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Home My WebLink AboutSEVEN GENERATIONS MULTIFAMILY - FDP230008 - DOCUMENT MARKUPS - ROUND 2 - DRAINAGE REPORT FINAL DRAINAGE REPORT FOR Seven Generations Multifamily Prepared by: Highland Development Services 6355 Fairgrounds Ave, Suite 100 Windsor, Colorado 80550 Phone: 970.674.7550 Prepared for: Black Timber Builders 417 Jefferson Street Fort Collins, CO 80524 Office: 970.657.2399 March 1, 2023 Job Number 22-1057-00 Page 3 STORM DRAINAGE CRITERIA This preliminary drainage report was prepared to meet or exceed the City of Fort Collins Stormwater Criteria Manual. The Criteria Manual and amendments to the Urban Drainage Flood Control District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were referenced as guidelines for this design. HYDROLOGIC CRITERIA The rational method was performed to calculate the peak runoff rates for each basin. Percent imperviousness and runoff coefficients were calculated for each basin using the surface characteristics of each basin. The time of concentration was calculated using City of Fort Collins initial time of concentration and the intensity was calculated using the corresponding storm rainfall depth and the City of Fort Collins’ Intensity-Duration-Frequency Curve. The City of Fort Collins area has a 2-yr, 1-hr rainfall depth of 0.82 inches and a 100-yr, 1-hr rainfall depth of 2.86 inches. These depths do account for the 1999 adjusted rainfall depths. The proposed redevelopment rational calculations are compared to the pervious rational calculations to review the impacts of this proposal. HYDRAULIC CRITERIA The existing storm drainage system was analyzed to confirm conveyance capacity of the minor 10-yr event. The major 100-yr storm event is conveyed through the combination of private drives, storm sewer pipes and swales. Runoff flows determined with the rational method will be attenuated through the site. Inlet capacity was confirmed utilizing the manufacturer capacity charts. All swale and pipe outlets will be protected with riprap or suitable erosion protection methods. Storm sewer pipe outlets will be protected using the requirements set by the USDCM for the protection downstream of culverts. All supporting calculations are located in the Appendix. Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA Low Impact Development Summary Sq-Ft Acres Impervious Area (sq-ft) % of Impervious Area Requiring Treatment Impervious Area Requiring Treatment 55,874 1.28 6,385 75% 4,789 LID Facility Contributing Basins Area Drainage to LID (sq-ft) % Impervious Impervious Area Treated (sq-ft) WQCV12-hr (watershed inches) WQCV12-hr (cu-ft) Treatment Method 1B 1B 42,894 77.6% 70,846 0.25 898 Storm Chamber 4,789 70,846 1479.4% Area (sq-ft) Area (acres) Treatment Ratio 42,894 0.98 96.3% 1,665 0.04 3.7% 44,559 1.02 Seven Generations Multifamily Low Impact Development Total % Required Treatment Development Area Breakdown City of Fort Collins - Ordinance No. 007, 2016 - Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or - Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are permeable. Impervious Area Treated (sq-ft) Impervious Area Required for LID Treatment (sq-ft) LID Treatment Summary LID Treatment Areas J.Claeys Highland Development Services 22-1057-00 March 1, 2023 Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016) Description Total Redeveloped Area Total Improvement Area Water Quality Area Treatment Summary Description Total Area Treated by LID Total Area unable to be Treated Allowed FilterFabric Flow Ratea(cfs)0.35 gpm/sq-ftSC-106LP 14 10 6 6 85.4 25 12 14.8 0.012 6.9 15.0SC-310 18 8 6 6 85.4 34 16 20.2 0.016 14.7 31.0SC-740 18 8 6 6 85.4 51 30 30.2 0.024 45.9 74.9DC-780 18 