The URL can be used to link to this page

Home My WebLink AboutDrainage Reports - 07/09/2014May 9, 2014 Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80522 INCORPORATED City of Ft. Collin pr ed Plans Approved By Date — —1 Subject: Drainage Review for Redevelopment of 316 Willow Street Fort Collins, Colorado CTLIT Project Number: FC06217-145 Dear Mr. Lamarque, This letter summarizes the current and proposed lot drainage conditions relating to the proposed redevelopment of this 5286 SF commercial lot.. Current Conditions: The lot is located on the northeast side of Willow Street in the Old Town area of Fort Collins. An existing 1200 SF +/- single story masonry structure currently occupies the site. A gravel parking lot covers a majority of the site, while small stretches of grass are located along the rear of the building. The site is quite flat. In addition to the property, additional runoff comes from the offsite gravel area between the property line and the pavement for Willow Street. Half of the paved portion of Willow Street, between the extended property lines, was also included in our runoff calculations. The two offsite areas add approximately 2659 SF of design drainage to the calculated runoff. The runoff from the roof currently flows off the rear of the building to the northeast property line, and continues in that direction across the backyards of 405 and 409 Linden Street, both of which are currently lots with single family dwellings. After crossing those 2 lots, drainage continues on to Poudre Street, which slopes southeast to Linden Street. Due to the surrounding grade, it appears that the water which gathers on the existing front gravel area (and offsite areas) either percolates into the soil or also flows off site to the northeast. Proposed Conditions: The proposed redevelopment will slightly increase the amount of roof area, but will also increase the amount of turf and landscape area. No onsite parking is planned. As a result, the effective runoff coefficient for the contributing area will decrease from approximately 0.62 to 0.57. Refer to the table below for calculations. 351 Linden Street i Suite 140 i Fort Collins, Colorado 80524 Telephone:970-206-9455 Fax:970-206-9441 Existing Condition Item Ce Area (sq Product Roof 0.95 1403 1332.85 Pavement 0.95 761 722.95 Compacted Gravel 0.5 5771 2885.5 Subtotal 7935 ' 4941.3 Average Coefficient 0.62 Proposed Condition Item Ce Areas Product Roof 0.95 1764 1675.8 Walk / Patio 0.95 285 270.75 Compacted Gravel 0.5 2729 1364.5 Pavement 0.95 761 722.95 Grass 0.2 2396 479.2 Subtotal 7935 4513.2 Average Coefficient 0.57 Because the overall runoff from the site is reduced as a result of development, we have not designed for onsite storage. However, a bio-retention (rain garden) system has been designed to treat the water as it flows off site or percolates down through the soil below. Due to the site topography and subsurface conditions, any water that does not overflow the rain garden will percolate into the existing subsurface soils. _ CTLIThompson did perform percolation tests that indicated an infiltration rate of 0.50 inches per hour in the location of the proposed rain garden. Using a safety factor of 2, that percolation rate would reduce to 0.25 inches per hour. In large storm events, water will overtop the rain garden and flow to the northeast through a swale along the northwest boundary of the property and continue towards Poudre Street. Future improvements to Willow Street will likely create curb and gutter and storm drains, which are expected to further reduce the runoff from offsite. Water Quality Capture Volume: Based on the combined onsite and offsite area of 7945 SF, the calculated water quality capture volume for the rain garden is 121 cubic feet. The proposed rain garden on this site, per the site plan 1-1.1, will have a storage volume of 183 cubic feet. Therefore, we will be collecting 50% more than the required volume. That collected volume, as indicated earlier, will all percolate into the soil below and represents the equivalent of % inch of rain over the entire drainage area. Thank you for time in reviewing this submittal. Please contact our office if you have any questions. 2 WOLVERINE FARM PUBLISHING 316 WILLOW STREET, FORT COLLINS CTL I T PROJECT NO. FC06217-146 Very truly yours RED CTLITHOMp' 'i NC. • '!S� 35177 Wayne Thonion, E, LEEQ_A Project Mana @Of •' , J 9 tiSinnlnl E Attachments: Google Earth Aerial View Site Plan Water Quality Capture Volume Calculations WOLVERINE FARM PUBLISHING 316 WILLOW STREET, FORT COLLINS CTL I T PROJECT NO. FC06217-146 9 Google earth feet 300 meters-90 boa LAND USE INFORMATION E.IeTMa ZOWM RM EMSTI GM 'fO " Ma.a UVEL 'e'_ " S`ffl, aInSTEY a TRaouPEo NELYW 91eQIXa MEA1rT OIaMQblvq sT/JlallovMING oalMl IMK XAMQICNM10iiG Ilplwry SERNCE r I In00Ft ESLWIEQ FINII MFA HAUL MIIp II%IalIEiMY•p1. b�� r4•P ME apn lug 1a M 4bwl TaYI iU1LMaFOp1MiM 12130 90b N• vuwaaolM1Fa aw lcr os caNi lWl1{S MCMW Also aabw 1% rEW PaOrMN}.Fa are ool aaw as UVC8r1.PE raniwb Mta 02., 16% INCBGIE N Vk eaw 05. ws Tw.