Loading...
HomeMy WebLinkAbout016_StormwaterEngineersReportBlock4Engineering Report Stormwater Design South University District Phase 3 – Block 4 Site Plan Submittal Updated May 2023 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 Stormwater Plan 1 5/12/2023 Engineering Report Table of Contents General Information and Design Criteria Existing Site Conditions Storm Drainage Plan Description Estimation of Runoff Sub Drainage Areas Inlet Capacity Retention Facilities Outfall Structure Weir Sizing Conveyance Capacity Curb and Gutter Facilities Maintenance Figures and Tables Figure 1. Vicinity Map Figure 2. Stormwater Plan Table 3. Curb and Gutter Conveyance Calculations Table 4. UPDATED - Runoff & Capacity Calc’s for SUD PHASE 2 (attached) Table 6. Runoff & Capacity Calc’s for SUD Block 4 – On-site (attached) Table 7. Runoff & Capacity Calc’s for SUD Block 4 – Off-site (attached) Appendix South University District Phase 2 Stormwater Engineering Report (attached) Stormwater Plan 2 5/12/2023 General Information and Design Criteria The intent of this report is to provide an updated to the SUD Phase 2 Subdivision infrastructure stormwater engineering report dated June 2017 and included as attachment to this report. This report will demonstrate conformance to the previously-designed, and partially-constructed stormwater infrastructure. The proposed South University District (SUD) Phase 3 Block 4 Development is located southwest of the intersection of South 11th Avenue and Student Drive. This development will consist of 243 residential units with 655 bedrooms on an 11.89-acre lot. Six different building types consisting of 20 unique unit configurations within the buildings is proposed with this development. The intent of this project is to create a variety of building types to create a diverse neighborhood in a growing part of town adjacent to the Montana State University Campus. Stormwater mitigation is achieved by using a compact, efficient stormwater management design utilizing Low Impact Design (LID) methodology to mitigate the impacts of stormwater runoff. The LID stormwater mitigation has been designed in accordance with City of Bozeman Design Standards and Specifications Policy for retention/infiltration facilities. Survivability of LID systems through conventional development is difficult. Erosion control Best Management Practices (BMP’s) will be utilized during construction to reduce the impacts of construction site runoff, until the LID systems are constructed. Plans are provided showing proposed grading, drainage flow paths, and stormwater retention/infiltration details and locations. The developer’s contact information is: Capstone Collegiate Communities Davis Maxwell 431 Office Park Drive Birmingham, AL 35223 Water supply and wastewater treatment will be provided by the City of Bozeman’s municipal systems. The system owner’s contact information is: City of Bozeman Public Service Department PO Box 1230 Bozeman, MT 59771-1230 The location of the South University District Phase 3, Block 4 Development is shown on the Vicinity Map in Figure 1. Stormwater Plan 3 5/12/2023 Figure 1. Vicinity Map, Bozeman, Montana Existing Site Conditions SUD Phase 3 Block 4 is a block parcel created by the South University District Phase 3 Major Subdivision. The SUD Block 4 development site was previously used agriculturally prior to its subdivision development. The existing ground slopes north at grades between 1-3%. Existing offsite drainage is minimal, if present it would flow north and west to the existing storm drainage system located along Student Drive. The stormwater management facilities for the Block 4 Development were constructed during the SUD Phase 2 infrastructure project and are located in City Park 1, northwest of the Block 4 site. A geotechnical evaluation was conducted and is provided in a separate appendix of this submittal. This site is typical of Bozeman with fine-grained soils overlying sandy silty clay to depths of approximately 7.5 to 11 feet at which point soils transition into native gravel deposits. Geotechnical borings have determined the depth to gravel ranges from 7.5 to 11 feet below existing grade. Groundwater monitoring was conducted in 2019 and 2022 during the high groundwater season for the SUD Phase 3 subdivision development. Groundwater monitoring found groundwater depths ranged from 7.0’ to 10.0’ below existing grade in the areas of the site proposed for development. The site is not located within a 100-year floodplain. Stormwater Plan 4 5/12/2023 Storm Drainage Plan Description The storm drainage plan for the SUD Phase 3 Block 4 site development consists of conveying stormwater runoff to an existing retention basin located in City Park 1 northwest of the intersection of Stucky Rd. and South 14th Ave. This pond has been constructed as a part of the Phase 2 subdivisions “Common Subdivision Improvements (CSIs)” and a 15” outfall flows to Mandeville Creek. The overall storm drainage plan for Block 4 is depicted on attached Figure 2. This plan shows proposed drainage basin areas, flow paths, and retention/infiltration system locations. In