12 6 9 85.4 51 30 30.2 0.024 46.2 78.4MC-3500 24 8 12 9 90 77 45 48.1 0.038 109.9 178.9 14.9 46MC-4500 24 7 12 9 52 100 60 36.1 0.028 106.5 162.6 35.7 108.7LIDFacilityChamberTypeTotalRelease Ratef(cfs) WQ Flowg(cfs)Req'd StorageVolumeh(cu-ft)Minimum No. of ChambersiChamberStoragej(cu-ft)No. ofEndcapskEndcapStoragel(cu-ft)Total ChamberVolumem(cu-ft)Total InstalledSystem Volumen(cu-ft)WQCV12-hr(cu-ft)1B SC-106LP 0.55 0.95209 48 329 4 0 329 926 898NegligibleEndcapVolumed(cu-ft)Min InstalledEndcap/AggregateVolumee(cu-ft)NegligibleNegligibleNegligibleMin InstalledChamber/AggregateVolumec(cu-ft)Seven Generations MultifamilyLow Impact DevelopmentStormTech Chamber Configuration SummaryStormTech Chamber DataDesign Engineer:Design Firm:Project Number:Date:Length(in)Width(in)Height(in)Floor Area(sq-ft)ChamberVolumeb(cu-ft)MinAggregate Base(in)Min Aggregate Cover(in)Max Cover(ft)Min Cover(in)ChamberModelJ.ClaeysHighland Development Services22-1057-00March 1, 2023Note:a. Release rate per chamber, limited by flow through geotextile with accumulated sediment. City acceptable flow rates determined to be approximately 1/2 of the Nov-07 Qmaxfrom Figure 17 of the "Final Report on Field Verification Testing of the StormTech Isoloator Row Treatement Unit", prepard by the University of New Hamphire Stormwater Center, dated Setpember 2010.b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.d. Volume within endcap only, not accounting for void spaces in surrounding aggregate.e. Volume includes endcap and void spaces (40%) in surrounding aggregate, per chamber unit.f. Release rate per chamber times number of chambers. This is used as the allowed release rate for the FAA calculations.g. WQ flow, equal to 1/2 of the 2-yr peak runoff rate, referenced to size flow control structure.h. Required detention volume determined using the FAA Method based on the acceptable release rate of sediment accumulated filter fabric of the chambers and the 1/2 of the 2yr in flow rate.i. Number of chambers required to provide required FAA storage volume stored within the chamber and endcaps only (no aggregate storage).j. Total volume provided in chambers only (no aggregate storage).k. Number of endcaps based on desired chamber layout.l. Total volume provided in endcaps only (no aggregate storage).m. Total chamber and endcap storage (not aggregate storage). This number must meet or exceed the required FAA storage volume.n. System volume includes total chambervolumeplus surrounding aggregate volume,assumes a 40% void ratio for aggregate storage.This totalis provided from ADS Design Tool. DESIGN CRITERIA 0.83 1.00 0.83 ft3 acre-ft 0.99 acres 209 0.00 0.55 cfs Time (min) 1/2 2-yr Intensity (I , in/hr) Q100 (cfs) Accumulative Runoff Volume (ft3) Accumulative Release Volume (ft3) Detained Volume (ft3) Detained Volume (acre-ft) 0 0.000 0.00 0 0 0 0.00 5 1.425 1.17 350 166 183 0.00 10 1.105 0.90 542 333 209 0.00 15 0.935 0.76 688 499 189 0.00 20 0.805 0.66 790 666 124 0.00 25 0.715 0.58 877 832 44 0.00 30 0.650 0.53 957 999 -42 0.00 35 0.585 0.48 1,004 1,165 -161 0.00 40 0.535 0.44 1,050 1,332 -282 -0.01 45 0.495 0.40 1,093 1,498 -406 -0.01 50 0.460 0.38 1,128 1,665 -537 -0.01 55 0.435 0.36 1,174 1,831 -658 -0.02 60 0.410 0.34 1,207 1,998 -791 -0.02 March 1, 2023 Design Engineer: Design Firm: Project Number: Date: #SPILL! WQ Treatment Volume - FAA Method J.Claeys Highland Development Services 22-1057-00 Adjusted Runoff Coefficient (CC f ) Area (A ) Allowed Release Rate - City of Fort Collins - Storm Water Criteria Manual - City of Fort Collins accepts 1/2 of the 2-yr runoff as the WQ inflow rate WQ Treatment Volume Calculation - 1B Filtration Chamber Runoff Coefficient (C ) Frequency Factor (C f )Required Detention