on Alternative 1 by removing the cross-connection between the Garden Avenue North lines at North 8th Street. The result is increased conveyance through the two Garden Avenue North systems (a total of 254 cfs vs. 235 cfs, 204 cfs for existing) and down the North 8th Street line while the water level at the PACCAR outfall is 1.5 feet lower than in Alternative 1. This alternative does lead to some 910241 REPORTS/REGORAW(1/27193)1 ahw 11 ' flooding (0.5 acre-foot) from the North 8th Street line, and the water level at junction 1000 is still 2.15 feet higher than under the existing conditions. However, the predicted ' increase in flooding on the PACCAR site is only 0.15 acre-foot. Alternative 3, the bypass swale, like the first two alternatives, also reduces the pre- dicted flooding at North 8th Street and Houser Way North, although it does not elimi- nate that flooding. Additionally, it results in a slightly improved conveyance down Garden Avenue North, but does not affect the maximum flow down the North 8th Street line. Overall conveyance through the system is improved by about 23 cfs, and there is no effect on flooding on the PACCAR site. As mentioned above, the swale would re- produce the biofiltration from the existing channel, but there are some uncertainties re- garding this option, including the size of swale which can be built in the space available. This alternative could provide additional wetland functions which may be required as mitigation when the wetland is removed. ' These alternatives were run for the 25-year storm as well, and the results are shown in table 3. One of the more important results for the 25-year storm analysis is that i . Alternative 2 does not lead to increased flooding on the PACCAR site for this storm. It is possible that other drainage alternatives may achieve the same results, such as ' replacing one large pipe with two smaller ones, but these three alternatives were con- sidered the most viable. ' A concern about increasing the conveyance through the system is that increases in peak flows will lead to a requirement to provide detention. It is unknown whether the area exists to provide the detention for these alternatives, which would increase the peak flows through the pond system by as much as 82 cfs. The cost for such a facility in this area could be expected to be significant. ' Of the three alternatives evaluated to improve drainage in the vicinity of Houser Way, Alternative 2 appears to be superior to Alternative 1, as the removal of a cross ' connection seems to improve drainage in the Garden Avenue North lines. Alternative 3 does not reduce flooding as much as the other two, but it provides biofiltration and does not affect the drainage off of the PACCAR site. Cost of Alternatives A planning level cost analysis was conducted for the three alternatives. The costs for Alternatives 1 and 2 were the same ($1,996,000), as the cost of removing the cross ' connection was assumed to be negligible. Alternative 3 would cost $2,824,000. These are planning level costs, and are subject to change before final design. The calcula- tions for these costs are shown in Attachment A-1. 1 ' 91024/REPORTS/REGD"N(313/93)/jcw 12 tTable 3 Comparison of Houser Way North Alternatives ' 25-Year Storm Alternatives) ' 72-Inc h Existing Pipe 1 2 3 Only Height at junction (ft) PACCAR Outfall at North 8th St./Garden Ave. N 3.33 3.34 6.95 5.08 3.20 Pond 1 4.31 4.30 4.89 4.98 4.44 ' Flow (cfs) North 8th St. 82.9 82.9 209.0 203.2 82.7 ' Garden Ave. N (54-inch) 47.0 48.9 73.5 62.0 42.0 Garden Ave. N (72-inch) 146.8 149.1 169.1 188.9 153.8 North Basin (pipe 401) 89.8 90.0 86.0 85.9 89.4 ' North Houser (pipe 430) 20.9 20.9 21.1 21.3 39.6 Pond System 316.7 321.3 391.9 402.2 335.9 ' Houser Channel 128.8 117.1 117.1 117.1 117.1 Flooding (acre-ft)2 Houser & North 8th St. 13.9 15.6 0.0 0.0 5.4 North Houser 1.4 1.5 1.5 1.5 2.3 PACCAR Site 0.3 0.3 0.5 0.3 0.3 1. Alternative 1 is the North 8th Street upgrade. Alternative 2 is the North 8th Street upgrade with removal of the cross-connection at North 8th Street and Garden Avenue. Alternative 3 is the bypass ' Swale. 