The URL can be used to link to this page

Home My WebLink AboutDrainage Reports - 07/11/2017February 17, 2017 Mr. Wes Lamarque City of Fort Collins Storm Water Utility 700 Wood Street Fort Collins, CO 80522 Re: Maple Hill Park ICG Project No. 1165-012-89 Dear Wes, INTERWEST CONSULTING GROUP City of Ft,. Collin rov „ Plans �►Ppmved By Date Please accept the following letter report on behalf of The City of Fort Collins Park Planning and Development to demonstrate the site's compliance with the previously approved Final Drainage Report for Maple Hill Subdivision, as prepared by TST Consulting Engineers, dated March 26, 2003. INTRODUCTION The proposed park is legally known as Tract I of Maple Hill Subdivision and is 7.14 acres. The park is bounded on the north by Maple Hill Drive, the east by Bar Harbor Drive, and existing single family homes on the west and south. The majority of the park currently drains to an existing low point located near the eastern property line. The original runoff coefficient calculations and stage -storage table are attached for reference and all detention and water quality requirements for this site have been met by the overall Maple Hill development. EXISTING CONDITIONS The site is currently vacant and contains a stand of natural grasses. The Overall Drainage Plan that was included in the previously approved Final Utility Plans for Maple Hill designates the park area and the back yards of the surrounding single family homes that are tributary to the park as Basin B13. This basin drains to a low point on the park property where it is collected by an area inlet. The area inlet is connected to the storm system that discharges into the existing water quality and detention pond located just east of Bar Harbor Drive. The northeast and southeast corners of the park property are designated as portions of Basin B9 and B 14, respectively. These areas sheet flow directly onto Bar Harbor Drive and are collected by the existing storm system which discharges into the existing pond. Basin B 13 has a minor storm runoff coefficient of 0.28. Mr. Wes Lamarque February 17, 2017 Page 2 of 2 PROPOSED DEVELOPMENT The proposed park primarily follows the original drainage patterns described in the original plans. Basin 1, 2 and 3 make up the park property. Basin OS accounts for the off -site tributary area that was originally included with Basin B 13 from the approved plans. Basin 1 and 3 continue to sheet flow directly on to Bar Harbor Drive as initially intended; however, these basin areas are slightly increased. Basin 2 and Basin OS drain to a low point in the park which is the proposed irrigation pond. This pond will be fed by a proposed raw water connection from the existing irrigation main located off -site. All stormwater runoff from Basin 2 and Basin OS will sheet flow directly into this pond. A Type C inlet structure will be placed 6 inches below the top bank of the pond setting the permanent water surface elevation to 5009.50. This inlet will be connected to the existing area inlet (which will be replaced with a proposed manhole) and be conveyed to the existing storm system which outfalls to the existing pond constructed with the subdivision. Basin 1, 2, 3 and OS