HomeMy WebLinkAbout14 - Design Report - South University District Ph 1 & Stadium View Apartments - StormwaternrStorm Water PlanSouth University District - Phase 1, andStadium View ApartmentsFebruary, 2014Submitted to:City of Bozeman Engineering Department20 East OliveBozeman, MT 59715Prepared by:Stahly Engineering and Associates7585 Shedhorn DriveBozeman, MT 59718(406) 522-9526^"^^yEST.STAHLY^^^^^iiT^
nStorm Water PlanContentsGeneral InformationExisting Conditions and General Design CriteriaStorm Drainage Plan DescriptionEstimation of RunoffPre-development Runoff- Phase 1Post-development Runoff- Phase 1Pre-development Runoff - Phase 2-3Post-development Runoff- Phase 2-3Storage/Treatment FacilitiesOutfall Structure Weir SizingCurb and Gutter CapacityInlet CapacityFacilities MaintenanceFigures and TablesFigure 1. Inlet Basin ExhibitTable 1. Runoff Calculations - Phase 1Table 2. Runoff Calculations - Phases 2-3Table 3. Outfall Structure SizingTable 4 Curb and Gutter Capacity CalcsTable 5. Phase 1 Inlet Basin and Pipe Capacity CalculationsTable 6. Phase 1 Detention Basin CalculationsTable 7. Phase 2 and 3 Detention Basin CalculationsStorm Water Plan12/6/2014
nnGeneral InformationThe South University District - Phase 1 subdivision is located within the City ofBozeman adjacent to South 11th Street and south of Kagy Boulevard. Thesubdivision is located west of Bobcat Stadium and is south of the existingStadium Center Subdivision. The subdivision consists of 3 lots, road right-of-way, and park. Lot 1 is a proposed 9.82 acre site for the Stadium ViewApartments, a 499-bed student housing facility which is currently under review.Storm drainage improvements include those required for public streets installedwith the Phase 1 South University District subdivision as well at improvementsserving the Stadium View student apartments located on Lot 1 of the subdivision.Storm drainage improvements also include backbone infrastructure servingfuture phases of development to the west and south.The developer's contact information is:Fountain Residential Partners2626 Cole Ave, Suite 620Dallas, TX 75204Existing Conditions and General Design CriteriaThe existing condition at the site is undeveloped agricultural land. Down-gradientdevelopment has restricted storm drainage paths leaving the property to thenorth. An existing creek (Mandeville Creek) runs along the west edge of Phase 1and is the only acceptable location for storm water to leave the site. MandevilleCreek continues to flow north through the City to the East Gallatin River.In accordance with the City ofBozeman Design Standards and SpecificationsPolicy (COB Standards^ an engineering analysis has been conducted for theSouth University District (SLID) property to limit post-development runoff to pre-development rates. Storm runoff originating on the site will be detained on-siteand released at rates less than the pre-development rates. Furthermore,detention basins will reduce storm water velocity and allow solids, silt, oils,grease, and other pollutants to settle from the runoff before the flows leave thesite.Inlets and storm sewers are sized to pass the 25-year event without overtoppingroadways. Should a larger event overtop the roadways grading will divert stormwater away from structures.Storm Water Plan22/6/2014
