HomeMy WebLinkAbout17 - Design Report - The Ridge LLC - Stormwaterr\"\DESIGN REPORTSTORMWATER MANAGEMENTTHE RIDGE, LLCPrepared for:The Ridge, LLC4325 Fallen Street, Bozeman, MT 59718Prepared by:C&H Engineering and Surveying, Inc.1091 Stoneridge Drive, Bozeman, MT 59718(406)587-1115Project Number: 16981September 2017
nnINTRODUCTIONThe proposed Ridge, LLC modifications will extend The Ridge, LLC parking lot west to RavalliStreet/Fallon Street intersection. Stormwater mnofffrom the project will be conveyed via surfaceflow in catch curb and gutter to three proposed storm sewer curb inlet. The proposed inlets flowto a proposed retention pond to the north of the proposed parking lot. A drainage area map inincluded in Appendix A. Calculations for the contributing drainage areas (total area, weighted Cfactor, and time of concentration) are included in Appendix B-D.STORM SEWER FACILITIES DESIGNStorm sewer facilities were sized for the 25-yr storm using Manning's Equation. For each inlet,the contributing area, weighted C factor, and time to concentration were calculated (see AppendixB). These values were input into Manning's Equation to check capacity and flow characteristicsfor inlets and storm drain pipes. The Storm Sewer Summary Report is included in Appendix C.RETENTION POND DESIGNPonds have been sized according to City ofBozeman Design Standards. Retention ponds are sizedto capture the entire volume of the 10-year, 2-hour storm event.Retention Pond #1Retention Pond #1 is located just north of the proposed parking lot. It receives runoff fromDrainage Areas 1, 2 and 3, totaling 3.23 acres. Runofffrom Drainage Area 1 is captured in theproposed storm inlet 1, located southwest of the Lot 9. From this point, the mnoffwill flow intoan 12" PVC pipe that will convey mnoffto stonn inlet 1A, located south of Lot 9. RunofffromDrainage Area 2 will also be captured in the proposed storm inlet 1A. From this point, the mnoffwill flow into a 15" PVC pipe that will convey the mnoffto storm inlet 1B, located southwest ofthe proposed retention pond. Runoff from Drainage Area 3 will also be captured in the proposedstorm inlet IB. From this point, the runoffwill flow into an 18" PVC pipe that will convey therunoffto the proposed retention pond. The required pond volume was calculated to be 5,132 cubicfeet. The proposed pond is designed to store 5,800 cubic feet of water. In the case of larger stormsbeyond the pond's capacity to capture and infiltrate, the pond will overtop and flow north into anoverflow swale that will convey the water to the existing retention pond. Supporting calculationsfor the required pond volume can be found in Appendix D.
nnOffsite FlowDrainage Area #EX flows to the existing curb cut on the northwest side of the existing Ridgeparking lot. This stormwater currently drains to the existing retention pond #1 to the northwest ofthe existing Ridge parking lot. The proposed changes to this drainage area include removing16,484 square feet of landscape and replacing it with 15,938 square feet ofhardscape, and 2,950square feet of landscape. The additional required capacity of the pond to accommodate thisdecrease in landscape area was calculated to be 843 cubic feet. In order to provide adequate pondvolume to store this increase in runoff, the existing retention pond will be expanded to the southto add 1,030 cubic feet of storage. See appendix D for supporting calculations.Drainage Area #EX 2 flows to the existing retention pond #3 in the southwest comer of the RavalliSt/Ferguson Ave intersection. This pond was originally sized in 2006, with a contributing area of1.57 acres. Originally, the amount of hardscape roof area was underestimated for futuredevelopment, so the pond was resized to accommodate this increased roof area. The original pondvolume was calculated to be 2,121 cubic feet. With the increased hardscape area, the pond volumewas calculated to be 2,669 cubic feet. The pond was originally installed with a volume of 8,125cubic feet and therefore will have adequate capacity to hold the additional runoff.
