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HomeMy WebLinkAboutDrainage Reports - 05/29/2018June 28, 2016 Basil Harridan, RE-., CFM Stonmwater Quality Engineer Fort Collins Utilities, Stormwater 700 Wood Street Fort Collins, CO 80521 JVA 6xotpaatad 25 Old Taws Square Ci/tyof,JroFort Collins AppTjved Plans Suite 200 Apf loved by.'A— NOT eVit;WJIEX� FatCC1M COB0524 r+ 74 S70f2..MMJ:�TE� 970.225.9D99 D*: �-&4 ZOIT 7 infooivarva-wm RE: City of Fort Collins Gardens on Spring Creek — Drainage & Erosion Control Memo JVA Job No. 2257c Dear Mr_ Hamdan: www4va1va=I% This letter has been prepared to summarize the drainage concept, solutions and changes in impervious area associated with the site improvements for the Gardens on Spring Creek project located at the Community Horticulture Center, 2145 Centre Avenue, Fort Collins, Colorado. This letter represents an addendum to the Center for Advanced Technologies 2211 Filing ("Community Horticulture Center") Final Project Development Drainage and Erosion Control Report, dated January31, 2003, prepared by EDAW, Inc. (EDAW). Overview The existing 18.3 acre site consists of the Community Horticulture Center (CHC) and outdoor classrooms, visitor parking lot, Children's Garden, Garden of Eatin', Experiential Garden, and the Rock Garden, all constructed as part_ of the first phase of the Master Plan for the development of the City -owned property. In general, as part of the final buildout of the project (phase 2) on the remaining 5+ acres of undeveloped land, proposed improvements include the addition of the Great Lawn and bandstand/stage, the Prairie Garden, Foothills Garden, Undaunted Garden, extensive trail system expansion, and enlargement of the storinwater detention pond/Wetlands Demonstration Site to the east. The project site is located in the FEMA 100-year regulatory hoodway and City. of Fort Collins Spring Creek Drainage Basin (SWMM Subbasin 130), and no stormwater detention is required (refer to the project Floodplain Memo prepared by JVA, Inc. dated September 8, 2015 for compliance with Chapter 10 of City Municipal Code: Flood Prevention and Protection). The referenced Final Drainage and Erosion Control Report for the project accounts for the anticipated phase 2 buildout of the gardens and corresponding increase in runoff into Spring Creek. This letter will serve to supplement the original report and demonstrate that the final'development of the Gardens on Spring Creek complies with the approved stormwater drainage plan designed by EDAW. Existing Drainage Design As discussed in the approved drainage report, the predeveloped site historically drained overland directly into Spring Creek. The original storm design by EBAW mimics the historic drainage pattern; runoff from the site flows via curb & gutter (in the existing parking lot), grass swales, culverts, and through a perforated underdrain system within the water quality porous landscape detention areas, ultimately discharging into Spring Creek. The southern portion of the site is interrupted by the Sherwood Ditch Lateral, and the original suspended CMP storm culverts were replaced with RCP culverts underneath the ditch to convey runoff into Spring Creek as part of the phase 1 project. Other than the area immediately adjacent to the Sherwood Lateral, no runoff will enter the ditch except in the I00-year event. BOULDER FORT COLLINS WINTER PARK GLENWOOD SPRINGS DENVER CoFC Gardens on Spring Creek Drainage Memo June 28, 2016 ' 2 of 2 Proaosed.Draina¢eDesian--•-------_.