n0Storni Drainage PlanThe overall storm drainage plan for SLID - Phase 1 and Stadium View isdepicted on Figure 1 at the end of this report. Overall drainage direction on theproposed development is indicated by arrows showing the proposed drainagepatterns and inlet locations.Estimation of RunoffRunoff estimates are provided separately for Phase 1 (Lots 1 and 2) and Phases2 and 3 located south of Phase 1 on Lot 3. Phase 1 is 16.7 acres. Phases 2 and3 combined are 37.98 acres.The rational method was used to estimate peak flow rates and volumes fromstorm runoff. Standard assumptions in using the rational method include thatrainfall is uniformly distributed over a watershed for the duration of a storm event,the peak runoff rate occurs when the storm duration equals the time ofconcentration, and the runoff coefficient for a watershed is constant for similarland use. Time of concentration was determined from the slope of the basin,rational runoff coefficient and flow length (COB Standards - Equation II.E.6).Pre-development Runoff - Phase 1A runoff coefficient of 0.20 for open land was selected for pre-developmentconditions. An average overland slope of 2.1% over a basin length of 1,650 feetprovides a time of concentration of 53.4 minutes. The Bozeman IDF curvesshow a rainfall intensity for the 10-year design storm event of 0.69 in/hr.Applying this over the 1 6.7 acre site produces a runoff flow rate of 2.31 cfs at thedownstream end of the basin.P^st-development Rynoff- PhaserPost-construction runoffwas calculated using a runoff coefficient of 0.60(commercial neighborhood) to account for future site development in accordancewith the master plan. Although Lot 2, the future development area (5.00 acres)on the west side of Phase 1 will not be developed initially, the anticipated runofffrom this lot (using commercial neighborhood inputs) was accounted for in thedesign and runoff calculations. The increased impervious area reduces the timeof concentration to 15.0 minutes. The Bozeman IDP curves show a 10-yearstorm intensity of 1.57 in/hr. The rational method provides a 10-year peak runoffrate of 15.78 cfs. The same analysis for a 25-year event provides a peak runoffrate of 20.58 cfs.Storm Water Plan32/6/2014
n0Table 1 Runoff Calculations - Phase 1Pre-development | Post-DevelopmentPost-DevelopmentLand UseOpen LandCommercialNeighborhoodCommercialNeighborhoodDrainage Area (acres)16.716.716.7Slope (%)2.12.12.1Overland Runoff Coefficients0.20.60.6Frequency Adjustment Factor, Cf111.1Design Storm Frequency10-year10-year25-yearBasin Length (ft)1,650423423Time of Concentration, Tc (min)53.415.013.2Intensity at Tc (Figure 1-2 pg.29) (in/hr)0.691.572.05Runoff Rate (cfs)2.3115.7820.58In addition to the overall storm runoff calculations for Phase 1, the 25-year stormrunoffflow rate for each storm drainage inlet basin has been determined basedon the drainage plan shown on Figure 1. These calculations are provided inTable 5 at the end of this report.Pre-development Runoff- Phase 2-3The storm water detention pond serving future Phases 2 and 3 will also beconstructed with SLID - Phase 1 and was therefore analyzed to size the basinneeded for this future development.A runoff coefficient of 0.20 for open land was selected for pre-developmentconditions. An average overland slope of 2.1 % over a basin length of 2,620 feetprovides a time of concentration of 67.3 minutes. The Bozeman IDF curvesshow a rainfall intensity for the 10-year design storm event of 0.59 in/hr.Applying this over the 37.98 acre Phase 2-3 site produces a runoffflow rate of4.51 cfs at the downstream end of the basin.Post-development Runoff- Phase 2-3Post-construction runoffwas calculated using a runoff coefficient of 0.60(commercial neighborhood) to account for future site development in Phases 2-3in accordance with the master plan. The increased impervious area reduces thetime of concentration to 15.0 minutes. The Bozeman IDP curves show a 10-yearstorm intensity of 1.57 in/hr. The rational method provides a 10-year peak runoffrate of 35.88 cfs. The same analysis for a 25-year event provides a peak runoffrate of 46.81 cfs.Storm Water Plan42/6/2014