general, grades will be sloped away from buildings towards interior drive aisles. The sub-drainage areas typically drain north via curb and gutter that conveys runoff to inlets and storm drains connected to the existing retention/infiltration system located within the park. The site will be divided into 4 primary sub-drainage areas as shown on attached Figure 2 and described below. Sub Drainage Area Description The 4 primary sub-drainage areas of the Block 4 development ultimately convey runoff to an existing 30” storm pipe located within South 14th Ave at the northwest corner of the site. Sub-drainage area 30D is located on the western half of the site and extends along Arnold Street to the south and drains north to the existing 24” storm drain stub on the south side of Student Drive. Sub-area 31D is located internal to the Block 4 site and drains north to the existing 24” storm drain stub on the southeast intersection corner of Student Drive and South 13th Avenue. Sub-area 32D is located internal to the Block 4 site and drains northerly to the existing 24” storm drain stub on the southeast intersection corner of Student Drive and South 12th Avenue. Sub-area 33D is located on the eastern edge of the site and drains overland easterly and then northerly to the existing storm inlet at the intersection of South 11th Ave and Student Drive. Estimation of Runoff Runoff estimates were obtained for each sub-drainage area using City of Bozeman standards. The off-site stormwater facilities have been sized to fully capture the 10-year, 2-hour storm event. The Bozeman IDF (Intensity, Duration, and Frequency) curves show a rainfall intensity of 0.41 in/hour for the 10-year, 2-hour storm, totaling a 0.82- inch storm event. The detailed on-site and off-site basin runoff calculations are displayed in the Updated Table 4, Table 6, and Table 7 in the Appendix of this report. 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. Stormwater Plan 5 5/12/2023 Retention Facilities The exiting retention basin located in City Park 1 was designed to account for the stormwater runoff from SUD Block 4, as detailed in the updated Table 3 and Table 5 in the “South University District Phase 2 Stormwater Engineering Report” attached in the appendix of this report. The proposed Block 4 development conforms with the planned drainage areas outlined in the SUD Phase 2 Stormwater Engineering Report and is described within this report and the attached Figure 2. Conveyance Pipe Capacity Conveyance pipes were sized by adding the 25-year peak runoff rates of contributing basins without routing or attenuation. The pipe size calculations are displayed in the updated Table 4, Table 6, and Table 7 in the attached Appendix. Curb and Gutter Curb and gutter are used on the site to convey runoff into the underground storm pipe network. To ensure the standard curb design will provide adequate conveyance capacity for peak flows, curb and gutter with the greatest flows and least amount of redundant or secondary storm conveyance options was identified and analyzed for conveyance capacity. The critical curb required to convey the maximum flow was identified as the approximately 503’ length of curb running from south to north along S. 14th Ave, serving a catchment area of approximately 34,568 sf. This catchment area produces a peak flow of 1.82 cfs for the 25-year design storm. At the minimum slope of 0.5%, the curb on site has a conveyance capacity of 5.03 cfs. Table 3 – Curb and Gutter Conveyance Calculations Curb and Gutter Capacity Calcs Max Curb Conveyance Req'd (ft^3/sec) 1.82 Right-side Slope X:1 0.06 Left-side Slope X:1 33.00 Channel Bottom Width (ft) 0 Flow Depth (ft) 0.350 Flow Area (ft^2) 2.025 Wetted Perimeter (ft) 11.906 Width 0.044 Hydraulic Radius (ft) 0.170 Manning's Roughness 0.013 Slope (ft/ft) 0.005 Average Velocity (ft/sec) 2.49 Flow (ft^3/sec) 5.03 Stormwater Plan 6 5/12/2023 Storm Water Maintenance Plan The proposed storm drainage facilities will be privately operated and maintained by the Property Owners Association (POA). The POA Covenants should include the following stormwater maintenance provisions: (a) General Information. The South University District Phase 2 utilizes conventional stormwater collection to mitigate storm water impacts. The stormwater facilities consist of curb and gutter, curb inlets, sumped manholes, onsite and offsite conveyance piping, underground retention chambers, and an existing offsite detention basin located in the city park. The system is designed to accommodate all storm water from the Property. The storm water conveyance facilities located on the property are privately owned and maintained. It is the property owner association's responsibility to maintain the storm water facilities located on the property. The storm water facilities are designed to operate without excessive maintenance. However, like all infrastructure, periodic maintenance will prevent costly repair and replacement. The maintenance plan set forth in this Section has been prepared in accordance with City of Bozeman guidelines. Over time, recommended maintenance guidelines may