2. See figure 2 for locations. Cost Reduction Options ' Entranco also investigated conceptually various options to reduce the high costs of these alternatives while providing equivalent drainage functions. It is important to note that most of the predicted peak flow in the planned 72-inch Houser Way North pipe is due to the overflow from the eastern basin. Without this ' overflow, the peak flow through the channel would be reduced by more than 60 per- cent-a 42-inch pipe may be sufficient to convey the flows. The eastern overflow could ' 91024/REPORTS/REGORAIN(1/27193)/ahw 13 ' be reduced by installing a regional detention facility on the hillside. It is estimated that using a 42-inch pipe along Houser Way would save about $440,000. A second cost-saving option would be to use two smaller pipes instead of one large pipe to improve the system. Using a 42-inch and a 48-inch pipe along Houser Way ' North would save $115,000 in material and excavation costs, and installing a 48-inch pipe parallel to the existing system along North 8th Street would save $310,000 over replacement with a 72-inch pipe. ' It appears that the most economical measure would be to develop a regional detention facility, as it may be eligible for cost-sharing with other agencies. This would allow ' downsizing of conveyance facilities through the project while possibly reducing the flows and flooding in the valley area. ' RECOMMENDATIONS FOR FURTHER STUDY ' There are at least two drainage issues regarding the Houser Way Improvement project which will be important to clarify when proceeding with that project. The first is the pre- viously mentioned drainage/overflow off of the hillside, and the resulting flooding on the valley floor, the amount of which must be verified before final desiqn. The second issue is that a portion of the project area currently drains to a bypass pipe which runs through the PACCAR site. Since the flow through the bypass is limited, peak runoff flow rates ' may be restricted and additional detention may be required in that part of the site. ' REFERENCES Entranco ' 1991 Garden Avenue Drainage Study. Prepared for PACCAR, Inc. October 1, 1991. ' City of Renton 1988 North Renton Basin. Interim Drainage Study to Address Development West ' of 1-405. May 1988. 91024/REPORTS/REGORAIN(1/27193)/ahw 14 ' Attachment A-1 ' PLANNING LEVEL COST ESTIMATE t t 1 1 1 . . 1 SHEET NO. / OF Z ENTRANCO ENGINEERS, INC. JOB NO. PROJECT CALCULATIONS FOR �- MADE BY T DATE 4 / ? /g z CHECKED BY DATE -- 1 , po Di vc-nstv.�wT%4c/z- V/+tJG7 coo - -- 10 HOIZI _ -C-0v p =i 051 ". . s urn -ToT, . !Z /a N 13 l 0 i A L--:--- � ' Q SHEET NO. OF Z �+ ENTRANCO ENGINEERS,•INC. JOB NO. 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C I 14, 5-2 - 12.C5-9 tG5- _E5- w D5- 2.05-1 12.C5-i 12 5-3 12, j I - 12C5-2 12,06-1 It.06-2 \ . \ 12.F5-I 1 2D6-I - \ / 12.D8-10 12.06- \ NR - 17 ' 12.D8-9 I I 12.DB-B 1;. 12.06-3 f 12 D6-7 l I Q------'- -)11.08-13 12.08-6 7` 12.06-I5 12 D6-i 12.D6-16 1 6-1 12.fB-1 12.D7-1 /^\ 12.07-1 1 12.F6-4 12.07- 12.P7-2 � - 18 12.U7-. ,VR - 22 ,t :7-5 12.C7-1 12.C7-6 NR - 26 - 12.D7-I } 7-� 12.D7-2 1 L, 12.D7-'11 1 12.F7-4 --- 0r 2 3 E 1 i � w i 12.F7-) P 12.D6-I S R GB- N - 0 NR - 29 i 12.ce- 1 .fe-i .-----ty�------- 12,oe-z 12,C8-I 2.C8-3 � � � � � � r � � � � � � � � � 1 ' Drainage Analysis 9 Y HOUSER WAY RELOCATION PROJECT ' Stage II Study Prepared for ' City of Renton Prepared by ' ENTRANCO 10900 NE 8th Street, Suite 300 Bellevue, Washington 98004 ' (206) 454-5600 ' August 19, 1993 1 1 1 1 i 1 1 1 rDrainage Analysis HOUSER WAY RELOCATION PROJECT Stage 11 Study ' Prepared for ' City of Renton ' Prepared by ENTRANCO 10900 NE 8th Street, Suite 300 Bellevue, Washington 98004 ' (206) 454-5600 August 19, 1993 1 r ' HOUSER WAY REGIONAL DRAINAGE t INTRODUCTION This report is a summary of continued hydrologic/hydraulic analyses associated with the ' proposed Houser Way North Relocation Project. The roadway improvement involves relocating a previously vacated section of Houser Way North and resurfacing sections of existing roadway. The project limits extend from the Houser Way/Lake Washington ' Boulevard intersection south to the Houser Way/Sunset Boulevard intersection. From Lake Washington Boulevard south to North 8th Street, the project will involve resurfacing existing roadway. From North 8th Street south to Sunset Boulevard, the project will ' involve constructing a new roadway that follows an alignment along the western boundary of the 1-405 corridor. ' Existing drainage patterns will be affected by increased stormwater runoff volumes (as a