nnTable 2 Runoff Calculations - Phase 2-3Pre-development | Post-DevelopmentPost-DevelopmentLand UseOpen LandCommercialNeighborhoodCommercialNeighborhoodDrainage Area (acres)37.9837.9837.98Slope (%)2.12.12.1Overland Runoff Coefficients0.20.60.6Frequency Adjustment Factor, Cf111.1Design Storm Frequency10-year10-year25-yearBasin Length (ft)2,620423423Time of Concentration, Tc (min)67.315.013.2Intensity at Tc (Figure 1-2 pg.29) (in/hr)0.591.572.05Runoff Rate (cfs)4.5135.8846.81In addition to the overall storm runoff calculations for Phases 2 and 3, the 25-year storm runoffflow rate for each storm drainage inlet basin has beendetermined based on the drainage plan shown on Figure 1. These calculationsare provided in Table 5 at the end of this report.Storage/Treatment FacilitiesSimple pond routing using the modified rational method is provided for Phase 1and Phases 2 and 3 in Tables 6 and 7 at the end of the report. This spreadsheetshows a required storage of 14,788 cubic feet of runofffor the 10-year event forPhase 1 and 36,467 cubic feet for Phases 2-3. The required storage is providedby 2 basins, one for the Phase 1 runoff and one for the Phase 2-3 runoff. ThePhase 1 pond has a bottom area of 9075 square feet and 4:1 side slopes. Thebottom elevation is 4928.00 and surface overflow to the west is provided at anelevation of 4930.50. The maximum depth is 1.5 feet, with a total volume ofapproximately 16,344 cubic feet. The pond for the future Phases 2-3development has a bottom area of 23,105 square feet and 4:1 side slopes. Thebottom elevation is 4931.5 and the surface overflow to the west is provided at anelevation of 4934.00. The maximum depth is 1.5 feet, with a total volume ofapproximately 36,500 cubic feet at this depth. The detention basins are locatedat the northwest (down-gradient) end of the site and will be vegetated with grass.Outfall Structure Weir SizingThe detention basin outflow for both the Phase 1 and the Phase 2-3 developmentis restricted by a typical control structure as depicted in COB Standards Figure A-2. Using the weir calculation equation given in Section II.D.2 of the COBStandards, the slot width of both weir structures was determined. The slot widthfor the Phase 1 pond discharge structure is 5 inches and the slot width for thePhase 2-3 discharge structure is 9 inches. These slot widths limit the dischargefrom the structure to pre-developed rates at the maximum depth of 1.5 feet.Storm Water Plan52/6/2014
n0Table 3 Outfall Structure Weir SizingPhase 1Pre-developed Runoff (cfs)2.31Weir Coefficient "C"Head (ft)Slot Width (in)3.331.55Phase 2-3Pre-developed Runoff (Q)4.51Weir Coefficient "C"Head (ft)Slot Width3.331.59In the occurrence of an event greater than the 10-year event the ponds are sizedfor, the overflow of the ponds directs flow to the west to Mandeville Creek.Curb and Gutter CapacityStorm runoffwill be collected in street and pari<ing lot curb and gutters. Thehydraulic capacity of the curb and gutter was analyzed to determine if the curbwould be overtopped in a 25-year event. The maximum 25-year event for any ofthe curb inlet basins produces approximately 2.70 cfs of runoff. The capacity