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Home My WebLink About15 - Design Report - South University District Ph 1 & Stadium View Apartments Amended for Ph 1B - Stormwater Storm Water Plan South University District — Phase 1 , and Stadium View Apartments Amended for Phase 1 B December, 2015 Submitted to: City of Bozeman Engineering Department 20 East Olive Bozeman, MT 59715 Prepared by: Stahly Engineering and Associates 851 Bridger Drive, Suite 1 Bozeman, MT 59715 (406) 522-9526 ��IREEAf�c ISTAHLY1 ens 1970 4 s�C1 RT�%- Storm Water Plan Contents Description of Phase 1 B Amendments General Information Existing Conditions and General Design Criteria Storm Drainage Plan Description Estimation of Runoff Pre-development Runoff— Phase 1 Post-development Runoff— Phase 1 Pre-development Runoff— Phase 2-3 Post-development Runoff— Phase 2-3 Storage/Treatment Facilities Outfall Structure Weir Sizing Curb and Gutter Capacity Inlet Capacity Facilities Maintenance Figures and Tables Figure 1. Inlet Basin Exhibit Table 1. Runoff Calculations— Phase 1 Table 2. Runoff Calculations— Phases 2-3 Table 3. Outfall Structure Sizing Table 4 Curb and Gutter Capacity Calcs Table 5. Phase 1 Inlet Basin and Pipe Capacity Calculations Table 6. Phase 1 Detention Basin Calculations Table 7. Phase 2 and 3 Detention Basin Calculations Storm Water Plan 1 12/18/2015 Description of Phase 1 B Amendments The South University District - Phase 1 B is a subsequent minor subdivision of Lot 2, SUD Subdivision Phase 1. The subsequent division will provide right of way dedications for South 14th Avenue, State Street and Campus Boulevard and will result in a 3.66-acre lot, which will be the location of Phase 1 B. In 2014, the storm water infrastructure for SUD Phase 1 was constructed as part of the development of the Stadium View Apartments in Lot 1. This network of storm drains and the two detention basins is the backbone for the improvements to Phase 1 B, as originally intended. The previously submitted Storm Water Plan for the South University District Phase 1 subdivision accounted for the storm water that is contributed by the development of Phase 1 B. In the following report, Phase 1 B (referred to as Lot 2) was designated as an entire drainage basin (Drainage Basin 1A) in the runoff estimates. With the development of a grading plan for Phase 1 B, the drainage basin has been further divided into smaller basins to more accurately represent storm water flow. Based on the grading plan, a new pipe network (network C) will be constructed within phase 1 B. This network will discharge into Detention Basin A, as originally intended, but will have its own inlet into the basin, rather than a connection through pipe network A. The amendments updating the Storm Water Plan with improvements from Phase 1 B are as follows: - The Phase 1B drainage basin has been broken down into sub basins 1A.1 through 1A.8 as shown in the updated Inlet Basin Exhibit (Figure 1). - Updates have been made to Table 5 to include the sub basins 1A.1 through 1A.8, and the addition of pipe network C capacity calculations. General Information The South University District - Phase 1 subdivision is located within the City of Bozeman adjacent to South 11th Street and south of Kagy Boulevard. The subdivision is located west of Bobcat Stadium and is south of the existing Stadium 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 View Apartments, a 499-bed student housing facility which is currently under review. Storm drainage improvements include those