result of the new construction), and containment and transport of regional drainage which currently passes through the corridor. The impacts and mitigation of increased ' runoff as a result of the resurfacing north of North 8th Street will be addressed in later analyses as a part of the on-site drainage design. This report addresses only the issues associated with changes in the regional drainage system affected by the relocated ' portion of the roadway (between North 8th Street and Sunset Boulevard). These solutions are shown on figure 1. Within this area, an open drainage swale that currently conveys local and regional drainage will be replaced by a regional drainage pipe. Other reports addressing the regional drainage as it affects the Houser Way North ' project have been prepared by Entranco. The initial assessment of regional drainage issues was presented in the Houser Way North Regional Drainage Analysis dated January, 1993, and is an Appendix to this memo. Streamflow monitoring in the vicinity of the project was conducted during the winter of 1992-93 with the results summarized in a technical memorandum dated June 4, 1993 (Entranco 1993). ' This report incorporates these earlier findings and provides an updated assessment of regional drainage conditions and solutions as they pertain to the Houser Way North Relocation Project. PROJECT BACKGROUND The proposed Houser Way relocation is located in what is referred to as the North Renton Drainage basin. The basin encompasses approximately 1,230 acres, comprised ' of mixed residential and commercial land uses, draining north and west to Johns Creek at Gene Coulon Memorial Beach Park before discharging into Lake Washington. 930101 Tochmemo/Storm(9/10/93)/jnw 1 .;: ilk Gene u Co Ion ri.';<:;i::;:;is»::>:::>:x:::;:;::.>::>;>[::«:: Memorial Beach Park >. ....:::::: ::»::>::::>::::::>::<:>::>:«::<:>:.EGEND m a Existing Pipe System y a Pon d System to m NE 12h St /. Overflow route ....••• a 900 �•• 54-inch pipe for � �... 900 Qom' •• O Al 'v 1 and 2 Q,. m s Alt alle ♦ Alternative 3 42-inch pipe for AI to Alternative '•. aos Alternative Z :. p 1/8 1I4 2 ��ai'Z 3 m m MILE goo N Y1� CD � m • L � f a ¢' N 8th St ..• Y ,• ro a i Alternative Existing Swale/ Proposed = 1 ' Regional Drainage Pipe * =1 N 5th St z ' < c v N 4th St C7 m a o _a N C � ❑� JC a0s m Q ' a HOU ;ER WAY NORTH REGIONAL DRAINAGE Figure 1 ® E N T R A N C O Regional Drainage Alternatives ' The hydrology of the basin and the hydraulics of the storm drain system on the valley floor have been the subject of previous reports completed by Entranco. Drainage analyses completed in support of the Park Avenue Improvements delineated the overall ' basin and predicted flows for various return frequencies using the SSUH methodology (Entranco 1992). Work conducted as a part of the Garden Avenue storm drain improvements for the PACCAR development resulted in the detailed hydraulic modeling of the principal storm drain system on the valley floor (Entranco 1991). Preliminary studies for the Houser Way relocation project focused on the hydrology and hydraulics for the area in the immediate vicinity of the roadway relocation (Entranco 1993 and Appendix). ' The proposed Houser Way project involves replacing a linear wetland/swale with a storm drain in order to allow the roadway to be constructed. This swale conveys runoff from approximately 124 acres east of 1-405. In addition, at times of extreme runoff, the swale ' can carry overflow from additional tributary areas that are served by undersized storm drains. The overflow condition may begin to occur at a frequency of approximately once every ten years (the level of the ten-year design storm). The predicted occurrence of the overflow was questioned by Entranco in earlier analyses. During the winter of 1992-93, stormflow monitoring was conducted to verify ' predicted flow magnitudes and determine if an overflow does occur. In general, it was concluded that the assumptions and parameters used to predict flows in the North Renton basin appear to be reasonable with respect to observed flows (Entranco 1993). However, storms of a magnitude comparable to the design storms were not encountered during the monitoring period. Overflow conditions for the existing storm drain system were not observed. In the absence of any data to the contrary, it is concluded that