$MF 6A Siase ot:.tuw 1,0% IMPERVIOUS SURFACE CALCULATION FiYae Iwo scui,� Do euux dnw santPnaus raw BErL M]I'M1; alw b®6a 1 V fK MriD eiER11a16 INa.a PROPOSED USE INFORMATION Yepl v4w:e ba.M.. prig w.v. wn.EnnwE.P err r amaPra .erp..aaawrimrar. W^•�yr a,...arvw m we. wye,ry an. ap wwr. •nt+a e.. rb Iw •mavtl nM1vsald PeOe^�nFep,y rwUnp• w.wp, ma. bwYW ,wNgr. M. W v<wrN •vw M W bp�tl[erpn..b w�we WrMbbQc•b wrwahW sPwfor n+MR acri •Ande W./•M lnw••mlldlin lay NfP Yon u rwll •a • vrar rnrhrrcu rtem4 vnrx cobMP .np �weYa• Opxr Sww w bn� M bw...n.rimm.n u., y,e.n.r, Yry wwr pre. W r a.ww. ra zm+e whoa. s.a:nslw a wn.r NsrYow bMcgay=�n^•^y'+•e ww+wmvmm o®bW orL-a, ,,YhYa. Y✓vY n•dT. mti[. •rq MmNtluutYi YYM1y n/bulnWn On ev pefin Mlw.a Y1bCepAp awu•Mp•wlfor Nn Pgeainn W MpeNY eumw rab9 b wpwY Ira ew• •ma.Iuya. rr Y u. dry pwipars,tl�SwrnT. womW xov YCbnYv, sw.r Ian. apn wwr cuwa TueWy yn. pp,n WPw4•r a.n. sign rw.rr a.n . Itpn rwr a. ei. nn erw.v pen. Pn Setback 15' — Roised Pla ter Bed Sae Temp. Asphalt Walk Low Stone Boulder 4• Top Above Grade Entra a Gale See z Concrete Path, Providing Handicap Route. See ® - Stone Inlay Wolverine Farm Sign With Lighting Inside Raised Planter Bed — Dry Stack Stone Wall - Bike Rocks (30 Bikes) Compacted Gravel — Large Stone Boulders, Typical. Slone Curb 40• Fence Low Slone Boulder 4• Top Above Grade I a4 a el I e'te9 I I I I I I I I I I I I I I II - Rain Gorden, See - Low Voltage Down -Facing Landscape Lighting Typ. - Concrete Pad 10' x 10.5' Bike Storage (6 Bikes) 2 8 0 4' 16' urban I rural I design 2151e8erson street fort collins, wicrado 970.84E 0267 bnan@urdesignarch cam structure! engineer qr CTLITNOMP8ON CTL I Thompson, Inc 351 linden street, nude 140 fort coons, co 80524 970.208.9458 landscape architect: didierdesignstudio cider design studio tic 342 west douglas road fort cdlins, co 80524 970.418 1018 Site Plan 2000.01 02 May. 2014 VW ED L1.1 g Designer: Company: Date: Project: Location: Wayne Thompson CTL Thompson April 23, 2014 Wolverine Publishing 316 Willow Street Design Procedure Form: Rain Garden (RG) Sheet 1 0f 2 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, I, I, = 56.0 % (100% 9 all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = I,/100) i = 0.560 C) Water Quality Capture Volume (WQCV) for a 12-hour Dram Time WOCV = 0.18 watershed inches f WQCV= 0.8 • (0.91. ia- 1.19 • i'+ 0.78 • it D) Contributing Watershed Area (including rain garden area) Area = 7,945 sq N E) Water Quality Capture Volume (WQCV) Design Volume Vwocv = 118 cu If Vol = (WQCV / 12) *Area F) For Watersheds Outside of the Denver Region, Depth of ds = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWocv OTHER = cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of water Quality Capture Volume (WQCV) Design Volume VWocv USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) Dwocv = 12 in B) Rain Garden Side Slopes (Z = 4 min., honz. that per unit vertical) Z = 4.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AM„ = 79 sq ft D) Actual Flat Surface Area A,,u = 121 sq It E) Area at Design Depth (Top Surface Area) Ars, = 121 sq ft F) Rain Garden Total Volume Vr= 121 cu ft (VT ((AT. + Aru ) / 2) ' Depth) 3. Growing Media Choose One Q 18" Rain Garden Growing Media Q other (Explain): 4. Underdrain System Choose One A) Are underdrains provided? O YES Q NO B) Underdmin system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y= N/A ft Volume to the Center of the Orifice it) Volume to Drain in 12 Hours Vol,. = N/A cu ft III) Orifice Diameter, 3/8" Minimum DU = WA in UD-BMP_v3.03, RG 4/2312014, 10.09 AM Design Procedure Form: Rain Garden (RG) Sheet 2 of 2 Designer: Wayne Thompson Company: CTL Thompson Date: April 23, 2014 Project: Wolverine Publishing Location: 316 Willow Street 5. impermeable Geomembrane Liner and Geotexble Separator Fabric Choose One O YES A) Is an impermeable liner provided due to proximity NO of structures or groundwater contamination? G Inlet / Outlet Control Choose One 0 Sheet Flow- No Energy Disstpabon Required A) Inlet Control Cancen[2tetl Flow- Energy Dissipation Provided Choose One i Vegelafion 0 Seed (Plan for frequent weed control) 0 Plantings 0 Sand Grown or Other High Infiltration Sod 8. Irrigation Choose One (9 YES NO SPRINKLER HEADS ON FLAT SURFACE A) Will the rain garden be irrigated? 0 NO Notes: UD-13M'P_vI03, RG 2014, 10:09 AM