evolve. Please contact the City of Bozeman Stormwater Division if any questions arise. (b) Storm Water Facilities Maintenance Schedule. (i) Site Housekeeping. Site housekeeping is to be conducted continuously as needed. The main cause of storm water facility damage is poor site housekeeping. Sediment tracked onto pavement can be washed into storm water inlets/ conveyance piping and damage these facilities. Trash can clog pipes and inlet structures causing property damage. Site housekeeping consists of the following: • Keep sidewalk and pavement areas clean. • Pick up trash. • Restore damaged landscaping in order to prevent sediment runoff. (ii) System Monitoring: System monitoring is to be conducted quarterly, except in winter. The storm water facilities shall be inspected quarterly to quickly identify small issues before expensive damage can occur. In addition to regular monitoring, the best time to inspect the performance of storm water facilities is during runoff events. System monitoring consists of the following: • Observe system during runoff. Look for ponding outside of stormwater inlets. This can indicate a clogged inlet or pipe. Stormwater Plan 7 5/12/2023 • Inspect inlets, manholes and pipes. (iii) Inlet, Manhole, and Piping Quarterly Maintenance: All stormwater inlets and manholes have a sump to capture sediment. If this sediment is not periodically removed it can wash downstream and clog infiltration facilities. The sump is typically visible from the surface through the inlet grate. Inlet, manhole, and piping maintenance consists of the following: • Remove visible sediment from sump. • Inspect pipe inlets and outlets for sediment in pipe and remove if present. (iv) Inlet, Manhole, and Piping Long-term Maintenance. This maintenance is to be conducted long-term if and when necessary. If regular housekeeping and maintenance is not performed adequately, sediment and debris can accumulate in the stormwater conveyance piping, and pipes may become clogged. Long-term inlet, manhole, and piping maintenance consist of the following: • Hiring a contractor to clean pipes and remove all sediment encountered from manhole sumps, inlet sumps and/or piping. (v) Retention Pond Long-term Maintenance. This maintenance is to be conducted on an annual basis at a minimum. If regular housekeeping and maintenance is not adequately performed, sediment and debris will accumulate in the underground stormwater retention basins and could negatively affect the stormwater percolation rate. Retention pond maintenance consist of the following: • Remove the underground chamber’s inspection port covers. • Record the depth from the rim of the inspection port to the chamber’s floor. If the measurement changes by 0.1’ between any reading, or sediment accumulates to a depth of 0.1’ above the bottom of the chamber, • Hire a contractor to flush and clean out the stormwater storage chambers. UPDATED Table 4: Phase 2 Inlet Basin and Pipe Capacity Calculations Inlet Drainage Basin 5.4.23 Inlet Basin 1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 D 9 D 10 D 11 D 12 D 13 D 14 D 16 D 17 D 18 D 19 D 20 D 21 D 22 D 23 D 24 D 25 D 26 D 27 D 28 D 29 D 30 D 31 D 32 D 33 D 2B 3B 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 REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU Drainage Area (acres) 0.63 0.43 1.28 0.49 0.47 1.36 0.48 0.43 0.96 0.40 0.43 1.21 0.82 0.94 0.44 1.24 0.42 0.37 0.43 0.46 1.11 1.04 0.40 0.53 1.87 1.55 0.41 0.44 5.77 2.08 4.96 1.46 0.33 0.46 0.32 Slope (%) 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 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 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 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) 325 249 784 681 300 297 320 320 249 319 316 323 279 274 331 274 335 335 354 354 360 240 327 295 762 358 300 301 500 500 500 500 287 425 275 Time of Concentration (min) 12.2 10.7 18.9 17.7 11.7 11.7 12.1 12.1 10.7 12.1 12.0 12.2 11.3 11.2 12.3 11.2 12.4 12.4 12.7 12.7 12.8 10.5 12.2 11.6 18.7 12.8 11.7 11.7 15.1 15.1 15.1 15.1 10.9 13.2 10.7 Peak Flow Calculations Design Storm 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr Intensity at Tc (Figure I-2 pg. 29) (in/hr) 2.16 2.36 1.63 1.71 2.22 2.23 2.17 2.17 2.36 2.18 2.18 2.17 2.27 2.28 2.15 2.28 2.14 2.14 2.10 2.10 2.09 2.38 2.16 2.23 1.65 2.10 2.22 2.22 1.88 1.88 1.88 1.88 2.33 2.05 2.36 Peak Runoff Rate at Tc (Q = CIA) (cfs)0.82 0.61 1.25 0.50 0.63 1.82 0.63 0.56 1.36 0.52 0.56 1.57 1.12 1.29 0.57 1.70 0.54 0.47 0.54 0.58 1.39 1.49 0.52 0.71 1.85 1.95 0.55 0.59 6.52 2.35 5.61 1.65 0.47 0.56 0.45 Note: Due to site grading changes, Basin 15 D has been omitted Detention Basin B - Pipe Network Capacity Pipe Number 1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 D 9 D 10 D 11 D 12 D 13 D 14 D 15 D 16 D 17 D 18 D 19 D 20 D 21 D 22 D 23 D 24D 25D 26D Pipe Size (in) 30.