the overflow condition will need to be accommodated by the regional drainage system for Houser Way North. Review and evaluation of the storm drain system in the area east of 1-405 indicates that much of the principal storm drain system is, in fact, undersized with respect to the design storms. In the event of a severe storm, overflows would occur throughout the upland ' area. Due to the general slope of the land, it is believed that excess water would flow along the surface of the streets in a general south and west pattern. Eventually, the excess water would cross 1-405 and enter the Houser Way corridor. The size of pipe needed to convey regional drainage through the proposed Houser Way North roadway corridor would be controlled by the amount of flow entering along the southern project limits, as well as the amount of flow that can be discharged into the North 8th Street storm drain. The predicted 25-year flow rate for the regional drainage passing through the existing swale is 122 cfs. The existing drainage system along North 8th Street (between Houser Way North and Garden Avenue North) consists primarily of a 42-inch-diameter pipe laid on a relatively flat slope. The full-flow capacity of the North 8th Street system is 83 cfs. The undersized storm drain creates high water levels, 930101 Techmemo/Storm(9/10193)1 jcw 3 thereby limiting the outlet capacity from the swale. During flood events, it is likely that excess stormwater can backup into and be stored in the swale. ' REGIONAL DRAINAGE ALTERNATIVES Alternatives to address regional drainage can be broken down into three general categories, each of which have been addressed to some degree in previous submittals. The general categories are: increasing the capacity of the storm drain along North 8th Street, diverting stormwater northward along Houser Way North, and diverting water in the upper watershed to the northern part of the project in an attempt to lessen the ' magnitude of flows entering the Houser Way project corridor. An update as to the feasibility of these options is described below. ' Alternative 1 : Increase the capacity of the North 8th Street Storm Drain ' Description. Increase the flow capacity along North 8th Street, thereby reducing flooding and lowering water levels in the vicinity of Houser Way North. The best way to do this appears to be by adding a 54-inch-diameter storm drain to convey regional and ' on-site Houser Way North flows to the Garden Avenue North storm drain. The existing 42-inch storm drain along North 8th Street (between Houser Way North and Garden Avenue North) would remain in place. Runoff conveyed by the two storm drains along North 8th Street would not be combined until it reached Garden Avenue North. ' The 54-inch-diameter storm drain would be sized to accommodate regional flows and estimated flows from the new roadway. However, the size of storm drain required will not be confirmed until the on-site drainage analyses are completed. The ability to increase the capacity of the North 8th Street line may be limited by the PACCAR outfall at North 8th Street and Garden Avenue North. The recently-constructed 72-inch storm drain along Garden Avenue is connected to the PACCAR outfall. Critical water levels occur if the discharge capacity from the PACCAR site is reduced by high water levels in the Garden Avenue North pipes or, in the extreme case, if water levels ' exceed the ground surface elevation on the site. According to available record drawings, it appears that the lowest grate elevation on the storm drain is 25.6 feet. The cross-connection between the two storm drains on Garden Avenue North (the 72- inch line and the 54-inch line) will need to be moved from its existing location farther downstream in order to minimize the potential for increasing water levels at the PACCAR 1 outfall. Preliminary Planning Level Cost. $980,000 93010/Techmemo/Storm(9/10/93)/icw 4 rAdvantages. Flooding in the vicinity of North 8th Street and Houser Way North would be substantially reduced for the 25-year storm event. Street flooding is predicted to be ' reduced from 9.8 to 1.7 acre-feet of water. The effect of this flooding on adjacent properties is undetermined at this time. ' Disadvantages. Water levels at the PACCAR outfall would be increased to the greatest extent of all alternatives examined. The increase is