required for public streets installed with the Phase 1 South University District subdivision as well at improvements serving the Stadium View student apartments located on Lot 1 of the subdivision. Storm drainage improvements also include backbone infrastructure serving future phases of development to the west and south. Storm Water Plan 2 12/18/2015 The developer's contact information is: Fountain Residential Partners 2626 Cole Ave, Suite 620 Dallas, TX 75204 Existing Conditions and General Design Criteria The existing condition at the site is undeveloped agricultural land. Down-gradient development has restricted storm drainage paths leaving the property to the north. An existing creek (Mandeville Creek) runs along the west edge of Phase 1 and is the only acceptable location for storm water to leave the site. Mandeville Creek continues to flow north through the City to the East Gallatin River. In accordance with the City of Bozeman Design Standards and Specifications Policy(COB Standards) an engineering analysis has been conducted for the South University District (SUD) property to limit post-development runoff to pre- development rates. Storm runoff originating on the site will be detained on-site and 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 the site. Inlets and storm sewers are sized to pass the 25-year event without overtopping roadways. Should a larger event overtop the roadways grading will divert storm water away from structures. Storm Drainage Plan The overall storm drainage plan for SUD — Phase 1 and Stadium View is depicted on Figure 1 at the end of this report. Overall drainage direction on the proposed development is indicated by arrows showing the proposed drainage patterns and inlet locations. Estimation of Runoff Runoff estimates are provided separately for Phase 1 (Lots 1 and 2) and Phases 2 and 3 located south of Phase 1 on Lot 3. Phase 1 is 16.7 acres. Phases 2 and 3 combined are 37.98 acres. The rational method was used to estimate peak flow rates and volumes from storm runoff. Standard assumptions in using the rational method include that rainfall 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 of concentration, and the runoff coefficient for a watershed is constant for similar Storm Water Plan 3 12/18/2015 land 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 1 A runoff coefficient of 0.20 for open land was selected for pre-development conditions. An average overland slope of 2.1% over a basin length of 1,650 feet provides a time of concentration of 53.4 minutes. The Bozeman IDF curves show a rainfall intensity for the 1 0-year design storm event of 0.69 in/hr. Applying this over the 16.7 acre site produces a runoff flow rate of 2.31 cfs at the downstream end of the basin. Post-development Runoff- Phase 1 Post-construction runoff was calculated using a runoff coefficient of 0.60 (commercial neighborhood) to account for future site development in accordance with 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 runoff from this lot (using commercial neighborhood inputs) was accounted for in the design and runoff calculations. The increased impervious area reduces the time of concentration to 15.0 minutes. The Bozeman IDP curves show a 1 0-year storm intensity of 1.57 in/hr. The rational method provides a 10-year peak runoff rate of 15.78 cfs. The same analysis for a 25-year event provides a peak runoff rate of 20.58 cfs. Table 1 Runoff Calculations - Phase 1 Pre-development Post-Development Post-Development Open Land Commercial Commercial