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 30.00 15.00 24.00 24.00 24.00 18.00 24.00 15.00 24.00 24.00 15.00 15.00 15.00 15.00 15.00 Manning'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 0.013 0.013 0.013 0.013 0.013 0.013 0.013 Area (ft2)4.91 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 4.91 1.23 3.14 3.14 3.14 1.77 3.14 1.23 3.14 3.14 1.23 1.23 1.23 1.23 1.23 Wetted Perimeter (ft) 7.85 3.93 3.93 3.93 3.93 3.93 3.93 3.93 3.93 3.93 3.93 7.85 3.93 6.28 6.28 6.28 4.71 6.28 3.93 6.28 6.28 3.93 3.93 3.93 3.93 3.93 Hydraulic Radius (ft) 0.63 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.63 0.31 0.50 0.50 0.50 0.38 0.50 0.31 0.50 0.50 0.31 0.31 0.31 0.31 0.31 Slope (ft/ft) 0.0219 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0079 0.0050 0.0050 0.0050 0.0045 0.0050 0.0045 0.0050 0.0045 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 Full Flow Capacity (cfs) 60.86 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 36.55 4.58 16.04 16.04 15.22 7.45 15.22 4.58 15.22 16.04 4.58 4.58 4.58 4.58 4.58 Velocity (ft/sec) 12.40 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 7.45 3.73 5.11 5.11 4.84 4.21 4.84 3.73 4.84 5.11 3.73 3.73 3.73 3.73 3.73 Contributing Inlet Basin 16D 4D NONE NONE 6D 14D NONE 21D 20D NONE 17D NONE 18D 19D 30D NONE 31D 25D 24D NONE 31D & 32D 29D 28D 6%30D NONE 33D Contributing Pipes 12D NONE 4D 5D NONE NONE 6D 9D NONE 11D NONE 14D NONE 13D 24D 17D NONE 19D NONE 22D NONE 23D NONE NONE 26D NONE 7D 15D 16D 18D 20D 21D 25D 10D Actual Pipe Flow (cfs)25.80 0.50 1.82 1.82 1.82 1.29 1.29 1.12 0.54 1.70 1.70 22.25 0.54 15.33 6.91 14.32 2.35 11.97 0.52 10.74 7.96 2.78 0.55 0.39 1.65 1.65 % Capacity 42% 11% 40% 40% 40% 28% 28% 25% 12% 37% 37% 61% 12% 96% 43% 94% 32% 79% 11% 71% 50% 61% 12% 9% 36% 36% Table 6 - Block 4 ONSITE Inlet Drainage Basin WEST - DB 30D CENTER - DRAINAGE BASIN 31D EAST - DRAINAGE BASIN 32D Inlet Basin (SDI)40 41 42 17 43 46 47 48 50 51 21 52 53 55 56 58 59 60 61 62 63 64 65 Land Use REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU Drainage Area (SF) 40408 42267 22319 10694 10272 2870 15038 14191 25386 11875 1461 20953 14743 38183 14331 13226 15222 4909 12183 17732 16328 10333 23115 Drainage Area (acres) 0.93 0.97 0.51 0.25 0.24 0.07 0.35 0.33 0.58 0.27 0.03 0.48 0.34 0.88 0.33 0.30 0.35 0.11 0.28 0.41 0.37 0.24 0.53 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 0.6 Time of Concentration (min) 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Peak Flow Calculations Design Storm 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr Intensity at Tc (Figure I-2 pg. 29) (in/hr) 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 Peak Runoff Rate at Tc (Q = CIA) (cfs)2.13 2.23 1.18 0.56 0.54 0.15 0.79 0.75 1.34 0.63 0.08 1.10 0.78 2.01 0.76 0.70 0.80 0.26 0.64 0.93 0.86 0.54 1.22 Pipe Network Capacity WEST - DB 30D CENTER - DRAINAGE BASIN 31D EAST - DRAINAGE BASIN 32D Pipe Number 40D 41D 42D 17D 43D 44D 46D 47D 48D 49D 50D 51D 21D 21bD 52D 53D 54D 55D 56D 57D 58D 59D 60D 61D 62D 63D 64D 65D Pipe Size (in) 18.00 15.00 15.00 24.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 24.00 21.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 18.00 18.00 15.00 15.00 15.00 15.00 Manning'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 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 Area (ft2)1.77 1.23 1.23 3.14 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 3.14 2.41 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.77 1.77 1.23 1.23 1.23 1.23 Wetted Perimeter (ft) 4.71 3.93 3.93 6.28 3.93 3.93 3.93 3.93 3.93 3.93 3.93 3.93 6.28 5.50 3.93 3.93 3.93 3.93 3.93 3.93 3.93 3.93 4.71 4.71 3.93 3.93 3.93 3.93 Hydraulic Radius (ft) 0.38 0.31 0.31 0.50 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.50 0.44 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.38 0.38 0.31 0.31 0.31 0.31 Slope (ft/ft) 0.0150 0.0150 0.0150 0.0200 0.0050 0.0110 0.0110 0.0150 0.0100 0.0150 0.0100 0.0100 0.0100 0.0050 0.0050 0.0050 0.0200 0.0050 0.0180 0.0100 0.0080 0.0080 0.0100 0.0100 0.0070 0.0050 0.0050 0.0050 Full Flow Capacity (cfs) 12.90 7.93 7.93 32.08 4.58 6.79 6.79 7.93 6.48 7.93 6.48 6.48 22.68 11.23 4.58 4.58 9.16 4.58 8.69 6.48 5.79 5.79 10.53 10.53 5.42 4.58 4.58 4.58 Velocity (ft/sec) 7.30 6.46 6.46 10.21 3.73 5.54 5.54 6.46 5.28 6.46 5.28 5.28 7.22 4.67 3.73 3.73 7.46 3.73 7.08 5.28 4.72 4.72 5.96 5.96 4.42 3.73 3.73 3.73 Contributing Inlet Basin 40 41 42 17 43 NONE 46 47 48 NONE 50 51 21 NONE 52 53 NONE 55 56 NONE 58 59 60 61 62 63 64 65 Contributing Pipes 41D 42D NONE 43D NONE 46D 47D 48D NONE 50D NONE NONE 52D 60D NONE 55D NONE 57D 58D NONE NONE 61D 62D 63D 64D 65D NONE 44D 49D 51D 21bD 54D 56D 53D 59D Actual Pipe Flow (cfs) 5.53 3.40 1.18 4.76 0.54 3.66 3.66 3.50 0.75 1.96 1.34 0.63 10.68 9.50 1.10 0.78 5.04 2.01 3.03 1.50 0.70 0.80 4.46 4.20 3.56 2.62 1.76 1.22 % Capacity 43% 43% 15% 15% 12% 54% 54% 44% 12% 25% 21% 10% 47% 85% 24% 17% 55% 44% 35% 23% 12% 14% 42% 40% 66% 57% 38% 27% Table 7 - Block 4 OFFSITE Inlet Drainage Basin Inlet Basin (SDI)28 29 32 33 34 35 36 37 24 15 Land Use REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU Drainage Area (SF) 16467 32398 11583 6720 15284 25878 11430 18928 1505 7301 Drainage Area (acres) 0.38 0.74 0.27 0.15 0.35 0.59 0.26 0.43 0.03 0.17 Runoff Coefficients 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Time of Concentration (min) 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Peak