ofthe curb at the lowest designed slope of 1.2% is 7.80 cfs at a depth of .15 feetbelow the top of the curb. Therefore, curb capacities in the development areadequate to carry the 25-year event.Table 4 Curb and Gutter Capacity CalcsRight-side slope X:1Left-side slope X:10.0533.00Channel bottom width (ft)Flow Depth (ft)00.350Flow Area (ftA2)Wetted Perimeter (ft)2.02411.906WidthHydraulic Radius (ft)0.0350.170Manning's RoughnessSlope (ft/ft)0.0130.012Average Velocity (ft/sec)Flow (ftA3/sec)3.857.80Inlet CapacityThe curb inlets on the roadways in the development were analyzed to ensurethey have capacity to accept flows conveyed to them without reaching a point0.15 feet from the top of the curb. The COB approved Neenah Foundry R-3067-L inlet structure has a capacity of 5.98 cfs at 0.35 feet of head (0.15 below top ofcurb). This capacity will convey the necessary flows.Storm Water Plan62/6/2014
00Facilities MaintenanceThe proposed storm drainage facilities will be operated and maintained by theproperty owner. The owner is responsible for quarterly maintenance of all stormwater facilities. The maintenance includes, but is not limited to, visual inspectionand removal of sediment from curbs, inlets, detention basins, and outletstructures as well as any necessary repairs to the facilities.Storm Water Plan72/6/2014
IS,FIsl«iIsla-Ih^____h1HStadium Center SubdivisionLJJLDETENTION BASIN APIPE 6APIPE 4APIPE 1APIPE 5APIPE 3APIPE 12A^PIPE 15A^-\^^-\^r-^--~-\rr^-/T!^\\i\\BASIN 3A27-®BASIN^A15-8sIn 70 ar-nrL ion1.03 acD\\l--^-"_--':PIPE 2AcuRBPIPE13A)UINLE1J(TW)^^'^W^^SfV — — +AS\y.32 acr^0)BASI<A^<Dnj/"%0.^</</PIPE 7Affi/co/.<fE/OTT/CURB )NLE1/^PIPE 14A^(0nP?^As/^<PIPE 8A5W5^"1.8411c "V/^BASIN2.^1 ac/^^ROOfDRAiPIPE/^>//yuDRAINAGE BASINFUTURE PHASE1A/£/5.00PIPE 10A^/ac/mi ii^Hu:^ n/^^f//'Py~0^.4a1 s'u^—^u [ !^; uPIPE 11A^,^y/<^s\•^y^^DETENTIO^s^ASINBASIN^flA2,00 aiBA9AnE/^^!a/%/^ t^a/-ROOFPlOAlU<PIPE^t^>k^srBASIN 2B 0.33 acPIPE 5BDAGIN 3D 0.40 ac\PIPE1BL^1sa:36-@PIPE 9Bae:V)' ^ 15'?^»Jk "^PIPE 8B-PIPE 78PIPE 4BPIPE2BPIPE 3BPIPE 6BDRAINAGE BASIN 1BPHASE 2-3 37.19ac050100200IN FEETSTAHLYI0)Ill0(0S s.h^lI.o80za•52iSl^s"igi!]ilfisiuItsz0sUJ 0-^(0lm. jQF:B«SIS^ l'?$3g|IJ!st§CDIsli81IsiBIIs2IrO&\-xsJ,^CNllII.!E^^li^-l^ls^|||S< z 5 zsillw F I ui1^8£8 £^CDPRBRlESIGNEO-IRAWN•HFI-KFn CDP,ATE 12/6/13SHEET^FIGURE 1^
0F)0Table 5Phase 1 Inlet Basin and Pipe Capacity Calculations2/6/2014Inlet Basin1A2A3A4A5A6A7A8A9A10A11A1B2B3BLand UseREMUREMUREMUREMUREMUREMUREMUREMUREMUREMUREMUREMUREMUREMUDrainage Area (acres)5.000.320.791.031.842.110.520.691.832.090.4937.190.330.46Slope (%)2.12.12.12.12.12.12.12.12.12.12.12.12.12.1Runoff Coefficients0.60.60.60.60.60.60.60.60.60.60.60.60.60.6Frequency Adjustment Factor, Cf1.11.11.11.11.11.11.11.11.11.11.11.11.11.1Basin Length (ft)575180307410357377263581387439340423287425Time of Concentration (min)15.48.611.313.012.112.510.415.512.613.511.813.210.913.2Peak Flow CalculationsDesign Storm25yr25yr25yr25yr25yr25yr25yr25yr25yr25yr25yr25yr25yr25yrIntensity at Tc (Figure 1-2 pg. 29) (in/hr)1.862.702.282.072.172.132.391.862.112.032.202.052.332.05Peak Runoff Rate at Tc (Q = CIA) (cfs)5.580.521.071.282.392.700.750.762,322.550.6445.840.470.56Phase 1 Pipe CapacityPlan Pipe NumberDetention Basin A Pipe NetworkPipe Number1A2A3A4A5A6A7A8A9A10A11A12A13A14A15A16APipe Size (in)30.0018.0027.0015.0027.0027.0018.0015.0015.0018.0015.0015.0015.0015.0015.0015.00Manning's "n" (PVC)0.