Land Use Neighborhood Neighborhood Drainage Area (acres) 16.7 16.7 16.7 Slope(%) 2.1 2.1 2.1 Overland Runoff Coefficients 0.2 0.6 0.6 Frequency Adjustment Factor, Cf 1 1 1.1 Design Storm Frequency 10-vear 1 0-year 25-year Basin Length (ft) 1,650 423 423 Time of Concentration, Tc(min) 53.4 15.0 13.2 Intensity at Tc (Figure 1-2 pg. 29)(in/h ) 0.69 1.57 2.05 Runoff Rate(cfs) 1 2.31 15.78 20.58 In addition to the overall storm runoff calculations for Phase 1, the 25-year storm runoff flow rate for each storm drainage inlet basin has been determined based on the drainage plan shown on Figure 1. These calculations are provided in Table 5 at the end of this report. Storm Water Plan 4 12/18/2015 Pre-development Runoff- Phase 2-3 The storm water detention pond serving future Phases 2 and 3 will also be constructed with SUD- Phase 1 and was therefore analyzed to size the basin needed for this future development. A runoff coefficient of 0.20 for open land was selected for pre-development conditions. An average overland slope of 2.1% over a basin length of 2,620 feet provides a time of concentration of 67.3 minutes. The Bozeman OF curves show a rainfall intensity for the 1 0-year design storm event of 0.59 in/hr. Applying this over the 37.98 acre Phase 2-3 site produces a runoff flow rate of 4.51 cfs at the downstream end of the basin. Post-development Runoff- Phase 2-3 Post-construction runoff was calculated using a runoff coefficient of 0.60 (commercial neighborhood) to account for future site development in Phases 2-3 in accordance with the master plan. The increased impervious area reduces the time of concentration to 15.0 minutes. The Bozeman IDP curves show a 1 0-year storm intensity of 1.57 in/hr. The rational method provides a 10-year peak runoff rate of 35.88 cfs. The same analysis for a 25-year event provides a peak runoff rate of 46.81 cfs. Table 2 Runoff Calculations - Phase 2-3 Pre-development Post-Development Post-Development Open Land Commercial Commercial Land Use Neighborhood Neighborhood Drainage Area (acres) 37.98 37.98 37.98 Slope(%) 2.1 2.1 2.1 Overland Runoff Coefficients 0.2 0.6 0.6 Frequency Adjustment Factor, Cf 1 1 1.1 Design Storm Frequency 10-year 10-vear 25-vear Basin Length (ft) 2,620 423 423 Time of Concentration, Tc(min) 67.3 15.0 13.2 Intensity at Tc (Figure 1-2 pg. 29)(in/hr) 0.59 1.57 2.05 Runoff Rate(cfs) 4.51 35.88 46.81 In addition to the overall storm runoff calculations for Phases 2 and 3, the 25- year storm runoff flow rate for each storm drainage inlet basin has been determined based on the drainage plan shown on Figure 1. These calculations are provided in Table 5 at the end of this report. Storage/Treatment Facilities Simple pond routing using the modified rational method is provided for Phase I and Phases 2 and 3 in Tables 6 and 7 at the end of the report. This spreadsheet shows a required storage of 14,788 cubic feet of runoff for the 10-year event for Storm Water Plan 5 12/18/2015 Phase 1 and 36,467 cubic feet for Phases 2-3. The required storage is provided by 2 basins, one for the Phase 1 runoff and one for the Phase 2-3 runoff. The Phase 1 pond has a bottom area of 9075 square feet and 4:1 side slopes. The bottom elevation is 4928.00 and surface overflow to the west is provided at an elevation of 4930.50. The maximum depth is 1.5 feet, with a total volume of approximately 16,344 cubic feet. The pond for the future Phases 2-3 development has a bottom area of 23,105 square feet and 4:1 side slopes. The bottom elevation is 4931.5 and the surface