Flow Calculations Design Storm 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr Intensity at Tc (Figure I-2 pg. 29) (in/hr) 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 3.83 Peak Runoff Rate at Tc (Q = CIA) (cfs)0.87 1.71 0.61 0.35 0.81 1.36 0.60 1.00 0.08 0.38 Pipe Network Capacity Pipe Number 27D 28D 29D 30D 31D 32D 33D 34D 35D Pipe Size (in) 24.00 15.00 15.00 18.00 15.00 15.00 15.00 15.00 15.00 Manning's "n" (PVC) 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 Area (ft2)3.14 1.23 1.23 1.77 1.23 1.23 1.23 1.23 1.23 Wetted Perimeter (ft) 6.28 3.93 3.93 4.71 3.93 3.93 3.93 3.93 3.93 Hydraulic Radius (ft) 0.50 0.31 0.31 0.38 0.31 0.31 0.31 0.31 0.31 Slope (ft/ft) 0.0100 0.0050 0.0100 0.0150 0.0187 0.0050 0.0050 0.0050 0.0050 Full Flow Capacity (cfs) 22.68 4.58 6.48 12.90 8.86 4.58 4.58 4.58 4.58 Velocity (ft/sec) 7.22 3.73 5.28 7.30 7.22 3.73 3.73 3.73 3.73 Contributing Inlet Basin NONE 28 29 NONE NONE 32 33 34, 36 35,37 Contributing Pipes 28D NONE NONE 31D 32D 33D 34D 35D NONE 29D 40D 30D Actual Pipe Flow (cfs) 11.24 0.87 1.71 8.67 3.13 3.13 2.52 2.17 1.36 % Capacity 50% 19% 26% 67% 35% 68% 55% 47% 30% Off-site Flow SOUTH 11TH AVESOUTH 11TH AVESTUDENT DRIVESOUTH 14TH AVESTUCKY RD SOUTH 14TH AVEARNOLD ST SOUTH 14TH AVESOUTH 13TH AVESOUTH 12TH AVEEXISTINGTRAILS (TYP)SDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDLOT 2 "PHASE 1"6.41 ACRESPLAT J-518CITY PARK 14.41 ACRESPLAT J-605 LOT 1 "PHASE 1"9.82 ACRESPLAT J-518 LOT 1 "PHASE 2" 16.05 ACRES PLAT J-605 CITY PARK 2 9.64 ACRES PLAT J-605 LOT 1, BLOCK 4 "PHASE 3" 11.89 ACRES PLAT J-695 SDBASIN 40 BASIN 41 BASIN 42 BASIN 48 BASIN 47 BASIN 50 BASIN 51 BASIN 58 BASIN 59 BASIN 55 BASIN 17 BASIN 43 BASIN 46 BASIN 53 BASIN 56 BASIN 52 BASIN 21 BASIN 60 BASIN 61 BASIN 63 BASIN 62 BASIN 65 BASIN 64 PIPE 27D PIPE 28D PIPE 29D PIPE 30D PIPE 31D PIPE 32D PIPE 33D PIPE 34D PIPE 34D PIPE 35D PIPE 40D PIPE 41D PIPE 42D PIPE 17D PIPE 43D PIPE 44D PIPE 46D PIPE 47DPIPE 48D PIPE 49D PIPE 51D PIPE 50D PIPE 21D PIPE 52D PIPE 21bDPIPE 55D PIPE 54D PIPE 60D PIPE 61D PIPE 56D PIPE 57D PIPE 58D PIPE 59D PIPE 62D PIPE 63D PIPE 64D PIPE 65D DRAINAGE BASIN 30D PHASE 3 4.98 ac 5.77 ac DRAINAGE BASIN 31D PHASE 3 4.55 ac 2.08ac DRAINAGE BASIN 32DPHASE 32.06 ac 4.96acDRAINAGE BASIN 33DPHASE 3 / 11TH AVE2.58 ac 1.46 acBASIN 24 BASIN 29 BASIN 15 BASIN 28 BASIN 33 BASIN 35 BASIN 34 BASIN 37 BASIN 36 EX PIPE 24D EX PIPE 15D ALLISON SUBDIVISION, PH 4A BLOCK 1, LOT 2 8.39 ACRES ALLISON SUBDIVISION, PH 4A BLOCK 1, LOT 3A 14.42 ACRES ALLISONBASIN 19D 0.20 ac 0.37 acDETENTIONBASIN PHASES2 AND 3PHASE 1B PHASE 1BASIN 1D0.63 ac BASIN 2D0.43 ac BASIN 3D1.28 ac BASIN 4D 0.49 acBASIN 5D0.47 acBASIN 6D1.36 ac BASIN 7D0.48 acBASIN 8D0.43 acBASIN 9D0.96 ac BASIN 10D0.40 acBASIN 11D0.43 acBASIN 12D1.21 ac BASIN 13D0.82 ac BASIN 14D 0.94 ac BASIN 16D0.44 acBASIN 17D 1.24 ac BASIN 18D 0.42 ac BASIN 20D0.43 acBASIN 21D0.46 acBASIN 22D 1.11 ac BASIN 26D 1.87 ac BASIN 27D 1.55 ac BASIN 23D 1.04 ac BASIN 24D 0.40 ac BASIN 28D 0.41 ac BASIN 2B 0.33 ac BASIN 3B 0.46 acBASIN 4B0.32 acDETENTIONBASIN PHASES2 AND 3PHASE 1B PHASE 1 BASIN 25D 0.20 ac 0.53ac BASIN 29D 0.20 ac 0.44 ac MAIL LOADINGZONE PIPE 53D BASIN 32 >>SDSDSDSDSD SD SD SDHCHC HC HC HC HC HC HC HC HCHC HCHCHCHCHCHCSDSDSDSDSDSDSDSDSDSDSDSD SD SD SD SD SDSDSD SDSDSDSD SDSDSD SDSDSDSD SD SD SD SD SD SD SD SD SD SD SD SD SDSDSDSDSD SD SDSDSDSD SD SD SD SD SD SD SDSDSDSD SDSDSDSDSDSDSDHCHC HCHCSDSDSDSDSDSDSDSDSDSDSD SDSDSDSDSDSDSDSDSDSDSDSDSD SD SD SDSDSDSDSDSDSDSDSD SD SDSDSDSDSD SDSDSDSDSDSDSDSDSD SD SD SDSD SD SD SD SD SD SDSDSDSDSDSDSDSDSDSDSDSDSDSDSD SD SDSDSDSDSDSDSD STORM WATER Figure 2STORMDRAINAGEFIGURE1 3/23/2022 COB CONCEPT SUBMITTAL ZWL CDP 2 10/17/2022 COB SITE PLAN SUBMITTAL ZWL CDP PROFESSIONALENGINEERS &SURVEYORSSTAHLYENGINEERING& ASSOCIATESTHE FLATS AT BOZEMAN CAPSTONE COLLEGIATE COMMUNITIES LLC OFF-SITE STORM FACILITIES PH. 3 STORM FACILITIES PH. 3 SITE STORM FACILITIES PH. 3 SUBD. STORM FACILITIES Storm Water Plan South University District Phase 2 June, 2017 Submitted to: City of Bozeman Engineering Department 20 East Olive Bozeman, MT 59715 Prepared by: Stahly Engineering and Associates 851Bridger Drive, Suite 1 Bozeman, MT 59715 (406) 522-9526 Storm Water Plan 1 6/27/2017 Storm Water Plan Contents General Information Existing Conditions and General Design Criteria Storm Drainage Plan Description Estimation of Runoff 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 Figure 2. Inlet Basin Exhibit Table 1. Runoff Calculations – Phase 2 & 3 Table 2. Outfall Structure Sizing Table 3. Curb and Gutter Capacity Calculations Table 4. Phase 2 Inlet Basin and Pipe Capacity Calculations Table 5. Phase 2 and 3 Detention Basin Calculations Storm Water Plan 2 6/27/2017 General Information The South University District (SUD) Phase 2 is a subsequent minor subdivision of Lot 3, SUD Subdivision Phase 1. The subsequent division will provide right of way dedications for South 14th Avenue, South 11th Avenue, and an additional street on the south side (currently un-named). This subdivision will create a 16.05-acre lot for subsequent site development. Phase 