- - -" The drainage characteristics of the phase 2 buildout of the Gardens on Spring Creek comply with the original stormwater design intent as described in the approved drainage report and no major variations are proposed. Runoff will continue to be conveyed to Spring Creek via a combination of overland flow, Vegetated swales, and perforated piping. The existing constructed wetlands basin (previously referred to as the Wetlands Demonstration Site) will be expanded to approximately 15,000 square feet of area and 0.491 acre-feet of volume. This enlarged basin will encompass and replace the existing southeastem porous landscape detention (PLD) area (identified as water quality basin Ala in the original Report) while retaining the existing concrete sill structure and downstream PLD area to the north, eventually outfalling into Spring Creek. The wetlands basin will provide 11,843 cubic feet of storage volume above the permanent water surface created by the concrete sill at an elevation of approximately 4990.94 feet (NAV088 datum), an increase of 8,149 cubic feet over the existing condition. The small PLD area to the north referred to, in the original plans as basin Alb will also remain. See the attached grading plans, sheets CLO-C1.2. EBAW's Report anticipated the Gardens full buildout by assuming an overall runoff coefficient value of 0.35 and an approximated 10% imperviousness. Based on as -built drawings, of the Horticulture Center, the existing/post-phase 1 overall site imperviousness was calculated to be 12.5%, with a coefficient of 0.40. The. Gardens final proposed layout was calculated to be 17.8% and 0.44 respectively, resulting in a minor increase over the existing and an insignificant deviation from the original assumptions. The associated increase in runoff is more than offset by the increased volume in the constructed wetlands basin. See attached calculations. Erosion and Sediment Control During construction; temporary erosion and sediment control practices will be used to limit soil erosion and sediment discharge off the site. An erosion and sediment control plan with stormwater management plan and details will be provided in the utility plans for construction. Refer to the Erosion Control Report prepared by JVA dated June 28, 2016. Please feel free to contact myself or Karen Brigman to discuss any questions you may have. Sincerely, JVA, INCORPORATED By: Brian ell, P.E. Regio al onager to � � YPejP Wd lO 00 NOISONR QW,30tl INWONIMO N c p u I v s t 1 sN ALlINItlNP-R WON3W HGNW tl3LN3 wuinouiw"NNWW00 illl v I eH nunla nun. immmuni, nanwrnrmuna auluxl QD 3 / � 15 b 6Y I M a v I& ' 5 & Ali A 1 l � I I a YYY % W V Aw q.d %e =g6 a1� n •• vaala 1S3h1-NV1d `JNIOtltlO 11311tl130 :I� v e R !vrVW v ° ° `� ° SIN Noo .- U -> I,77S ' 33'.,13� WnOIINOHWwN Wn v Cva 9Nnu ONZL A903mom cgow wA 3N o E a E a j 60 Z'M 133HS 33S - 3NIIH31tlW _�__ _ € e . I -- - Ytd�B 1SV3-Ndld ONIQYtl0031fI130 9 N ! p 6 e u SWdA 1W T Jd-1 "ON3WNMONW ¢ Q ii!! v e8 num�nun /mm�uunai nanuenrrvuna auiva� JVA Incorporated 25 Old Town Square Fort Collins, CO 80524 Ph: 970.225,9099 Fez: 970.225.6923 Gardens on Spring Creek Historic Runoff Coefficient Calculations Location: Fort Collins Minor Design Slo,m: 2 Major Dealgn Storm: 100 Soil Type: GO Job Name: Garden. on Spring Creek 1% oa C5 co coo Job Number: 2257c 5v.n P...d 190% 0.05 aoo 0.95 too