overflow to the west is provided at an elevation of 4934.00. The maximum depth is 1.5 feet, with a total volume of approximately 36,500 cubic feet at this depth. The detention basins are located at the northwest (down-gradient) end of the site and will be vegetated with grass. Outfall Structure Weir Sizing The detention basin outflow for both the Phase 1 and the Phase 2-3 development is 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 COB Standards, the slot width of both weir structures was determined. The slot width for the Phase 1 pond discharge structure is 5 inches and the slot width for the Phase 2-3 discharge structure is 9 inches. These slot widths limit the discharge from the structure to pre-developed rates at the maximum depth of 1.5 feet. Table 3 Outfall Structure Weir Sizin Phase 1 Pre-developed Runoff cfs 2.31 Weir Coefficient"C" 3.33 Head ft 1.5 Slot Width in 5 Phase 2-3 Pre-developed Runoff Q 4.51 Weir Coefficient"C" 3.33 Head ft 1.5 Slot Width 9 In the occurrence of an event greater than the 10-year event the ponds are sized for, the overflow of the ponds directs flow to the west to Mandeville Creek. Curb and Gutter Capacity Storm runoff will be collected in street and parking lot curb and gutters. The hydraulic capacity of the curb and gutter was analyzed to determine if the curb would be overtopped in a 25-year event. The maximum 25-year event for any of the curb inlet basins produces approximately 2.70 cfs of runoff. The capacity of the curb at the lowest designed slope of 1.2% is 7.80 cfs at a depth of .15 feet below the top of the curb. Therefore, curb capacities in the development are adequate to carry the 25-year event. Storm Water Plan 6 12/18/2015 Table 4 Curb and Gutter Capacity Calcs Right-side slope X:1 0.05 Left-side slope X:1 33.00 Channel bottom width ft 0 Flow Depth ft 0.350 Flow Area ft"2 2.024 Wetted Perimeter ft 11.906 Width 0.035 Hydraulic Radius ft 0.170 Mannin 's Roughness 0.013 Slope ft/ft 0.012 Average Velocity ft/sec 3.85 Flow ft^3/sec 7.80 Inlet Capacity The curb inlets on the roadways in the development were analyzed to ensure they have capacity to accept flows conveyed to them without reaching a point 0.15 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 of curb). This capacity will convey the necessary flows. Facilities Maintenance The proposed storm drainage facilities will be operated and maintained by the property owner. The owner is responsible for quarterly maintenance of all storm water facilities. The maintenance includes, but is not limited to, visual inspection and removal of sediment from curbs, inlets, detention basins, and outlet structures as well as any necessary repairs to the facilities. Storm Water Plan 7 12/18/2015 Table 5 Phase 1 Inlet Basin and Pipe Capacity Calculations Inlet Drainage Basin Inlet Basin 1A.1 1A.2 1A.3 1A.4 1A.5 1A.6 1A.7 1A.8 2A 3A 4A 5A 6A 7A 8A 9A 10A 11A 1 113 2B 313 4B Land Use REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU Drainage Area acres 0.55 0.17 1.14 0.26 1.35 0.22 0.83 0.54 0.32 0.79 1.03 1.84 2.11 0.52 0.69 1.83 2.09 0.49 36.87 0.33 0.46 0.32 Slope % 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Runoff Coefficients 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Frequency Adjustment Factor,Cf 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Basin Length ft 610 175 610 175 280 150 300 140 180 307 410 357 377 263 581 387 439 340 423 287 425 275 Time of Concentration min 15.9 8.5 15.9 8.5 10.8 1 7.9 11.1 7.6 8.6 11.3 13.0 12.1 12.5 10.4L25 12.6 13.5 11.8 