2 is located within the City of Bozeman, south of Campus Boulevard and between South 11th and South 14th Avenues. Phase 2 is located south of Phase 1 (completed) and Phase 1B (in progress). Site development on the Phase 2 lot is anticipated to be an 887-bed student housing project. SUD Phase 3 is a future development planned south of Phase 2. SUD Phase 3 will utilize storm water infrastructure installed in Phase 2 and its area is included in this analysis. Storm drainage improvements for SUD Phase 2 utilize infrastructure in Campus Blvd. and the Phase 1 Park. The storm water detention basin serving Phase 2 and 3 was constructed with the Phase 1 Park improvements. A storm water trunk line was installed in Campus Boulevard for Phase 2 and 3. This report also includes a preliminary analysis of Phase 2 on-site storm water mains. The analysis of on-site mains will be re-evaluated and updated with the final site design. The developer’s contact information is: Capstone Collegiate Communities, LLC. 431 Office Park Drive Birmingham, AL 35223 Existing Conditions and General Design Criteria As stated previously the detention basin and trunk line in Campus Blvd. serving Phase 2 and Phase 3 was constructed in Phase 1. The existing storm water detention basin is located in the Phase 1 Park and outfalls to Mandeville Creek. The Phase 1 Park is located between Phase 2 and Mandeville creek to the west. The existing condition at the site is undeveloped agricultural land. The site generally slopes to the north at 1-2%. In accordance with the City of Bozeman Design Standards and Specifications Policy (COB Standards) an engineering analysis has been conducted for SUD Phase 2 and 3 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, the detention basin 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. Storm Water Plan 3 6/27/2017 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 Description The overall storm drainage plan for SUD Phase 2 is depicted on Figure 1 and 2 at the end of this report. Figure 1 shows the Phase 2 improvements, and Figure 2 shows the inclusion of Phase 3 areas. The storm drainage system builds on improvements completed in Phase 1 in the Park and Campus Blvd. Overall drainage direction on the proposed development is indicated by arrows showing the proposed drainage patterns and inlet locations. The existing detention pond previously constructed during Phase 1 will not need to be altered to accommodate Phase 2 or 3. Phase 2 storm water mains will connect to the trunk line in Campus Blvd. A storm drain will be extended in South 14th Avenue and along the south boundary of Phase 2 to serve future development in Phase 3. Estimation of Runoff Runoff estimates are provided for Phase 2 (21.4 acres) and Phase 3 (14.2 acres), with Phase 3 located to the south of Phase 2. Phase 3 estimates are included in this report because the storm water runoff from this offsite area will pass through Phase 2 storm water infrastructure. 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 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 2 and 3 A runoff coefficient of 0.20 for open land was selected for pre-development conditions. An average overland slope of 1.1% over a basin length of 1,200 feet provides a time of concentration of 56.5 minutes. The Bozeman IDF curves show a rainfall intensity for the 10-year design storm event of 0.67 in/hr. Applying this over the 35.6 acre site produces a runoff flow rate of 4.74 cfs at the downstream end of the basin. Post-development Runoff – Phase 2 and 3 Post-construction runoff was calculated using a runoff coefficient of 0.60 (commercial neighborhood) to account for future site development in accordance Storm Water Plan 4 6/27/2017 with the master plan. The increased impervious area and proposed site grading reduces the time of concentration to 14.7 minutes. The Bozeman IDP curves show a 10-year storm intensity of 1.59 in/hr. The rational method provides a 10- year peak runoff rate of 34.07 cfs. The same analysis for a 25-year event provides a peak runoff rate of 44.43 cfs. Table 1: Runoff Calculations – Phase 2 and 3 Time of Concentration Calculations Preconstruction Postconstruction Storm Sewer Flow Land Use Open Land REMU REMU Drainage Area (acres) 35.6 35.6 35.6 Slope (%) 1.1 1.8 1.8 Runoff Coefficients 0.2 0.6 0.6 Frequency Adjustment Factor, Cf 1 1 1.1 Basin Length (ft) 1200 367 367 Time of Concentration (min) 56.5 14.7 13.0 Peak Flow Calculations Design Storm 10-Year 10-Year 25-Year Intensity at Tc (Figure I-2 pg. 29) (in/hr) 0.67 1.59 2.08 Peak Runoff Rate at Tc (Q = CIA) (cfs) 4.74 34.07 44.43 In addition to the overall storm runoff calculations for Phase 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 4 at the end of this report. Storage/Treatment Facilities Simple pond routing using the modified rational method is provided for Phase 2 and Phase 3 in Table 5 at the end of the report. This spreadsheet shows a required storage of 32,151 cubic feet of runoff for the 10-year event for Phase 2 and 3. The required storage is provided by a detention basin that was constructed during Phase 1. The detention