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.0130.013|Area (ft2)4.911.773.981.233.983.981.771.231.231.771.231.231.231.231.231.23'Wetted Perimeter (ft)7.854.717.073.937.077.074.713.933.934.713.933.933.933.933.933.93Hydraulic Radius (ft)0.630.380.560.310.560.560.380.310.310.380.310.310.310.310.310.31Slope (ft/ft)0.00270.01000.00270.01000.00270.00270.01000.00500.00500.01000.00500.00500.01000.01000.00500.0050Full Flow Capacity (cfs)21.3710.5316.146.4816.1416.1410.534.584.5810.534.584.584.586.486.484.583.735.285.283.733.7311AN13A14ANONE16ANONE15A2.161.400.640.76K7@"Velocity (ft/sec)4.355.964.065.284.064.065.963.733.735.963.73Contributing Inlet BasinContributing PipesNONE2A1ANONENONE4A2ANONE3A6A4A7ANONE8A5ANONEj^b«^ yiasaR]NONE11ANONE3A5A12A9A10Aa^^:™a|^^pBini^^.an^^aNNBilSyHBBBIiIsEJiSN^^:^r''::':8a^i^% CapacityDetention Basin B Pipe Network96%53%93%8%90%83%95%52%59%46%56%47%22%10%T7%~^17%-Pipe Number1B2B3B4B5B6B7BSB9BPipe Size (in)Manning's "n" (PVC)36.000.01336.000.01330.000.01330.000.01312.000.01330.000.01324.000.01315.000.01312.000.013Area (ft')Wetted Perimeter (ft)7.079.427.079.424.917.854.917.850.793.144.917.853.146.281.233.930.793.14Hydraulic Radius (ft)Slope (ft/ft)0.750.0060Full Flow Capacity (cfs)0.750.00600.630.00450.630.00450.250.00500.630.00450.500.01000.310.00450.250.005051.8051.807.337.332B3B27.59IVelocity (ft/sec:IContritsuflng5.6227.595.622.533.2227.595.6222.687.224.353.542.533.22NONEContributing Pipes4BNONE6B2BNONENONE8B1BNONENONE10B3BNONE5BFlow Contribution from Phase 2-3 (cfs)[ACRBr FTp@ FI8W(er$7'"W.VT"'25.84AG.srZT.037B^1.U3u.4 y9BZU.OD% Capacity-90%-90%76%76%18%75%20.00V6SS\~88%-NN^^KIaB^6^?'—?<«^^l13%22%
00Table 6Phase 1 Detention Basin CalculationsTime of Concentration Calculations Preconstructlon Postconstruction Storm Sewer FlowLand Use Open Land REMU REMUDrainage Area (acres) 16.70 16.70 16.70Slope (%) 2.1 2.1 2.1Runoff Coefficients 0.2 0.6 0.6Frequency Adjustment Factor, Cf 1 1 1.1Basin Length (ft) 1650 423 423Time of Concentration (min) 53.4 15.0 13.2Peak Flow CalculationsDesign Storm 10-Year 10-Year 25-YearIntensity at Tc (Figure 1-2 pg. 29) (in/hr) 0.69 1.57 2.05Peak Runoff Rate at Tc(Q=CIA)(cfs) 2.31 15.78 20.68(max release rate)Basin length based on typical Inlet areaRequired Storage VolumeStorm Durationf minutes)Intensity(in/hr)Future Runoff Rate(Q = CIA) (cfs)Runoff Volume(cf)Release Volume(cf)^4AXVOL.14788.10Required StorageNotes246810121416182024262830323436384042444648505254565860626466687072747678so82848688go929496981001021041061081101121141161181205.843.722.862.372.051.821.651.511.401.311.161.101.051.000.960.930.890.860.830.810.780.760.740.720.700.690.670.650.640.630.610.600.590.580.570.560.550.540.530.520.510.510.500.490.480.480.470.470.460.450.450.440.440.430.430.420.420.410.4158.5037.2828.6423.7620.5518.2516.5115.1414.0313.1011.6311.0410.5210.06g.659.288.948.638.358.097.857.627.417.227.046.876.716.566.416.28e.156.035.915.805.705.605.505.415.325.235.155.075.004.934.864.794.724.664.604.544.494.434.384.324.274.234.184.134.097020.338947.8410312.1711404.5712330.9713143.4913872.1014535.8115147.5615716.5716752.1717228.1217680.8318112.9718526.7718924.0819306.4818675.3120031.7220376.7320711.2221035.9721351.6621658.9221958.2922250.2622535.2922813.7723086.0823352.5523613.4923869.1924119.8924365.8524607.2824844.3825077.3725306.4025531.6425753.2525971.3826186.1526397.7126606.1626811.6227014.1927213.9927411.1027605.6027797.6027987.1728174.3828359.3028542.0228722.5928901.0729077.5329252.0329424.61^76.75553.49830.24iioe.gg1383.741660.481937.232213.982490.722767.473320.973597.713874.464151.214427.964704.704981.455258.205534.945811.696088.446365.196641.936818.687195.437472.177