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05-210 (20060545) Michel Storm 062106.pdfGARY HAAKENSON CITY OF EDMONDSMAYOR 121 5TH AVENUE NORTH • EDMONDS, WA 98020 • (425) 771-0220 • FAX (425) 771-0221 Website: wwwdedmondsma.us DEVELOPMENT SERVICES DEPARTMENT Planning • Building • Engineering June 21, 2006 Donna L. Breske, P.E. 6621 Foster Slough Road Snohomish, WA 98290 RE: Michel Single Family Residence — 1591174th Place West Dear Ms. Breske: This letter is in response to your letter dated August 8, 2005, which is attached for your reference. You are correct in your interpretation of the Edmonds Community Development Code that meadows or young second growth forest are allowed to be assumed for the predeveloped site condition. However, in an instance where the existing lot is wooded prior to development, the assumption of meadows as the predeveloped site condition is unacceptable. In this case, the existing site condition prior to development is clearly more accurately represented by young second growth forest than by meadows; therefore, a storm drainage report using meadows as the predeveloped site condition will not be approved. Please revise and resubmit the storm drainage detention report dated May 19, 2005 accordingly. Also, please note that, per ECDC 18.30.010, the two-year, 24-hour design storm in the City of Edmonds is defined as a 1.5 -inch rainfall event. Please revise the time of concentration calculations for the predeveloped site condition to reflect this. If you have any questions or need additional information, please email me at droth ei.edmonds.wa.us or give me a call at (425) 771-0220. DAMON K. ROTH Stormwater Engineer DKR/cmc Enclosure S:\ENGR\Damon\Development Reviews\LETTER-Bieske-15911-74th-PI doc • Incorporated August 11, 1890 • Sister City - Hekinan, Japan DONNA L. BRESKE, P.E. 6621 Foster Slough Rd. Ph: 425-334-9980 Snohomish, WA 98290 Fax: 425-334-7380 STORM DRAINAGE DETENTION REPORT MICHEL CONSTRUCTION, INC. SINGLE FAMRX L( )T .DATA. May 1.9,2005 sal:41: 74,11"1 P.f W". EDMONDS, WA 98026 ev V4 0 L/ A 273;67 ExPRES::�� [)FIVU F '' N'O DRAINAGE -DETEN'BON INSPECTION -GRADING &TESC SEWER& WATER --FEASIBILITY SITEDEVELOPME LAI M'$ . `1 MICHEL CONSTRUCTION, INC. 74"" PL. W. SINGLE FAMILY HOME OVERVIEW: A single family home is proposed for construction on the subject lot. Currently the property is covered with vegetation with no structures on site. The site slopes downward from east to west with maximum slopes of approximately 45%. A total impervious area, (rooftop and driving surface) used for calculating the detention system i ,37 sf. I?3 d� DESIGN: U Sf . The site area is 0.61. The site is less than one acre in size and is located in close proximity to Puget Sound. The storm water detention system is therefore designed in accordance with the SBUH method and the ECDC 18.30.060.A. Lc for the 10 and 100 - year 24-hour storm events. The release structure is designed to release flows for the two storms events matching the 10 and 100 pre -developed peak flows.. A chart of the pre - developed and post -developed flows is shown below: DESCRIPTION 10 -YR, 24 -HR 100 -YR, 24 -HR .......... PRE -DEVELOPED DEVELOPED FLOWS 06 cfs .14 cfs FLOWS 12 cfs .24 cfs CONTROLLED RELEASE DEV FLOWS .06 cfs .14 cfs DRAINAGE — DETENTION — INSPECTION — GRADING & TESC SEWER & WATER — FEASIBILITY — SITE DEVELOPMENT I N I M i'chc ( 6pr6fruc�c V) I lea i► I I Pl tcrI5 Es P2 P2,00 Cj C, 10 C�A P(OO E�(6T/Na (Cf -IN = =(95- Z Pervt*c)us: DEVELOPED C_O9VMOiy,., Iryipelf , 10 US". Rooftop k Road Trees 5 a30© 17 000 5F CR A3 7q 5F �N Avg 1_ 3 I 0� 77 2 Per �CDC [9,3o,obo,4,1.c_ rKev'rillzu'l the Predetle-lefeel Ccnd,�4orl pectkruylog rcc�e -I r th-e to -year 4 /00- de5(,Fyj sforin5. 5/19/05 page 1 Michel Construction, 74th, North Lot BASIN SUMMARY BASIN ID: A10OX SBUH METHODOLOGY TOTAL AREA.......: RAINFALL TYPE....: PRECIPITATION....: TIME INTERVAL....: TIME OF CONC.....: ABSTRACTION COEFF: NAME: 100 YR 24 HR EXISTING 0.61 Acres TYPEIA 3.00 inches 10.00 min 39.75 min 0.20 PEAK RATE: 0.14 cfs VOL: 0.08 BASEFLOWS: 0.00 cfs PERVIOUS AREA,,-,.,,_ AREA..:°��,»Acres TYPEIA CN....: 5 0_ ... AR,:'.: 0.00 Acres .,.: 98.00 Ac ft TIME: 490 min 6.30 min IMPERVIOUS X-22E:A-a BASIN ID: A10X NAME: 10 YR �4 HR EXISTING SBUH METHODOLOGY TOTAL AREA.......: 0.61 Acres BFLOWS: 0.00 cfs RAINFALL TYPE....: TYPEIA PERVIOUS AREA PRECIPITATIONTIME INTERVAL....: 10.00 min CN .... �, 85. 0 res ... 2.00 inches AREA. ..:. Ac TIME OF CONC..... • 39.75 min IMPERVIOUS ABSTRACTION COEFF: 0.20 AREA..: 0.00 Acres CN....:. 98.00 TcReach - Sheet L: 95.00 ns:0.4000 p2yr: 1.30 s:0.4600 TcReach - Sheet L: 110.00 ns:0.4000 p2yr: 1.30 s:0.0540 TcReach - Sheet L: 50.00 ns:0.4000 p2yr: 1.30 s:0.3600 PEAK RATE: 0.06 cfs VOL: 0.04 Ac -ft TIME: 490 min BASIN ID: B100D SBUH METHODOLOGY TOTAL AREA........ RAINFALL TYPE....: PRECIPITATION....: TIME INTERVAL....: TIME OF CONC.....: ABSTRACTION COEFF: NAME: 100 YR 24 HR DEVELOPED 0.61 Acres BASEFLOWS : ...�7, cfs TYPEIA PERVIOUS AEA 3.00 inches AREA..: 0.42 tes 10.00 min CN..... 82.00 6.30 min IMPERVIOUS X-22E:A-a 0.20 AREA..: PEAK RATE: 0.24 cfs VOL: CN..... 0.09 Ac -ft TIME: 0.19 Acres 98.00 480 min 2,3q, 103,1 �,S- + H-1 -:- zi, 4 c � E I q,U'Ua1e,0'-- lerj+A oF ZS - (1.2s)2 x L= 2—+.4 L = 51 Hence use 75- L -F of zsl 5/19/05 Michel Construction, page 74th, North Lot STORAGE STRUCTURE LIST UNDERGROUND PIPE ID No. Pi Description: DETENTION PIPE Diameter: 2.50 ft. Length: 80.00 ft. Slope...: 0.0000 ft/ft Oe -crease in pj,pe le mn FV a hd a Tjfpe Cg 2,3q, 103,1 �,S- + H-1 -:- zi, 4 c � E I q,U'Ua1e,0'-- lerj+A oF ZS - (1.2s)2 x L= 2—+.4 L = 51 Hence use 75- L -F of zsl