13.2 10.9 13.2 10.7 Peak Flow Calculations Design Storm 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 r 25 25 r 25 r 25 r 25 r 25 r 25 r 25 r Intensit at Tc Fi ure 1-2 .29 in/hr 1.83 2.72 1.83 2.72 2.34 2.86 2.29 2.93 2.70 2.28 2.07 2.17 2.13 2.39 2.11 2.03 2.20 2.05 2.33 2.05 2.36 Peak Runoff Rate at Tc(Q=CIA)(cfs 0.60 0.28 1.25 0.43 1.90 6.38 1.14 0.95 0.52 1.07 1.28 2.39 2.70 0.75 2.32 2.55 0.64 45.44 0.47 0.56 0.45 Detention Basin A-Pipe Network A Capacity Pipe Number 1A 2A 17A 3A 4A 5A 18A 6A 19A 7A 8A 9A 10A 11A 12A 13A 14A 15A 16A Pipe Size in 30.00 18.00 12.00 30.00 15.00 30.00 12.00 30.00 12.00 18.00 15.00 15.00 18.00 15.00 15.00 15.00 15.00 15.00 15.00 Mannin 's"n" PVC 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 Area ft2 4.91 1.77 0.79 4.91 1.23 4.91 0.79 4.91 0.79 1.77 1.23 1.23 1.77 1.23 1.23 1.23 1.23 1.23 1.23 Wetted Perimeter ft 7.85 4.71 3.14 7.85 3.93 7.85 3.14 7.85 3.14 4.71 3.93 3.93 4.71 3.93 3.93 3.93 3.93 3.93 3.93 Hydraulic Radius ft 0.63 0.38 0.25 0.63 0.31 0.63 0.25 0.63 0.25 0.38 0.31 0.31 0.38 0.31 0.31 0.31 0.31 0.31 0.31 Slope ft/ft 0.0027 0.0050 0.0050 0.0027 0.0100 0.0027 0.0050 0.0027 0.0050 0.0100 0.0050 0.0050 0.0100 0.0050 0.0050 0.0100 0.0100 0.0050 0.0050 Full Flow Capacity cfs 21.37 7.45 2.53 21.37 6.48 21.37 2.53 21.37 2.53 10.53 4.58 4.58 10.53 4.58 4.58 6.48 6.48 1 4.58 4.58 Velocity ft/sec 4.35 4.21 3.22 4.35 5.28 4.35 3.22 4.35 3.22 5.96 3.73 3.73 5.96 3.73 3.73 5.28 5.28 3.73 3.73 Mt ibutih Inlet Basin NONE 1A.1&1A.2 1A.3&1A.4 NONE 2A 112 of 3A 1/2 of 3A 1/2 of 4A 112 of 4A NONE 5A 6A 9A 10A NONE 7A 11A NONE 8A - Contributing Pipes 2A 17A NONE 4A NONE 6A None 7A None 8A NONE NONE 11A NONE 13A 14A NONE 16A NONE 3A 5A 18A 12A 9A 15A 19A 10A Actual Pipe Flow(cfs) 17.55 2.56 1.67 15.00 0.52 14.48 0.54 13.41 0.64 9.97 2.39 2.70 4.87 2.55 2.16 1-4 07-F 0. 44 0.76 0.76 %Capacity 82% 347/6 66% 70% 8% 68% 21% 63% 25% 95% 52% 59% 46% 56% 47% 22% 10% 17% 17% Detention Basin B-Pipe Network B Capacity Pie Number 1B 1 213 10B 11B 12B 313 13B 4B 513 613 7B 8B 913 Pipe Size in 36.00 36.00 12.00 12.00 24.00 30.00 24.00 30.00 12.00 30.00 24.00 15.00 12.00 Mannin 's"n" PVC 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 Area ft2 7.07 7.07 0.79 0.79 3.14 4.91 3.14 4.91 0.79 4.91 3.14 1.23 0.79 Wetted Perimeter ft 9.42 9.42 3.14 3.14 6.28 7.85 6.28 7.85 3.14 7.85 6.28 3.93 3.14 Hydraulic Radius ft 0.75 0.75 0.25 0.25 0.50 0.63 0.50 0.63 0.25 0.63 0.50 0.31 0.25 Slope ft/ft 0.0060 0.0060 0.0100 0.0100 0.0100 0.0045 0.0100 0.0045 0.0050 0.0045 0.0100 0.0045 0.0050 Full Flow Capacity cfs 51.80 51.80 3.57 3.57 22.68 27.59 22.68 27.59 2.53 27.59 22.68 4.35 2.53 Velocity f/sec 7.33 7.33 4.55 4.55 7.22 5.62 7.22 5.62 3.22 5.62 7.22 3.54 3.22 Contributing Inlet Basin NE 46 1121 113 NONE 1B NONE 26 NONE 1B NONE 3B Contributing Pipes 2B 3B NONE NONE NONE 4B NONE 5B NONE 713 NONE 913 NONE 10B 13B 68 8B 11B 12B Flow Contribution from Phase 2-3 cfs 1.00 21.72 1 1.00 21.72 Actual Pipe Flow cfs 46.92 1 46.92 0.45 1.00 21.72 23.75 1 1.00 22.75 0.47 22.28 1 21.72 10.56 0.56 %Capacity 91% 91% 13% 28% 96% 86% 4% 82% 18% 81% 96% 13% 22% Detention Basin 1A-Pipe Network C Capacity Pie Number 1C 2C 3C 4C 5C Pipe Size in 15.00 15.00 12.00 15.00 15.00 Mannin 's"n" PVC 0.013 0.013 0.013 0.013 0.013 Area ftZ 1.23 1.23 0.79 1.23 1.23 Wetted Perimeter ft 3.93 3.93 3.14 3.93 3.93 Hydraulic Radius ft 0.31 0.31 0.25 0.31 0.31 Slope fUft 0.0183 0.0150 0.0050 0.0050 0.0050 Full Flow Capacity cfs 8.76 7.93 2.53 4.58 4.58 Velocity ft/sec 7.14 6.46 3.22 3.73 3.73 Contributing