sufficient to cause approximately 0.7 acre-foot of flooding on the PACCAR site. Potential damages caused by this flooding ' are undetermined. The benefits of reduced street flooding at North 8th Street and Houser Way North could offset the PACCAR flooding, if the current street flooding at North 8th Street and Houser Way North ultimately flows to the PACCAR property. ' However, the expected behavior of flood waters at North 8th Street and Houser Way North has not been determined. ' Peak flows in the vicinity of Gene Coulon Memorial Beach Park increase from 295 to 384 cfs. The increase in flows is attributed to a reduction of flood storage along Houser Way North and the reduction of street flooding at North 8th Street and Houser Way North. The increase in flow would have to be mitigated per the King County Surface Water Design Manual requirements. At the present time, detention required for replacing lost flood storage in the existing Swale is assumed to be incorporated with the on-site detention, and will be addressed as a part of the roadway drainage analyses. Predicted velocities in the open channel section would increase from 4.1 to 4.5 feet per seconds (fps). These velocities are below the maximum permissible velocity of 5.0 fps for vegetated channels recommended in the King County Surface Water Design Manual. ' Comments. Portions of this alternative could be viewed as a regional solution; therefore, funding by the City of Renton Stormwater Utility may be justified on the basis of the elimination or reduction of flooding at the intersection of North 8th Street and ' Houser Way North. ' Alternative 2: Divert flows northward along Houser Way North Description. Convey regional and on-site drainage from the Houser Way North corridor ' (south of North 8th Street) northward to Gene Coulon Memorial Beach Park using an alignment following Houser Way North. In previous analyses, this alternative assumed ' an open swale would be constructed to replace some of the lost functions (habitat/water quality treatment) currently provided by the existing swale south of North 8th Street. However, at the present time it is assumed that mitigation will be accomplished within the new roadway corridor, and additional mitigation will not be required. As a result, the proposed alternative is assumed to consist of a single, 54-inch pipe running approximately 2,700 feet along Houser Way North, between North 8th Street and Gene Coulon Memorial Beach Park. t93010/Techmemo/Storm(9110/93)1 jcw 5 ' The diversion pipe is sized to convey only the regional and on-site flows from the new Houser Way North roadway. No additional flows would enter the system north of North ' 8th Street. No other improvements to the North 8th Street system (joining Garden Avenue North) ' would be made at this time. Preliminary Planning Level Cost. $1,600,000 tAdvantages. As in Alternative 1, flooding in the vicinity of North 8th Street and Houser Way North would be reduced for the 25-year storm event. Street flooding is predicted to ' be lowered from 9.8 to 1.7 acre-feet of water. The effect of this flooding on adjacent properties is undetermined at this time. Flow would be diverted away from the Garden Avenue storm drain, minimizing impacts to ' the PACCAR outfall. However, reducing flooding at North 8th Street and Houser Way North would cause higher water levels in the pond system and subsequently at the ' PACCAR outfall. This alternative could, as previously described, incorporate an open swale, thus providing an additional option for mitigation should on-site mitigation prove to be unfeasible. ' Disadvantages. As mentioned above, the water level at the PACCAR outfall (at North 8th Street and Garden Avenue North) is predicted to increase slightly due to higher water levels in the lower pond system. As a result. 0.3 acre-foot of flooding on the PACCAR site is predicted for the 25-year storm. This amount is less than that caused by Alternative 1 (0.7 acre-foot). ' The peak flows for the 25-year storm in the open channel of Gene Coulon Memorial Beach Park are predicted to increase from 295 to 406 cfs, a higher increase than that predicted for Alternative 1. As described under Alternative 1, this increase in flow would ' have to be mitigated per the King County Surface Water Design Manual requirements. At the present time, it is assumed that mitigation for the regional flow increases will be integrated with the on-site mitigation, which will be designed at a later date. ' Maximum velocities are predicted to increase from 4.1 to 4.6 fps. These velocities are below the maximum permissible velocity of 5.0 fps for vegetated channels recommended ' in the King County Surface Water Design Manual. Comments. Portions of this alternative could be viewed as a regional solution; ' therefore, funding by the City of Renton Stormwater Utility may be justified, on the basis of the elimination or reduction of flooding at the intersection of North 8th Street and ' Houser Way North. ' 930101 Techmemo/Storm(9/1M3)/irw 6 ' This alternative is sized to accommodate only flows from the Houser Way regional drainage pipe conveyance line (south of North 8th Street) which directly affect Houser ' Way North. It is possible to increase the pipe size to pick up additional drainage north of North 8th Street. Increased flow capacity could be accommodated by participation by the City of Renton Stormwater Utility. ' away Alternative 3: Divert upland flows from North 8th Street t p y ' and Houser Way North Description. Divert flows in upland tributary areas (east of 1-405) away from the ' intersection of North 8th Street and Houser Way North to a wooded ravine opening up to the eastern side of 1-405. At this site, construct a regional stormwater facility designed to provide detention and water quality treatment. Flows leaving the facility would be ' conveyed across 1-405, then directed north along Houser Way North before entering the pond system at Gene Coulon Memorial Beach Park. ' Preliminary Planning Level Cost. Planning level cost has not been determined at this time, due to uncertainties associated with the type of regional facility and the extent of improvements required to effectively divert water in the upland areas. ' Advantages. This alternative allows opportunity for regional detention and water quality improvements. As part of this alternative, existing problems would be remedied, such as erosion in the open channel above 1-405, and damage in the pipe passing beneath 1-405, which is evidenced by flows exiting the pipe bedding on the downstream side. ' By diverting flows away from the Houser Way North project, the regional drainage pipe required for passing regional flows along the relocated Houser Way North would be reduced from a 54-inch pipe to a 42-inch pipe. No other improvements along North 8th Street to Garden Avenue would be required, provided that enough flows could be diverted in the upland areas. This alternative has regional benefits, thereby justifying participation by the City of Renton Stormwater Utility. It is also possible that Centennial Grant funds from the Washington State Department of Ecology could be used for design and construction, ' provided it is addressed by the Step 1 water quality study currently being conducted by the City. ' Disadvantages. The extent of drainage system upgrades that would be required in upland areas is undetermined at this time. It appears that much of the existing system is undersized for the design storms. As a result, extensive improvements could be required ' in order to reliably divert runoff to the new facility. If street flooding were allowed to continue, runoff would be directed by the surface topography which slopes to the south ' and west, away from the proposed facility, for much of the upland area. 93010/Techmemo/Storm(9/10193)/jcw 7 Constructing a new facility adjacent to 1-405 would require extensive coordination between various agencies, such as WSDOT, Puget Power, and private landowners. The time required for coordination could delay the construction of the improvements, thereby ' delaying the completion of the roadway project. Comments. This alternative is not being actively pursued at the present time due to ' uncertainty associated with coordinating with other parties. It is uncertain whether or not the facility could be built, the type of facility that could be constructed, and the timing of ' construction. REFERENCES ' Entranco ' 1991 Garden Avenue Drainage Study. 1992 Final Design Studies. Park Avenue Improvements Project. 1993 North Renton Monitoring Plan. Technical Memorandum. June 4, 1993. 1 r ' 93010/Techmemo/Storm(9/10/93)/jcw 8 ' APPENDIX Regional Drainage Analysis ' January 1993