basin constructed in Phase 1 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 4933.0. This 1.5’ maximum depth provides a total volume of approximately 36,500 cubic feet. The detention basin is located at the northwest (down-gradient) end of the site and is vegetated with grass. Storm Water Plan 5 6/27/2017 Outfall Structure Weir Sizing The detention basin outflow for both Phase 2 and 3 developments 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 the outlet structure was determined (See Table 2). The combined slot width for Phase 2 and 3 discharge structure is 9 inches. This slot width limits the discharge from the structure to pre-developed rates at the maximum depth of 1.5 feet. Since this detention pond was constructed during Phase 1, this outfall structure has already been constructed and meets the requirements of Phase 2 and 3. Table 2 Outfall Structure Weir Sizing Phase 2-3 Pre-developed Runoff (cfs) 4.47 Weir Coefficient "C" 3.33 Head (ft) 1.5 Slot Width (in) 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 1.95 cfs of runoff. The capacity of the curb at the lowest designed slope of 0.6% is 5.51 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. Table 3 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 Manning's Roughness 0.013 Slope (ft/ft) 0.006 Average Velocity (ft/sec) 2.72 Flow (ft^3/sec) 5.51 Storm Water Plan 6 6/27/2017 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. Table 5 Phase 2 and Phase 3 Detention Basin Calculations Time of Concentration Calculations Preconstruction Postconstruction Storm Sewer Flow Land Use Open Land REMU REMU Drainage Area (acres)35.6 35.6 35.6Slope (%)1.1 1.8 1.8 Runoff Coefficients 0.2 0.6 0.6Frequency Adjustment Factor, Cf 1 1 1.1 Basin Length (ft)1200 367 367 Basin length based on typical inlet areaTime of Concentration (min)56.5 14.7 13.0 Peak Flow Calculations Design Storm 10-Year 10-Year 25-YearIntensity at Tc (Figure I-2 pg. 29) (in/hr)0.67 1.59 2.08 Peak Runoff Rate at Tc (Q = CIA) (cfs)4.74 34.07 44.43 (max release rate) Required Storage Volume MAX VOL. 32151.02 Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage(minutes)(in/hr)(Q = CIA) (cfs)(cf)(cf)(cf) 2 5.84 124.71 14965.50 568.75 14396.7543.72 79.48 19074.44 1137.49 17936.94 6 2.86 61.06 21982.84 1706.24 20276.5982.37 50.65 24311.53 2274.99 22036.54 10 2.05 43.81 26286.38 2843.74 23442.64121.82 38.91 28018.46 3412.48 24605.97 14 1.65 35.20 29571.65 3981.23 25590.42161.51 32.28 30986.52 4549.98 26436.54 18 1.40 29.90 32290.60 5118.73 27171.88201.31 27.92 33503.59 5687.47 27816.11241.16 24.80 35711.22 6824.97 28886.25 26 1.10 23.54 36725.82 7393.72 29332.10281.05 22.44 37690.86 7962.46 29728.40 30 1.00 21.45 38612.08 8531.21 30080.87320.96 20.57 39494.20 9099.96 30394.24 34 0.93 19.78 40341.16 9668.70 30672.46360.89 19.05 41156.33 10237.45 30918.88380.86 18.40 41942.57 10806.20 31136.37 40 0.83 17.79 42702.35 11374.95 31327.40420.81 17.24 43437.82 11943.69 31494.13 44 0.78 16.72 44150.87 12512.44 31638.42460.76 16.25 44843.14 13081.19 31761.95 48 0.74 15.80 45516.12 13649.94 31866.18500.72 15.39 46171.11 14218.68 31952.42 52 0.70 15.00 46809.28 14787.43 32021.85540.69 14.64 47431.69 15356.18 32075.51560.67 14.30 48039.29 15924.92 32114.37 58 0.65 13.97 48632.95 16493.67 32139.27600.64 13.67 49213.44 17062.42 32151.02 Required Storage 62 0.63 13.38 49781.49 17631.17 32150.32640.61 13.11 50337.75 18199.91 32137.83 66 0.60 12.85 50882.82 18768.66 32114.16680.59 12.60 51417.26 19337.41 32079.85 70 0.58 12.37 51941.57 19906.16 32035.42720.57 12.14 52456.24 20474.90 31981.34740.56 11.93 52961.70 21043.65 31918.05 76 0.55 11.72 53458.35 21612.40 31845.95780.54 11.53 53946.58 22181.15 31765.43 80 0.53 11.34 54426.73 22749.89 31676.84820.52 11.16 54899.15 23318.64 31580.51 84 0.51 10.98 55364.14 23887.39 31476.75860.51 10.82 55821.98 24456.13 31365.85880.50 10.66 56272.95 25024.88 31248.07 90 0.49 10.50 56717.32 25593.63 31123.69 92 0.48 10.35 57155.30 26162.38 30992.93 94 0.48 10.21 57587.14 26731.12 30856.02960.47 10.07 58013.05 27299.87 30713.18 98 0.47 9.94 58433.23 27868.62 30564.611000.46 9.81 58847.88 28437.37 30410.511020.45 9.68 59257.16 29006.11 30251.05 104 0.45 9.56 59661.26 29574.86 30086.401060.44 9.44 60060.35 30143.61 29916.74 108 0.44 9.33 60454.56 30712.36 29742.211100.43 9.22 60844.07 31281.10 29562.96 112 0.43 9.11 61228.99 31849.85 29379.141140.42 9.01 61609.47 32418.60 29190.87 116 0.42 8.91 61985.64 32987.34 28998.291180.41 8.81 62357.61 33556.09 28801.521200.41 8.71 62725.51 34124.84 28600.67 Notes Table 4: Phase 2 Inlet Basin and Pipe Capacity CalculationsInlet Drainage BasinInlet Basin 1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 D 9 D 10 D 11 D 12 D 13 D 14 D 16 D 17 D 18 D 19 D 20 D 21 D 22 D 23 D 24 D 25 D 26 D 27 D 28 D 29 D 30 D 31 D 32 D33 D2B 3B 4BLand UseREMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMUREMUREMU REMU REMUDrainage Area (acres)0.63 0.43 1.28 0.49 0.47 1.36 0.48 0.43 0.96 0.40 0.43 1.21 0.82 0.94 0.44 1.24 0.42 0.20 0.43 0.46 1.11 1.04 0.40 0.20 1.87 1.55 0.41 0.20 4.98 4.552.06 2.580.33 0.46 0.32Slope (%)1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.80 