Inlet Basin 1A.5 1A.7 1A.6 NONE 1A.8 Contributing Pipes 2C 3C NONE 5C NONE 4C Actual Pipe Flow cfs) 4.37 2.47 0.38 0.95 0.95 %Capacity 50% 31% 15% 21% 21% Table 6 Phase 1 Detention Basin Calculations Time of Concentration Calculations Preconstruction Postconstruction Storm Sewer Flow Land Use Open Land REMU REMU Drainage Area(acres) 16.70 16.70 16.70 Slope 1%) 2.1 2.1 2.1 Runoff Coefficients 0.2 0.6 0.6 Frequency Adjustment Factor,Cf 1 1 1.1 Basin Length(ft) 1660 423 423 Basin length based on typical inlet area Time of Concentration(min) 53.4 15.0 13.2 Peak Flow Calculations Design Storm 10-Year 10-Year 25-Year Intensity at Tc (Figure 1-2 pg.29)(in/hr) 0.69 1.57 2.05 Peak Runoff Rate at Tc(Q=CIA)(cfs) 2.31 15.78 20.58 (max release rate) Required Storage Volume MAX VOL. 14788,10 Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage Notes (minutes) (in/hr) (Q=CIA)(cfs) (cf) (cf) (cf) 2 5.84 58.50 7020.33 276.75 6743.59 4 3.72 37.28 8947.84 553.49 8394.35 6 2.86 28.64 10312.17 830.24 9481.93 8 2.37 23.76 11404.57 1106.99 10297.58 10 2.05 20.55 12330.97 1383.74 10947.23 12 1.82 18.25 13143.49 1660.48 11483.01 14 1.65 16.51 13872.10 1937.23 11934.87 16 1.51 15.14 14535.81 2213.98 12321.83 18 1.40 14.03 15147.56 2490.72 12656.83 20 1.31 13.10 15716.57 2767.47 12949.10 24 1.16 11.63 16752.17 3320.97 13431.21 26 1.10 11.04 17228.12 3597.71 13630.41 28 1.05 10.52 17680.83 3874.46 13806.37 30 1.00 10.06 18112.97 4151.21 13961.76 32 0.96 9.65 18526.77 4427.96 14098.82 34 0.93 9.28 18924.08 4704.70 14219.38 36 0.89 8.94 19306.48 4981.45 14325.03 38 0.86 8.63 19675.31 5258.20 14417.11 40 0.83 8.35 20031.72 5534.94 14496.78 42 0.81 8.09 20376.73 5811.69 14565.04 44 0.78 7.85 20711.22 6088.44 14622.78 46 0.76 7.62 21035.97 6365.19 14670.78 48 0.74 7.41 21351.66 6641.93 14709.73 50 0.72 7.22 21658.92 6918.68 14740.24 52 0.70 7.04 21958.29 7195.43 14762.86 54 0.69 6.87 22250.26 7472.17 14778.09 56 0.67 6.71 22535.29 7748.92 14786.36 58 0.65 6.56 22813.77 80M67 147$8.10, Required Storage 60 0.64 6.41 23086.08 8302.42 14783.66 62 0.63 6.28 23352.55 8579.16 14773,39 64 0.61 6.15 23613.49 8855.91 14757.58 66 0.60 6.03 23869.19 9132.66 14736.53 68 0.59 5.91 24119.89 9409.40 14710.49 70 0.58 5.80 24365.85 9686.15 14679.70 72 0.57 5.70 24607.28 9962.90 14644.38 74 0.56 5.60 24844.39 10239.65 14604.75 76 0.55 5.50 25077.37 10516.39 14560.98 78 0.54 5.41 25306.40 10793.14 14513.26 80 0.53 5.32 25531.64 11069.89 14461.75 82 0.52 5.23 25753.25 11346.63 14406.62 84 0.51 5.15 25971.38 11623.38 14348.00 86 0.51 5.07 26186.15 11900.13 14286,02 88 0.50 5.00 26397.71 12176.88 14220.83 90 0.49 4.93 26606.16 12453.62 14152.53 92 0.48 4.86 26811.62 12730.37 14081.25 94 0.48 4.79 27014.19 13007.12 14007.08 96 0.47 4.72 27213.99 13283.87 13930.12 98 0.47 4.66 27411.10 13560.61 13850.48 100 0.46 4.60 27605.60 13837.36 13768.24 102 0.45 4.54 27797.60 14114.11 13683.49 104 0.45 4.49 27987.17 14390.85 13596.31 106 0.44 4.43 28174.38 14667.60 13506.78 108 0.44 4.38 28359.30 14944.35 13414.96 110 0.43 4.32 28542.02 15221.10 13320.92 112 0.43 4.27 28722.59 15497.84 13224.75 114 0.42 4.23 28901.07 15774.59 13126.48 116 0.42 4.18 29077.53 16051.34 13026.20 118 0.41 4.13 29262.03 16328.08 12923,94 120 0.41 4.09 29424.61 16604.83 12819.78 Table 7 Phase 2 and 3 Detention Basin Calculations Time of Concentration Calculations Preconstruction Postconstruction storm Sewer Flow Land Use Open Land REMU REMU Drainage Area(acres) 37.98 37.98 37.98 Slope(%) 2.1 2.1 2.1 Runoff Coefficients 0.2 0.6 0.6 Frequency Adjustment Factor,Cf 