nnAPPENDIX ADRAINAGE AREA MAP
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nnAPPENDIX BDRAINAGE AREA CALULATIONS
0nDrainage Area #11. Calculate Area and Weighted C Factor/\rea C *Contributing Area C (ft2) AreaROWHardscape 0.95 7339 6972ROW Landscape 0.2 6475 1295OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0Commercial Neighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres)C = Weighted C Factor1381482670.31710.602. Calculate Tc (Time to Concentration)Tc Overland FlowTc=1.87(1.1-CCf)D1/2/S1/3S = Slope of Basin (%)C = Rational Method RunoffCoefficientCf= Frequency Adjustment FactorD = Length of Basin (ft)Tc Overland Flow (minutes)Tc Gutter FlowTc = L/V/60V=(1.486/n)R2raS1/2n = Mannings CoefficientR = Hydraulic Radius A/P (ft)S = slope (%)L = length of gutter (ft)V = mean velocity (ft/s)Tc Gutter Flow (minutes) =Tc Total =2.350.951.177.921.24StormReturn(yrs)2 to 1011 to 2526 to 5051 to 100Cf11.11.21.25r0.0130.131.64%0(0.15' below top ofcurb)fe 3.84ffi» 0.00r 1^43. Calculate Flow (Rational Formula)
n0Q=CIAC = Weighted C Factorl=0.78Tc-064(in/hr)A = area (acres)Q = REQUIRED GUTTER CAPACITY (cfs)0.60 (calculated above)(25-yr9.33 storm)0.32 (calculated above)(assuming no carry1.77 flow)PROVIDED GUTTER CAPACITY1. Calculate Gutter Capacity @ 0.15'Below Top of CurbQ = (1.486/n)AR2ra S1/2n = Mannings CoefficientA = Area (ft2)P = Wetted perimeter (ft)R = Hydraulic Radius A/P (ft)S = slope (%)0.0131.249.230.131.64%(0.15'below top ofcurb)(0.15' below top ofcurb)(0.15'below top ofcurb)Q = PROVIDED GUTTER CAPACITY (cfs)B4.76 !
nnDrainage Area #21. Calculate Area and Weighted C FactorArea C *Contributing Area C (ft2) AreaROWHardscape 0.95 26785 25446ROW Landscape 0.2 7542 1508OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0Commercial Neighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres) 0.7880C = Weighted C Factor 0.792. Calculate Tc (Time to Concentration)Tc Overland FlowTc=1.87(1.1-CCf)D1/2/S1/3S = Slope of Basin (%)C = Rational Method RunoffCoefficientCf = Frequency Adjustment FactorD = Length of Basin (ft)Tc Overland Flow (minutes)Tc Gutter FlowTc = LA//60V = (1.486/n)R2/3 S1/2n = Mannings CoefficientR = Hydraulic Radius A/P (ft)S = slope (%)L = length of gutter (ft)V = mean velocity (ft/s)Tc Gutter Flow (minutes) =34327 2695^,2.110.711.183.54.240.0130.131.36%1203.500.57ri StormI Return(yrs)2 to 10j 11 to 2526 to 5051 to 100Cf11.11.21.25(0.15'below top ofcurb)
0nTc Total =3. Calculate Flow (Rational Formula)Q=CIAC = Weighted C Factorl=0.78Tc-064(in/hr)A = area (acres)Q = REQUIRED GUTTER CAPACITY (cfs)4.820.79 (calculated above)(25-yr3.92 storm)0.79 (calculated above)(assuming no carry2.42 flow)PROVIDED GUTTER CAPACITY1. Calculate Gutter Capacity @ 0.15'Below Top of CurbQ=(1.486/n)AR2/3S1/2n = Mannings CoefficientA = Area (ft2)P = Wetted perimeter (ft)R = Hydraulic Radius A/P (ft)S = slope (%)0.0131.249.230.131.36%(0.15'below top ofcurb)(0.15' below top ofcurb)(0.15' below top ofcurb)Q = PROVIDED GUTTER CAPACITY (cfs)"4.34^
nnDrainage Area #31. Calculate Area and Weighted C FactorArea C *Contributing Area C (ft2) AreaROWHardscape 0.95 29302 27837ROW Landscape 0.2 63381 12676OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0Commercial Neighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres) 2.1277C = Weighted C Factor 0.442. Calculate Tc (Time to Concentration)Tc Overland FlowTc=1.87(1.1-CCf)D1/2/S1/3S = Slope of Basin (%)C = Rational Method RunoffCoefficientCf = Frequency Adjustment FactorD = Length of Basin (ft)Tc Overland Flow (minutes)Tc Gutter FlowTc = LA//60V=(1.486/n)R2/3S1/2n = Mannings CoefficientR = Hydraulic Radius A/P (ft)S = slope (%)L = length of gutter (ft)V = mean velocity (ft/s)92683 405131.780.871.191.82.040.0130.131.16%203N 3.23StormReturn(yrs)2 to 1011 to 2526 to 5051 to 100Cf11.11.21.25(0.15' below top ofcurb)
n0Tc Gutter Flow (minutes) =Tc Total =1.053.093. Calculate Flow (Rational Formula)Q=CIAC = Weighted C Factorl=0.78Tc-064(in/hr)A = area (acres)Q = REQUIRED GUTTER CAPACITY (cfs)0.44 (calculated above)(25-yr5.21 storm)1.32 (calculated above)(assuming no carry3.00 flow)PROVIDED GUTTER CAPACITY1. Calculate Gutter Capacity @ 0.15'Below Top of CurbQ = (1.486/n)AR2/s S1/2n = Mannings CoefficientA = Area (ft2)P = Wetted perimeter (ft)R = Hydraulic Radius A/P (ft)S = slope (%)Q = PROVIDED GUTTER CAPACITY (cfs)0.0131.249.230.131.16%(0.15'below top ofcurb)(0.15' below top ofcurb)(0.15' below top ofcurb)4.00Note: Gutter capacity area was modified to include only contributing area to that stretch ofgutter, which was calculated to be 1.32 acres.