748.928025.678302.428579.168855.919132.669409.409686.159962.9010239.6510516.3910793.1411069.8911346.6311623.3811900.1312176.8812453.6212730.3713007.1213283.8713560.6113837.3814114.1114390.8514667.6014944.3515221.1015497.8415774.5916051.3416328.0816604.83t)/43.598394.359481.9310297.5810947.2311483.0111934.8712321.8312656.8312948.1013431.2113630.4113806.3713961.7614098.8214219.3814325.0314417.1114496.7814565.0414622.7814670.7814709.7314740.2414762.8614778.0914786.3614788.1014783.6614773.3914757.5S14736.5314710.4914679.7014644.3814604.7514560.8814513.2614461.7514406.6214348.0014286.0214220.8314152.5314081.2514007.0813930.1213850.481376S.2413683.4913596.3113506.7S13414.9613320.9213224.7513126.4813026.2012923.9412819.78Required Storage
n0Table 7Phase 2 and 3 Detention Basin CalculationsTime of Concentration Calculations Preconstmction Postconstructlon Storm Sewer FlowLand Use-Drainage Area (acres)Slope (%)Runoff CoefficientsFrequency Adjustment Factor, CfBasin Length (ft)Time of Concentration (min)Peak Flow CalculationsDesign StormIntensity at Tc (Figure 1-2 pg. 29) (in/hr)Peak Runoff Rate at Tc (Q = CIA) (cfs)Open Land37.982.10.21262067.3REMU37.982.10.6142315.010-Year 10-Year0.59 1.574.51 35.BS(max release rate)REMU37.982.10.61.142313.225-Year2.0546.8fBasin length based on typical inlet areaRequired Storage VolumeStorm Duration(minutes)Intensity(in/hrtFuture Runoff Rate(Q = CIA) (cfs)Runoff Volume(cf)Release Volume(cf)MAX VOL.36466.56Required Storage(cf)Notes2468101214161820242628303234363840424446485052545658606264666870727476788082848688go929496981001021041061081101121141161181205.843.722.862.372.051.821.651.511.401.311.161.101.051.000.960.930.890.860.830.810.780.760.740.720.700.690.670.650.640.630.610.600.590.580.570.560.550.540.530.520.510.510.500.490.480.480.470.470.460.450.450.440.440.430.430.420.420.410.41133.0584.7965.1554.0446.7441.5237.5634.4431.9029.7926.4625.1223.9322.8921,9521.1020.3319.6318.9818.3917.8417.3316.8616.4216.0115.6215.2514.9114.5814.28is.gg13.7113.4413.1912.9512.7312.5112.3012.1011.9011.7211.5411.3711.2111.0510.8910.7510.6010.4610.3310.2010.079.959.849.729.619.509.409.2915966.0020349.6423452.4825936.8528043.7329891.6031548.6333058.0934449.3635743.4338098.6639181.0840210.6541193.4542134.5443038.1343907.7944746.6045557.1746341.8147102.5247841.0848559.0549257.S349938.6650602.6951250.9151884.2552503.5553109.5853703.0254284.5454854.7055414.0755963.1556502.3957032.2557553.1258065.3858569.3859065.4559553.9060035.0260509.0960976.3661437.0761891.4562339.7262782.0963218.7463649.8564075.6264496.1964911.7365322.3965728.3166129.6266526.4766918.86541.571083.141624.722166.292707.863249.433791.004332.574874.155415.726498.867040.437582.018123.588665.159206.729748.2910289.8610831.4411373.0111914.5812456.1512997.7213539.3014080.8714622.4415164.0115705.5816247.1616788.7317330.3017871.8718413.4418955.0119496.5920038.1620579.7321121.3021662.8722204.4522746.0223287.5923829.1624370.7324912.3025453.S825995.4526537.0227078.5827620.1628161.7428703.3129244.8829786.4530328.0230869.5931411.1731952.7432494.3115424.4319266.5021827.7623770.5625335.8726642.1727757.6328725.5129575.2130327.7131599.8032140.6532628.6433069.8733469.3933831.4134159.5034456.7334725.7334968.8035187.9435384.9335561.3335718.5335857.8035980.2536086.9036178.6736256.4036320.8536372.7236412.6636441.2636459.0636466.5636464.2436452.5236431.8236402.5036364.9336319.4336266.3136205.8636138.3636064.0535983.1935896.0035802.7035703.4935598.5735488.1235372.3135251.3135125.2834994.3734858.7134718.4634573.7334424.65Required Storage