have a combined minor storm Runoff Coefficient of 0.23 which is less than the Runoff Coefficient for Basin B13 (0.28) from the approved plan. Therefore, it is requested that the site be deemed in substantial conformance with the previously approved Final Drainage Report. Please see the attached excerpts from the Maple Hill Subdivision Final Drainage Report detailing the assumptions and original flow calculations for the park area. LOW IMPACT DEVELOPMENT REQUIREMENTS Runoff reduction practices (LID techniques) are also required. No less than seventy five percent of any newly added impervious area must be treated using one or a combination of LID techniques. The development of the park adds 28,857 sf of new impervious area. Approximately 81% of that area (23,303 sf) will sheet flow over a grass buffer prior to entering the irrigation pond. City Stormwater has confirmed that the LID requirements are met with the grass buffers and the wet irrigation pond. The new impervious area and turf areas will be treated with these two methods. It is also important to note that there is no pavement or pollution producing impervious area associated with this project. Additionally, any suspended solids associated with the runoff from the park will be captured in the irrigation pond prior to exiting the site via the proposed Type C inlet. If you have any questions or comments please contact me at (970) 460-1091. Sincerely, S ylar Brower, P.E. Colorado Professional Engineer 44248 � � I _ --- --- --- — — — — _--------_ ----_ ------------------------------------------------ W __W —w S W W W W W W W W W W W — W �y xb,ypw MAPLEFI/LL DRIVE rx er',eow s —s s s s s • s• —s i S - p i — s - 5 i i i i i p i i ii i i p_i i ----------------G------�—_ I ------—ram— rnnetnaeMn Summnro rhaw (Constrouvo PhusO) Mabiluonan Onr i TIP Grade Subgmtle Pann9 W.dFape DenebilN,alioo Best Management Practices (BMPs( _ kruttwtl'FMaNtbn' comes«ee aerm• ___ - --- Tnntour furrows IRPPng / Dlskinel SedlmM171.1 / Hlter Ven.clt TracFnF Pad• Contrett waseaw• Row Barriers Iwan"l l• kre mNnw D,e...... R., RaP _ — 'All BMPs to Ee Removed once Consn Rtlon s ComPlele. Mgetww Temporary 5eMng Plznnng Anytime@e site will sildolment lon er Than 30 Days Multhing/SUI.nI Any tlmelhesile Wlll sit dprment Doer than M Days Pnm..enl SeMng Plzntng Rolled Prodat[S I ngTBOnkas/Mats Anytme thesile will sit 0rmentl0n erthan30Days EXISTING LOCq p =�COND Tgq 9pBASIN DESIGN pi TOTAL AW Irl R Al. AREA n) ROOF AREA IW n) FAV® AIE URnI SCEYfALK AREA ISV nI UkNE AISy laR nl RIFF ry$E (C) % FPMAR F RKS t 103 M.45 0 0 STO 43ws 01, 1 z Sm Zaa1M 0 0 27VI 2Xa13 Oro 10 3 ON 10.08 0 0 No e.32 ota 9 RaATdal 714 3110.97 0 0 29 mT 2m.2W Ole 9 as 1 A 71.2+9 30,d00 0 0 .34+9 015 37 Ass ml Rod All ON E3 hon e T Al- las igAma 24am a 2aan 325,641411 "3 10 40 20 0 40 Bo SCAIf t"- 40' LEGEND ~ fRiOPO`£O aRERION ROW OG OVERtANO V EHICLE TRACKING CONRVOL OCCONSTRUCTON Y1C EMRMICp ® coNCRETE wASHarr 0 i tMLT FENCE CD IP-1 � INIET PROT'CTON4TYFF i� O® wATTL£ O® GRAD -BAG - FROPOS'ED DRAINAGE BASINONIDEUNE A 0.3 .6 y nRAINAGE.. NUMBER MINOR STJRM RDNOFF GOEFFIGIEYI DRANAGE BA4NAREA PnGPo�aRECTaN aF ovDa.ANo Row N N lD O 1n w m Z mO'00m �aMm N O U zO O N 4 o C Q O p N W 4 O f