1.801.802.1 2.1 2.1Runoff Coefficients0.6 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 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.60.60.6 0.6 0.6Frequency Adjustment Factor, Cf1.1 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 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.11.11.1 1.1 1.1Basin Length (ft)325 249 784 681 300 297 320 320 249 319 316 323 279 274 331 274 335 335 354 354 360 240 327 295 762 358 300 301 375 375 375375287 425 275Time of Concentration (min)12.2 10.7 18.9 17.7 11.7 11.7 12.1 12.1 10.7 12.1 12.0 12.2 11.3 11.2 12.3 11.2 12.4 12.4 12.7 12.7 12.8 10.5 12.2 11.6 18.7 12.8 11.7 11.7 13.1 13.1 13.113.110.9 13.2 10.7Peak Flow CalculationsDesign Storm 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr25yr25yr 25yr 25yrIntensity at Tc (Figure I-2 pg. 29) (in/hr) 2.16 2.36 1.63 1.71 2.22 2.23 2.17 2.17 2.36 2.18 2.18 2.17 2.27 2.28 2.15 2.28 2.14 2.14 2.10 2.10 2.09 2.38 2.16 2.23 1.65 2.10 2.22 2.22 2.07 2.07 2.072.072.33 2.05 2.36Peak Runoff Rate at Tc (Q = CIA) (cfs)0.82 0.61 1.25 0.50 0.63 1.82 0.63 0.56 1.36 0.52 0.56 1.57 1.12 1.29 0.57 1.70 0.54 0.26 0.54 0.58 1.39 1.49 0.52 0.27 1.85 1.95 0.55 0.27 6.17 5.64 2.553.200.47 0.56 0.45Note: Due to site grading changes, Basin 15 D has been omittedDetention Basin B - Pipe Network CapacityPipe Number1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 D 9 D 10 D 11 D 12 D 13 D 14 D 15 D 16 D 17 D 18 D 19 D 20 D 21 D 22 D 23 D 24D25D 26DPipe Size (in)30.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 30.00 15.00 24.00 24.00 24.00 18.00 24.00 15.00 24.00 24.00 15.00 15.00 15.0015.00 15.00Manning's "n" (PVC)0.013 0.013 0.013 0.013 0.013 0.013 0.0130.013 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 0.0130.013 0.013Area (ft2)4.91 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.23 4.91 1.23 3.14 3.14 3.14 1.77 3.14 1.23 3.14 3.14 1.23 1.23 1.231.23 1.23Wetted Perimeter (ft)7.85 3.93 3.93 3.93 3.93 3.93 3.93 3.933.93 3.93 3.93 7.85 3.93 6.28 6.28 6.28 4.71 6.28 3.93 6.28 6.28 3.93 3.93 3.933.93 3.93Hydraulic Radius (ft)0.63 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.63 0.31 0.50 0.50 0.50 0.38 0.50 0.31 0.50 0.50 0.31 0.31 0.310.31 0.31Slope (ft/ft)0.0219 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0079 0.0050 0.0050 0.0050 0.0045 0.0050 0.0045 0.0050 0.0045 0.0050 0.0050 0.0050 0.00500.0050 0.0050Full Flow Capacity (cfs)60.86 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 4.58 36.55 4.58 16.04 16.04 15.22 7.45 15.22 4.58 15.22 16.04 4.58 4.58 4.584.58 4.58Velocity (ft/sec)12.40 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 3.73 7.45 3.73 5.11 5.11 4.84 4.21 4.84 3.73 4.84 5.11 3.73 3.73 3.733.73 3.73Contributing Inlet Basin16D 4D NONE NONE 6D 14D NONE 21D 20D NONE 17D NONE 18D 19D94%30DNONE 31D 25D 24D NONE 31D and 32D 29D 28D6%30DNONE 33DContributing Pipes12D NONE 4D 5D NONE NONE 6D 9D NONE 11D NONE 14D NONE 13D 24D 17D NONE 19D NONE 22D NONE 23D NONE NONE26D NONE7D15D16D18D20D21D25D10DActual Pipe Flow (cfs)23.51 0.50 1.82 1.82 1.82 1.29 1.29 1.12 0.54 1.70 1.70 19.96 0.54 13.79 6.17 12.99 0.00 12.99 0.52 12.20 8.19 4.01 0.55 0.373.20 3.20% Capacity39% 11% 40% 40% 40% 28% 28% 25% 12% 37% 37% 55% 12% 86% 38% 85% 0% 85% 11% 80% 51% 88% 12% 8%70% 70%Detention Basin B - Pipe Network CapacityPipe Number1 B 2 B 3 B 10 B 11 B 12 B 13 B 1E 4 B 5 B 6 B 7 B 8 B 9 B 1F 2F 3F 4F 5F 6F 7F 8F 9F 10F 11F 12FPipe Size (in)36.00 36.00 30.00 12.00 12.00 30.00 24.00 15.00 30.00 12.00 30.00 24.00 15.00 12.00 24.00 15.00 24.00 15.00 15.00 15.00 18.00 15.00 15.00 15.00 15.00 15.00Manning'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 0.013 0.013 0.013 0.013 0.013 0.013 0.013Area (ft2)7.07 7.07 4.91 0.79 0.79 4.91 3.14 1.23 4.91 0.79 4.91 3.14 1.23 0.79 3.14 1.23 3.14 1.23 1.23 1.23 1.77 1.23 1.23 1.23 1.23 1.23Wetted Perimeter (ft)9.42 9.42 7.85 3.14 3.14 7.85 6.28 3.93 7.85 3.14 7.85 6.28 3.93 3.14 6.28 3.93 6.28 3.93 3.93 3.93 4.71 3.93 3.93 3.93 3.93 3.93Hydraulic Radius (ft)0.75 0.75 0.63 0.25 0.25 0.63 0.50 0.31 0.63 0.25 0.63 0.50 0.31 0.25 0.50 0.31 0.50 0.31 0.31 0.31 0.38 0.31 0.31 0.31 0.31 0.31Slope (ft/ft)0.0060 0.0060 0.0045 0.0100 0.0100 0.0230 0.0100 0.0050 0.0045 0.0050 0.0045 0.0100 0.0045 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050 0.0050Full Flow Capacity (cfs)51.80 51.80 27.59 3.57 3.57 62.37 22.68 4.58 27.59 2.53 27.59 22.68 4.35 2.53 16.04 4.58 16.04 4.58 4.58 4.58 7.45 4.58 4.58 4.58 4.58 4.58Velocity (ft/sec)7.33 7.33 5.62 4.55 4.55 12.71 7.22 3.73 5.62 3.22 5.62 7.22 3.54 3.22 5.11 3.73 5.11 3.73 3.73 3.73 4.21 3.73 3.73 3.73 3.73 3.73Contributing Inlet BasinNONE NONE NONE 4B 1D 5D 8D 7D 2D 2B NONE NONE 3D 3B 11D 10D NONE 9D 12D 13D 26D 22D NONE 23D NONE 27DContributing Pipes2B 3B 13B NONE NONE 2D 1E NONE 5B NONE 7B 1F 9B NONE 3F NONE 4F NONE 6F NONE 8F NONE 10F NONE 12F NONE10B 4B3D 8D6B8B2F5F9F11F11B1D7F12BActual Pipe Flow (cfs)44.74 44.74 17.01 0.45 0.82 26.46 2.31 0.63 14.70 0.47 13.63 11.81 1.82 0.56 11.81 0.52 10.73 1.36 2.69 1.12 6.68 1.39 3.44 1.49 1.95 1.95% Capacity86% 86% 62% 13% 23% 42% 10% 14% 53% 18% 49% 52% 42% 22% 74% 11% 67% 30% 59% 24% 90% 30% 75% 32% 43% 43%