n0APPENDIX CSTORM SEWER FACILITIESCALCULATIONS
nnPipe #1REQUIRED CAPACITY1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 7339 6972ROW Landscape 0.2 6475 1295OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres)C = Weighted C Factor1381482670.31710.602. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)i = 0.78x-064 (25-yr Storm, Fig. 1-3, COB Design Standards)x = storm duration (hrs)/' = rainfall intensity (in./hr.)3. Calculate 25-yr Pond Outflow RateQ=CiAC = Rational Method RunoffCoefficienti = rainfall intensity(in./hr.)A = Area (acres)0.02 (DA #1)9.330.60 (calculated above)9.33 (calculated above)0.32 (calculated above)Q = 25-yr Pipe Flow Rate (cfs)•\.77
nnPipe #1AREQUIRED CAPACITY1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 34125 32418ROW Landscape 0.2 14016 2803OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres)C = Weighted C Factor48141352221.10520.732. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)i = 0.78x-064 (25-yr Storm, Fig. 1-3, COB Design Standards)x = storm duration (hrs)/ = rainfall intensity (in./hr.)3. Calculate 25-yrPond Outflow RateQ=CiAC = Rational Method RunoffCoefficienti = rainfall intensity(in./hr.)A = Area (acres)0.08 (DA #2)3.920.73 (calculated above)3.92 (calculated above)1.11 (calculated above)Q = 25-yr Pipe Flow Rate (cfs)3.17
nnPipe #1BREQUIRED CAPACITY1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 63427 60256ROW Landscape 0.2 35321 7064OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalA = Area (acres)C = Weighted C Factor98748 673202.26690.682. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)i = 0.78x-064 (25-yr Storm, Fig. 1-3, COB Design Standards)x = storm duration (hrs)/ = rainfall intensity (in./hr.)3. Calculate 25-yr Pond Outflow RateQ=CiAC = Rational Method RunoffCoefficienti = rainfall intensity(in./hr.)A = Area (acres)0.08 (DA #2)3.920.68 (calculated above)3.92 (calculated above)2.27 (calculated above)Q = 25-yr Pipe Flow Rate (cfs)6.05
nnAPPENDIX DPOND SIZING CALCULATIONS
nnRetention Pond #1REQUIRED VOLUME1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 63427 60256ROW Landscape 0.2 77397 15479OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalC=Weighted C Factor 0.542. Calculate Required VolumeQ=CIAV=7200QC = Weighted C Factor 0.54I = intensity (in/hr) 0.41A = Area (acres) 3.23Q = runoff (cfs) 0.71V = REQUIRED VOL (ft3) 5132140824 75735(10yr, 2hr storm)
nnRetention Pond #EX (Post-Construction)REQUIRED VOLUME1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaHardscape 0.95 15940 15143Landscape 0.2 2951 590OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalC=Weighted C Factor 0.832. Calculate Required VolumeQ=CIAV=7200QC = Weighted C Factor 0.83I = intensity (in/hr) 0.41A = Area (acres) 0.43Q = runoff (cfs) 0.15V = REQUIRED VOL (ft3) 10661889015733(10yr, 2hr storm)Note: This volume is the required volume from only the additional development, not the entiredrainage area.
nnRetention Pond #EX (Pre-Construction)REQUIRED VOLUME1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaHardscape 0.95 0 0Landscape 0.2 16484 3297OS/Park 0.2 0 0Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalC=Weighted C Factor 0.202. Calculate Required VolumeQ=CIAV=7200QC = Weighted C Factor 0.20I = intensity (in/hr) 0.41A = Area (acres) 0.38Q = runoff (cfs) 0.03V = REQUIRED VOL (ft3) 223164843297(10yr, 2hr storm)Note: This volume is the required volume from only the pre-developed landscape, not the entiredrainage area.