1 1 1.1 Basin Length(ft) 2620 423 423 Basin length based on typical inlet area Time of Concentration(min) 67.3 15.0 13.2 Peak Flow Calculations Design Storm 10-Year 10-Year 25-Year Intensity at Tc (Figure 1-2 pg.29)(in/hr) 0.59 1.57 2.05 Peak Runoff Rate at Tc(Q=CIA)(cfs) 4.51 35.88 46.81 (max release rate) Required Storage Volume MAX VOL. 36466.56 Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage Notes (minutes) (In/hr) (Q=CIA)(cfs) (cf) (cf) (cf) 2 5.84 133.05 15966.00 541.57 15424.43 4 3.72 84.79 20349.64 1083.14 19266.50 6 2.86 65.15 23452.48 1624.72 21827.76 8 2.37 54.04 25936.85 2166.29 23770.56 10 2.05 46.74 28043.73 2707.86 25335.87 12 1.82 41.52 29891.60 3249.43 26642.17 14 1.65 37.56 31548.63 3791.00 27757.63 16 1.51 34.44 33058.09 4332.57 28725.51 18 1.40 31.90 34449.36 4874.15 29575.21 20 1.31 29.79 35743.43 5415.72 30327.71 24 1.16 26.46 38098.66 6498.86 31599.80 26 1.10 25.12 39181.08 7040.43 32140.65 28 1.05 23.93 40210.65 7582.01 32628.64 30 1.00 22.89 41193.45 8123.58 33069.87 32 0.96 21.95 42134.54 8665.15 33469.39 34 0.93 21.10 43038.13 9206.72 33831.41 36 0.89 2033 43907.79 9748.29 34159.50 38 0.66 19.63 44746.60 10289.86 34456.73 40 0.83 18.98 45557.17 10831.44 34725.73 42 0.81 18.39 46341.81 11373.01 34968.80 44 0.78 17.84 47102.52 11914.58 35187.94 46 0.76 17.33 47841.08 12456.15 35384.93 48 0.74 16.86 48559.05 12997.72 35561.33 50 0.72 16.42 49257.83 13539.30 35718.53 52 0.70 16.01 49938.66 14080.87 35857.80 54 0.69 15.62 50602.69 14622.44 35980.25 56 0.67 15.25 51250.91 15164.01 36086.90 58 0.65 14.91 51884,25 15705.58 36176.67 60 0.64 14.58 52503.55 16247.16 36256.40 62 0.63 14.28 53109.58 16788.73 36320.85 64 0.61 13.99 53703.02 17330.30 36372.72 66 0.60 13.71 54284.54 17871.87 36412.66 68 0.59 13.44 54854.70 18413.44 36441.26 70 0.58 13.19 55414.07 18955.01 36459.06 72 0.57 12.96 65963,15 19406$9; 36466.66, Required Storage 74 0.56 12.73 56502.39 20038.16 36464.24 76 0.55 12.51 57032.25 20579.73 36452.52 78 0.54 12.30 57553.12 21121.30 36431.82 80 0.53 12.10 58065.38 21662.87 36402.50 82 0.52 11.90 58569.38 22204.45 36364.93 84 0.51 11.72 59065.45 22746.02 36319.43 86 0.51 11.54 59553.90 23287.59 36266.31 88 0.50 11.37 60035.02 23829.16 36205.86 90 0.49 11.21 60509.09 24370.73 36138.36 92 0.48 11.05 60976.36 24912.30 36064.05 94 0.48 10.89 61437.07 25453.88 35983.19 96 0.47 10.75 61891.45 25995.45 35896.00 98 0.47 10.60 62339.72 26537.02 35802.70 100 0.46 10.46 62782.09 27078.59 35703.49 102 0.45 10.33 63218.74 27620.16 35598.57 104 0.45 10.20 63649.85 28161.74 35488.12 106 0.44 10.07 64075.62 28703.31 35372.31 108 0.44 9.95 64496.19 29244.88 35251.31 110 0.43 9.84 64911.73 29786.45 35125.28 112 0.43 9.72 65322.39 30328.02 34994.37 114 0.42 9.61 65728.31 30869.59 34858.71 116 0.42 9.50 66129.62 31411,17 34718.46 118 0.41 9.40 66526.47 31952.74 34573.73 120 0.41 9.29 66918.96 32494.31 34424.65 - i L. ♦�1NEE/jy _ I EST C STAHLY ,III 1970 Stadium Center Subdivision !L �9ffOfIHT� DETENTION BASIN A PIPE 1A PIPE 5A PIPE 6A N PIPE 4A PIPE 12A PIPE 15A W z w w w w , o� PIPE "'MM• w w w w w w w w w w II w w w w w w w w Milli! w w w w w w w w w TE STREET U BASIN 4A N L V�pp I I co1.03 ac ac PIPE 19A w w w w w I I Q N a E - PIPE 18A - PE 6A ca C ` rx 1 - - 1i VI �j >. 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PIPE 213 PIPE 3B PIPE 4B PIPE BB I 12B PIPE 6B O PIPE 7B W 2 N PIPE 11 B PIPE 13B W � H = W = O r- O DRAINAGE BASIN 113 N ? a co It m PHASE 2-3 36.87 ac CDP DESIGNED DRAWN CDP c I CHECKED CDP DATE 2/20/15 i z 0 50 100 200 SHEET IN FEET FIGURE 1