U I p EL Lie =Nmn w w I zw(y) D �OO LL V t Ua N O tL � � Y NOTES: Q w a 1 CONiAACTOR TO PROVIDE AND MAINTAIN ALL NECESSARY EROSION CONTROL MEASURES PRIOR I L I Q J ANDTHROUGHOU'CONSTRUCTION. PLACEEROSION Z CONTROL PROTECTION Al ALLEASRNGINLETS F J OOWNSTFEAMION FROM THE CONSTRUCTION PREA EROSCONOTE TROL PRCTION SHALL REMAIN IN W PLACE UNRL CONSTRUCTON IS COMPLETE AND ALL DISTURBED GROUND IS ADEQUATELY VEGETATED WLT 1 O W OWNER'S APPROVAL FOR REMOVAL (r. 2. THE EXTENT OF EROSION CONTROL PROTECTION (L ^ BHALL BE OBSERVED AND ADJUSTED AS NEEDED DURING CONSTRUCTION BASED ON STTECONDLUONS . I.L a AND THE PERFORMANCE OF THE EROSION CONTROL CONTROL MEASURES SHOWN, TO SUPPLY SUFFICIENT EROSION CONTROL AND MINIMRE DOWNSTREAM WATERWAY POLLUDON CALL UTILITY NOTIFICATION CENTER OF COLORADO 811 CALL 2-81)SINESS DAYS IN ADVANCE BEFDRE YOU M. GRADE. OR EXCAVATE r m (11 FOR THE MARKING OF UNDERGROUND ' MEMBER UPUTMS. IN = s m w m w 0 Dl 0 w U CITY OF FORT COLLINS, COLORADO UTILITY PLAN APPROVAL APPROVED: OIY EIrI HER DATE CHECKED BY: WATER R WASTEWATER UTIUTY DATE CHECKED BY: STOR1.111I UTILITY DATE CHECKED BY: PARKS h RECREADON DATE PRI NO.1116150126 CHECKED BY: TRAFFIC EMDREER DAZE C OF 10 V CHECKED BY: DATE Irlterwest Consulting Group RUNOFF COEFFICIENTS & % IMPERVIOUS L.00A110N: Maple Hill Park PROJECT' NO: 1165-012-69 COMPUTATIONS BY: sb DATE: 1/102017 Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I Type B Soils Streets, parking lots (asphalt): Sidewalks (concrete): Roofs: Gravel or Pavers: Lawns, sandy soil (Flat <20/6) : Runoff % coefficient Impervious C 0.95 100 0.95 96 0.95 90 0.50 40 0.10 0 SUBBASIN DESIGNATION TOTAL AREA (W) TOTAL AREA (sq.8) ROOF AREA (sq.q) PAVED AREA (sq.8) SIDEWALK AREA (sq.R) LANDSCAPE AREA (sq.0) RUNOFF COEFF. (C) % Impervious REMARKS 1 1.02 44,495 0 0 570 43,925 0.11 1 2 5.88 256,144 0 0 27,271 228,673 0.19 10 3 0.24 10,448 0 0 1,016 9,432 0.18 9 Park Total 7.14 311,087 0 1 0 28,857 262,230 0.18 1 9 Gs 1.70 74,216 1 30,800 1 0 0 1 43,418 0.45 37 Assumed Roof Area for Ex homes TOTAL 8.85 305,305 1 30,800 1 0 28,857 1 325,618 0-23 10 Equations - Calculated C coefficients & % Impervious are area weighted C=E(Ci Ail /At Ci = runoff coefficient for specific area, Ai Ai = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider At = total area over which C is applicable; the sum of all Ai's Final FLOW(Ot-10-17).xls P ti M1 V ✓� ppp/---YYY'111 b b ry N N N- G - N r V1 N V N M r� N U m bra �a:�-aaa::sxaa$�saa <��__rn;Nm-rPa arsa�a� - t- 0 s.� ^^ �.:� m!Ia $ s ri yy 9q �i g s Si �m o`. . a ^ «a� > M N ^_ O O I•f m _ r N N N 'G P m P N b /'� - m n P P p iO „ S r �O S i •O 'OO O r� n v^i O«^ ^ O 8 « 8 m m P« 2 w ryO i i O O n N N O O n . O Ci n w1 r1 w1 r rn n. � O � 3 �� E n�aosa„„asv :g;8=a----ga r; r�asax�ra 0 ^ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - h h yV pVZt J O 8888888888.8885$888.5 88------------- 888888888 p o c coo d c o o d o o d d o 0 o a o 0 0 o d d d o o d o d d d d 0 O C o 0 0 0 0 0 0 a V �mq�:smoaa.s.�::?m2�" �a�oa�ryry,�s:ss> ndaTa .�� a - ., s a o a a o.- F N O o o G N C A � uU--u N Z < < m u LC Za UU w unofficial copy was downloaded on Jul-30-2015 from the City of Fort Collins Puhlic Records Website: htip://citydms.fcgov.com