nnRetention Pond #EX 2 (Original Contributing Areas)REQUIRED VOLUME1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 23477 22303ROW Landscape 0.2 0 0OS/Park 0.2 44964 8993Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalC=Weighted C Factor 0.462. Calculate Required VolumeQ=CIAV=7200QC = Weighted C Factor 0.46I = intensity (in/hr) 0.41A = Area (acres) 1 .57Q = runoff (cfs) 0.29Existing Pond Volume = 8,125V = REQUIRED VOL (ft3) 2,1216844131296(10yr, 2hr storm)Note: This volume is the original design volume from 2006, which slightly underestimated thefuture hardscape (roof) area.
n0Retention Pond #EX 2 (New Contributing Areas)REQUIRED VOLUME1. Calculate Area and Weighted C Factorc*Contributing Area C Area (ft2) AreaROWHardscape 0.95 34265 32551ROW Landscape 0.2 0 0OS/Park 0.2 34176 6835Low-Med Residential 0.35 0 0Dense Residential 0.5 0 0CommercialNeighborhood 0.6 0 0Commercial Downtown 0.8 0 0Industrial 0.8 0 0TotalC=Weighted C Factor 0.582. Calculate Required VolumeQ=CIAV=7200QC = Weighted C Factor 0.58I = intensity (in/hr) 0.41A = Area (acres) 1 .57Q = runoff (cfs) 0.37Existing Pond Volume = 8,125V = REQUIRED VOL (ft3) 2,6696844139387(10yr, 2hr storm)
INSPECTION AND MAINTENANCE FORSTORMWATER MANAGEMENT FACILITIESThe Property Owners Association shall be responsible for the maintenance of the stormwaterdrainage facilities within the Ridge Athletic Club Campus.Storm Water Facilities:1. Drainage swales slope toward retention and detention ponds to collect storm waterrunoff and channel it to the retention or detention pond.2. Retention Ponds collect storm water runoffand store the water until it evaporates and/orinfiltrates into the ground.3. Detention ponds collect storm water runoff while allowing some water to drain toanother location.4. Culverts are pipes which channel storm water from ditches or swales under roads.5. Pipe Networks convey storm water to different discharge locations underground.6. Inlets are facilities where storm water mnoff enters a pipe network. Inlets include stormwater manholes and drains.7. Catch Basins are sumps typically located directly below storm water inlets and allowsediment to settle before storm water enters the pipe network.8. Outlets are points where storm water exits a pipe network.9. Drywells are underground storm water collection facilities that collect and temporarilystore runofffrom rooftops and landscaped areas before allowing storm water to infiltrateinto the ground.Post Construction Inspection:1. Observe drain time in retention ponds for a storm event after completion of the facility toconfirm that the desired drain time has been obtained. If excessively slow infiltrationrates are observed then excavate a minimum 5 ft by 5 ft drain to native gravels (or nativewell-draining material) and backfill with well-draining material (pit-run).2. Observe that drywells, catch basins, and outlet structures are clear of any material orobstructions in the drainage slots. Inspect these structures to insure proper drainagefollowing a storm event. Immediately identify and remove objects responsible forclogging if not draining properly.Semi-Annual Inspection:1. Check retention ponds and dry wells three days following a storm event exceeding '/4inch of precipitation. Failure for water to percolate within this time period indicatesclogging or poor-draining soils. Clear any clogs and replace any poor-draining soils withwell-draining gravely soils.2. Check for grass clippings, litter, and debris in drainage swales, catch basins, dry wells,culverts and retention ponds. Flush and/or vacuum drywells or storm water pipes ifexcessive material is observed in the facilities.Standard Maintenance:1. Remove sediment and oil/grease from retention ponds and detention2. Inspect and remove debris from drainage swales, catch basins, dry wells, and retentionponds. Use a vacuum truck to clean catch basins and dry wells.
3. Monitor health of vegetation and revegetate as necessary to maintain full vegetativecover.4. Inspect for the following issues: differential accumulation of sediment, drain time, signsof petroleum hydrocarbon contamination (odors, oil sheen in pond water), standing water,trash and debris.Sediment accumulation:In most cases, sediment from a retention pond does not contain toxins at levels posing ahazardous concern. However, sediments should be tested for toxicants in compliance withcurrent disposal requirements and if land uses in the drainage area include commercial orindustrial zones, or if visual or olfactory indications of pollution are noticed. Sedimentscontaining high levels of pollutants should be disposed of in accordance with applicableregulations and the potential sources of contamination should be investigated and contaminationpractices terminated.