Data: 9115115 C... Cft s sea 90% 0.0 000 DID IAa By: KRB Roor We ON 000 0.95 1.00 G•.M 40% am ON 0.50 000 L•ntlerapn0(8 WO 0% 0.15 GIN Ods O.IO land.c.pna(CM .do a% O35 ON O,ri 031 PlayOrouna 10% 0,11 ON 0.11 014 AmnclalTurf 25% 020 0.00 020 025 Basin Desl in Data I (%) • 100% 90% 90% 40 % 10% 25 % 0% 0% 1 (%) Runoff Coeffb A-s.d Al.p. la Akc.P. Basin Design Add..wc A,..y AD.., AolyOnd A.n.mn ATo1a1 AT.,., Imp C2 CS CIO C100 Name Point .".a(s0 (� (� (� lap .ma (C10.11) (� lad (%) (sp (� can H 1 49.942 39,309 10,331 12.087 5,900 678,427 795,998 1 10.27 12.5% 0.34 0.00 0.34 0.40 2257c- Rational Calculalions.Asz Histonc C Page i of JVA Incorporated 25 Old Town Square Fort Collins, CO 80524 Ph: 970,225,9099 Fax: 970.225.6923 Gardens on Spring Creek Developed Runoff Coefficient Calculations Location: Fort Collins Minor Design Storm: 2 Major Design storm: 100 Soil TypeCID Job Name: Gardens an Spring Creek 1% c2 cs m0 ClOO Job Number: 2257c indent Pdeatl 100% 0.05 D.00 0.95 Ise Date: 9/15115 D°0ar11° DMnMluae 90% an ono 0.95 1DO By: KRB R°°r so% On 000 O As t oo. Dmel 40% 0.50 DAO 0.50 0.0 Un0.ueplM 1p.do OM 0.15 am 0,15 0.19 Len4edepa9 (GN "o 0% on ON O.n 0.31 Pidegai M 10% 0.11 0.00 all sI4 Audi Tun n% am ON 020 am Basin Desire Data I (%) - 100% 90% 90% 40 % 10% 25% 0% 0% 1 (%) Runoff CoeRs Basin Design AwV°u Addwc A1OOr AIW.d Ann. turf Antwwle Ant°ew ATm, Aim, imp Name Paint .(dent ° ° (� (so r+ve1 (at) (so (30 wo ( "") lm (m) (%) C2 CS C70 C1O0 (ep (at) (30 D 1 49,942 79,073 10,817 27,864 5.900 622,400 795,996 18.27 17.8% 0.38 0.00 0.38 0.44 2257c- Rational CaiwlationsAint Developed C Page 1 of 1 Gardens on Spring Creek Critical Pond Elevations Design Engineer: K. Brigman Design Firm: JVA, Inc. Project Number. 2257c Date: September 9, 2015 DESIGN CRITERIA Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001 Stage Storage Volume (pond volume calculated using the prismoidal formula): V_(A,+A,+ A,A,Depth 3 CONTOURIFn AREA(Fl°) AREA(ACRE) VOLUME tACREFT) OEM(FT) CUMULAUVEVOLUME (ACREFn CUMULAIiVEVOLUME ICUSIC Fn 49E7.so 000 0000 0000 0.00 DIM 0.00 498e.o 790,00 0.018 0.003 0.50 0.003 131,67 4989.0 1 <Eo.00 0.034 0.02e 1.50 0.029 120 n 4990.0 4,200.00 0.09E 0.083 2.50 0,091 3973.16 4990.94 7,860.00 0,180 0.128 3.44 0.219 9552.25 4991,0 8,075.00 0.185 0.011 3.50 0.230 10030.29 4992.0 15,010.00 0,345 0,261 4,50 0.491 21395D7 4992.5 tFkPA�D F 4992.00 4991Ao Z 499000 6 4989.00 W 49EE.00 4997 00 DETENTION POND VOLUME VERSUS ELEVATION nn nt n2 03 04 0s 0i DETENTION POND VOLUME (AC -FT) 'Permanent WSE 2257c Pond Calcs.xls - Pond Stage Storage #1 JVA, Inc. 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GARDEN l i : //i . , /' / / / / I / / /i l i ; `� ```i N W YLa Q~ // / iii/i/// //aY jlll YwL W . , , , // _ NaW 1 j /'\ �' �'/i//ly L/ / iI/I i i/'/I '' II/ i ow~ Z I IF If it / �y / I I ii/''p .W a x e0 ' it / / LQtS� / ' I / / /' , /' / scNE Ix ffEt F- U LL z / Ii/,� I i i it /„/ I H OUMW to //i `y ,i i i i i i /i/ / / Z w 1 \ ,I i, I I / I , i. 1 DISTING /I '''i ' / ' / i / i i i ' i / / ' / < � m Q 9§ i PARKING LOT / /ii' /� I' `—' / i i i , , �'/' / i i Ci M Q w 1 I / / / ,. /, / O p i / i f' i iii / ` LL 0 p /iii jii/,/ `\ i i sxtEt xweea If „ / c. C1.2 City of For1/1 It If I of It t Collins, Coloradit: CD o UTILITY PLAN APPROVAL rwrxovEo: crrueM.. oN CHECXED BY: H1b6NLenbll� LXECIQD BY: e�rub pb cnEClao BY: n.iW emx� or cxscxeo er: v.n.wroo.uo� oN cHECIao er: r..w.i.rxw.. d. cHEcxEo er: