Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
20 - Design Report - Public Safety Center - Storm
Page 1 of 3 Storm Drainage Report City of Bozeman - Public Safety Center December 16, 2019 Revised March 17, 2020 Revised August 17, 2020 1 Introduction This summary report provides hydrologic and hydraulic calculations for sizing of retention storage facilities, pipes and other storm drainage structures for the proposed Bozeman Public Safety Center, located on the west side of Rouse Avenue between Oak Street and Tamarack Street in Bozeman, Montana. The purpose of the report and calculations is to demonstrate the following: - Post-development peak runoff does not exceed pre-construction (historic) conditions for the 10-year storm event. - The 25-year peak runoff is conveyed by underground storm drain facilities with no surface overflow. - Storm water treatment is provided to intercept and contain sediment and floating debris on site, for eventual removal and disposal. 2 Drainage Patterns Existing Conditions: The site is a “brownfield” site with almost no vegetation. It was previously a maintenance facility used by the Montana Department of Transportation. Prior to currently ongoing demolition, the site housed offices, maintenance buildings, tanks, stockpiled soil and aggregate materials, maintenance vehicles and other miscellaneous support facilities, and was almost entirely surfaced with asphalt, concrete or gravel. Topography slopes from south to north at about 2 percent. Pre-development, existing (historic) runoff is illustrated on Figure 1 (Pre-Development Drainage Map). Runoff from Basin H1 currently drains north to Oak Street, collects in two curb inlets and is piped east to Bozeman Creek. Runoff from Basin H2 drains south to Tamarack Street storm drain. Runoff from Basin H3 drains to Rouse Avenue. Rouse Avenue currently has no curb & gutter in this area, but a project by the Montana Department of Transportation is currently underway to install curb, gutter and sidewalk within the right-of-way. Runoff from Basin H4 drains to a ditch that runs west along the south side of Oak Street. The calculations for pre-development runoff are based on undeveloped conditions (Rational runoff coefficient = 0.20), rather than the mostly impervious surfaces that currently exist (coefficient of about 0.85). This assumption greatly restricts post-development runoff to offsite areas, holding the site to a much higher standard and greatly reducing site runoff as compared to existing conditions. Proposed Improvements: The site will be cleared for a new building, various utilities and storm drainage facilities, parking lots, sidewalks, and new surface improvements. Vegetated swales and retention Page 2 of 3 areas will be incorporated throughout the project, providing opportunities for uptake of nutrients and other treatment processes. Storm runoff will be routed to numerous surface and underground retention areas for all runoff resulting from a 10-year storm event; therefore, detention control structures (for controlled release and attenuation of peak runoff) are not required. The storm drain system is sized to convey the 25-year peak runoff to the retention facilities. Site grading will provide for overland conveyance of excess runoff from larger storms. There will be no post-development direct runoff to Rouse Avenue (pre-development basin H3), so there is no associated sub-basin D3. Post-development direct runoff leaving the site is identified as sub-basins D1.1, D2, D3 (i.e., D3.1+D3.2+D3.3) and D4, all of which have much lower peak runoff rates than under existing conditions (sub-basins H1, H2, H3 and H4). Post-development runoff is illustrated on Figure 2 (Post-Development Drainage Map). Sub-basins are listed on the “Runoff Calculations” table in the attached calculations. From this table, pre- and post-development peak runoff to offsite areas is summarized below: Peak Runoff Rate (cfs) Sub-basin 2-year 10-year 25-year H1 (pre-development) 1.20 2.31 2.77 D1.1 0.07 0.13 0.16 H2 (pre-development) 0.09 0.19 0.22 D2 0.07 0.14 0.17 H3 (pre-development) 0.21 0.41 0.49 D3 (D3.1+D3.2+D3.3) 0.07 0.15 0.18 H4 (pre-development) 0.13 0.26 0.31 D4 0.01 0.01 0.02 3 Retention Calculations Except for the direct runoff sub-basins listed above (D1.1, D2, D3 and D4), all post-development runoff will be routed to a combination of underground and above-ground retention storage facilities, sized for full retention per City of Bozeman Design Standards. Numerous above-ground retention storage areas are proposed. Sub-basins D1.5 through D1.7, D1.13 and D1.14 each drain to their own individual onsite surface retention area (i.e., closed depression). Sub-basins D1.2 through D1.4 each drain to a 48-inch diameter concrete dry well surrounded by geotextile enclosed, washed rock backfill. Calculations are provided for the water storage volume available in each dry well. Sub-basins D1.8 through D1.11 drain to an underground storage facility located under the north parking lot of sub-basin D1.8. Sub-basin D1.12 drains to a combination of underground and above-ground retention storage located east of the proposed building. Page 3 of 3 Sub-basins are linked by surface or piped overflow to allow excess runoff to continue downstream without flooding surface improvements. Runoff in excess of retention volumes is routed downstream. To address City of Bozeman development standards, 25-year peak runoff is piped underground to the retention facilities. Retention calculations are summarized page 1 of the attached calculations. 4 Conveyance The proposed storm drain system is shown on Figure 2. Pipes were sized to convey the 25-year peak runoff. Drop inlets and curb inlets have been placed where needed to limit the spread of water and ponding. Provisions for overland flow of larger, less frequent storms up to the 100-year storm will be incorporated into the site grading. Supporting calculations are attached. Design details will be provided on the construction drawings. Bozeman Public Safety Center Peak Runoff Calculations *** Revised 8/17/19; added D1.12A MODIFIED RATIONAL METHOD i = A * (Tc/60) B Qp = C i A Qp = peak runoff, cfs Design Coefficients C = runoff coefficient Storm AB i = A(Tc/60)B (Bozeman IDF curve)2-yr 0.36 -0.60 Tc = time of concentration, minutes 5-yr 0.52 -0.64 A = Area, acres 10-yr 0.64 -0.65 25-yr 0.78 -0.64 50-yr 0.92 -0.66 Retention Volume = 7,200*(C)*(i)*(A), where i = 0.41 in./hr 100-yr 1.01 -0.67 (Bozeman Design Standards, March 2004) Retention Sub-Basin Name Area C Tc Q2 Q5 Q10 Q25 Q50 Q100 Volume (ft.3) Basin 1 H1 6.26 0.20 11.75 1.20 1.85 2.31 2.77 3.38 3.77 D1.1 (direct) 0.15 0.28 5.00 0.07 0.11 0.13 0.16 0.20 0.22 D1.2 (ret.) 0.17 0.34 5.00 0.09 0.15 0.19 0.22 0.28 0.31 172 D1.3 (ret.) 0.18 0.43 5.00 0.12 0.20 0.25 0.30 0.37 0.42 230 D1.4 (ret.) 0.24 0.55 5.00 0.21 0.34 0.43 0.51 0.63 0.71 391 D1.5 (ret.) 0.09 0.47 5.00 0.07 0.11 0.14 0.16 0.20 0.23 126 D1.6 (ret.) 0.22 0.64 5.00 0.23 0.36 0.46 0.54 0.67 0.76 419 D1.7 (ret.) 0.46 0.54 5.00 0.40 0.64 0.80 0.95 1.18 1.33 735 D1.8 0.25 0.68 5.00 0.27 0.43 0.55 0.65 0.81 0.91 D1.9 0.52 0.90 5.00 0.75 1.19 1.51 1.79 2.22 2.50 D1.10 0.35 0.86 5.00 0.48 0.77 0.97 1.15 1.42 1.60 D1.11 1.58 0.90 5.00 2.26 3.61 4.56 5.42 6.72 7.56 D1.8 through D1.11 (ST1) 2.70 0.87 5.00 3.77 6.01 7.58 9.01 11.17 12.57 6,952 D1.12 (ST2+ret.) 2.28 0.71 5.00 2.58 4.12 5.19 6.17 7.65 8.61 4,763 D12A (to SDMH #11) 1.07 0.69 5.00 1.18 1.88 2.37 2.82 3.50 3.94 D1.13A 0.22 0.50 5.00 0.17 0.28 0.35 0.42 0.52 0.58 D1.13B 0.24 0.90 5.00 0.34 0.55 0.69 0.82 1.02 1.15 D1.13A+D1.13B (ret.) 0.46 0.71 5.00 0.52 0.83 1.04 1.24 1.54 1.73 958 D1.14 (ret.) 0.55 0.67 5.00 0.59 0.94 1.18 1.41 1.75 1.97 1,087 Basin 2 H2 0.29 0.20 5.00 0.09 0.15 0.19 0.22 0.28 0.31 D2 (direct) 0.15 0.30 5.00 0.07 0.11 0.14 0.17 0.21 0.24 Basin 3 H3 0.93 0.20 8.93 0.21 0.33 0.41 0.49 0.60 0.67 D3.1 0.09 0.24 5.00 0.03 0.05 0.07 0.08 0.10 0.11 D3.2 0.05 0.23 5.00 0.02 0.03 0.04 0.04 0.05 0.06 D3.3 0.07 0.20 5.00 0.02 0.04 0.05 0.05 0.07 0.07 D3.1+D3.2+D3.3 (direct) 0.21 0.22 5.00 0.07 0.12 0.15 0.18 0.22 0.25 Basin 4 H4 0.40 0.20 5.00 0.13 0.20 0.26 0.31 0.38 0.43 D4 (direct) 0.02 0.20 5.00 0.01 0.01 0.01 0.02 0.02 0.02 Bozeman Public Safety Center Runoff Coefficients (Rational Method) *** Revised 8/17/19; added D1.12A Area Area (sq. ft.) Runoff INPUT Sub-Basin (acres) Total Pervious Impervious Coefficient Pervious Impervious Basin 1 H1 6.26 272,686 272,686 0 0.20 D1.1 (direct) 0.15 6,534 5,820 714 0.28 714 D1.2 (ret.) 0.17 7,405 5,903 1,502 0.34 1,502 D1.3 (ret.) 0.18 7,841 5,232 2,609 0.43 2,609 D1.4 (ret.) 0.24 10,454 5,201 5,253 0.55 5,253 D1.5 (ret.) 0.09 3,920 2,394 1,526 0.47 1,526 D1.6 (ret.) 0.22 9,583 3,493 6,090 0.64 3,493 D1.7 (ret.) 0.46 20,038 10,263 9,775 0.54 10,263 D1.8 0.25 10,890 3,390 7,500 0.68 3,390 D1.9 0.52 22,651 0 22,651 0.90 D1.10 0.35 15,246 917 14,329 0.86 917 D1.11 1.58 68,825 356 68,469 0.90 356 D1.8 through D1.11 (ST1) 2.70 117,612 0.87 D1.12 (ST2+ret.) 2.28 99,317 27,281 72,036 0.71 27,281 D12A (to SDMH #11) 1.07 46,609 14,019 32,590 0.69 14,019 D1.13A 0.22 9,583 5,517 4,066 0.50 4,066 D1.13B 0.24 10,454 60 10,394 0.90 60 D1.13A+D1.13B (ret.) 0.46 20,038 0.71 D1.14 (ret.) 0.55 23,958 7,892 16,066 0.67 7,892 Basin 2 H2 0.29 12,632 12,632 0 0.20 D2 (direct) 0.15 6,534 5,598 936 0.30 936 Basin 3 H3 0.93 40,511 40,511 0 0.20 D3.1 0.09 3,920 3,716 204 0.24 204 D3.2 0.05 2,178 2,088 90 0.23 90 D3.3 0.07 3,049 3,049 0 0.20 D3.1+D3.2+D3.3 (direct) 0.21 9,148 0.22 Basin 4 H4 0.40 17,424 17,424 0 0.20 D4 (direct) 0.02 871 871 0 0.20 Record Id: H1 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Fallow Fields of Loose Soil Surface. 0.05 40.00 ft 1.75% 0.05 1.20 in 3.3672 min Shallow Nearly bare ground (n=0.025) 80.00 ft 1.25% 0.025 0.9288 min Int Channel Earth-lined (n=0.025) 365.00 ft 1.15% 0.025 2.7831 min Int Channel bare ground 520.00 ft 0.83% 0.025 4.6671 min Pervious TC 11.7461 min Record Id: H2 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet bare ground 45.00 ft 2.0% 0.03 1.20 in 2.3308 min Int Channel Concrete curb & gutter 340.00 ft 0.6% 0.012 1.7228 min Pervious TC 4.0536 min Record Id: H3 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Range (natural). 0.13 20.00 ft 1.0% 0.13 1.20 in 5.1956 min Int Channel Other 930.00 ft 1.12% 0.013 3.7365 min Pervious TC 8.9321 min Record Id: H4 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Short prairie grass and lawns. 0.15 55.00 ft 2.36% 0.025 1.20 in 2.2138 min Int Channel Grassed (n=0.030) 310.00 ft 1.19% 0.03 2.7884 min Pervious TC 5.0022 min Bozeman Public Safety Center Sub-Basin D1.8 through D1.11 (ST1) Storage Calculations (10-yr storm) StormTech Sizing Calculations Required Storage Volume 6,952 ft3 StormTech Modules, Model No. SC740 (30" chamber height) Depth to top of gravel 36 in. installed storage volume 68.14 ft3 per chamber (see note 1) Number of chambers required 103 102.03 before rounding excess storage volume 0.9 % Number of chambers proposed 104 excess storage volume 1.9 % equal to (see note 2) 132 ft3 excess storage volume Installed chamber footprint (per chamber) = 5' x 7.12' Note: add 2' min. to each row, for end caps Storage Volume Provided = 7,084 ft3 Notes: 1. Storage volume assumes 6" of stone above and between chambers, and 40% stone porosity. Bozeman Public Safety Center Sub-Basin D1.12 (ST2) Storage Calculations (10-yr storm) StormTech Sizing Calculations Total required storage 4,763 ft3 Subtract surface retention -2,450 Required Storage Volume 2,313 ft3 StormTech Modules, Model No. SC740 (30" chamber height) Depth to top of gravel 36 in. installed storage volume 68.14 ft3 per chamber (see note 1) Number of chambers required 34 33.95 before rounding excess storage volume 0.1 % Number of chambers proposed 42 excess storage volume 19.2 % equal to (see note 2) 443 ft3 excess storage volume Installed chamber footprint (per chamber) = 5' x 7.12' Note: add 2' min. to each row, for end caps Storage Volume Provided = 2,757 ft3 Notes: 1. Storage volume assumes 6" of stone above and between chambers, and 40% stone porosity. Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.60 % Normal Depth 1.00 ft Diameter 12.00 in Discharge 2.99 ft³/s Results Discharge 2.99 ft³/s Normal Depth 1.00 ft Flow Area 0.79 ft² Wetted Perimeter 3.14 ft Hydraulic Radius 0.25 ft Top Width 0.00 ft Critical Depth 0.74 ft Percent Full 100.0 % Critical Slope 0.00742 ft/ft Velocity 3.81 ft/s Velocity Head 0.23 ft Specific Energy 1.23 ft Froude Number 0.00 Maximum Discharge 3.22 ft³/s Discharge Full 2.99 ft³/s Slope Full 0.00600 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 12" PVC - capacity at 0.60% 12/16/2019 9:49:04 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.60 % Normal Depth 1.25 ft Diameter 15.00 in Discharge 5.42 ft³/s Results Discharge 5.42 ft³/s Normal Depth 1.25 ft Flow Area 1.23 ft² Wetted Perimeter 3.93 ft Hydraulic Radius 0.31 ft Top Width 0.00 ft Critical Depth 0.94 ft Percent Full 100.0 % Critical Slope 0.00711 ft/ft Velocity 4.42 ft/s Velocity Head 0.30 ft Specific Energy 1.55 ft Froude Number 0.00 Maximum Discharge 5.83 ft³/s Discharge Full 5.42 ft³/s Slope Full 0.00600 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 15" PVC - capacity at 0.60% 12/16/2019 9:50:36 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Culvert Calculator Report SDMH#4 TO SDMH#3 Title: Bozeman Public Safety Center n:\2200\045\04 design\civil\drainage\pipes.cvm 08/15/20 09:17:52 PM Morrison Maierle Inc © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666 Project Engineer: MHickman CulvertMaster v3.3 [03.03.00.04] Page 1 of 1 Solve For: Headwater Elevation Culvert Summary Allowable HW Elevation 59.00 ft Headwater Depth/Height 2.90 Computed Headwater Eleva 58.51 ft Discharge 6.57 cfs Inlet Control HW Elev. 57.00 ft Tailwater Elevation 57.00 ft Outlet Control HW Elev. 58.51 ft Control Type Outlet Control Grades Upstream Invert 54.89 ft Downstream Invert 54.00 ft Length 111.00 ft Constructed Slope 0.008018 ft/ft Hydraulic Profile Profile PressureProfile Depth, Downstream 3.00 ft Slope Type N/A Normal Depth 1.09 ft Flow Regime N/A Critical Depth 1.03 ft Velocity Downstream 5.35 ft/s Critical Slope 0.008702 ft/ft Section Section Shape Circular Mannings Coefficient 0.012 Section MaterialCorrugated HDPE (Smooth Interior) Span 1.25 ft Section Size 15 inch Rise 1.25 ft Number Sections 1 Outlet Control Properties Outlet Control HW Elev. 58.51 ft Upstream Velocity Head 0.45 ft Ke 0.20 Entrance Loss 0.09 ft Inlet Control Properties Inlet Control HW Elev. 57.00 ft Flow Control Submerged Inlet Type Beveled ring, 33.7° bevels Area Full 1.2 ft² K 0.00180 HDS 5 Chart 3 M 2.50000 HDS 5 Scale B C 0.02430 Equation Form 1 Y 0.83000 Bozeman Public Safety Center Dry Well Storage Volume *** Revised 8/17/19; added this sheet Description Dry Well #1 Dry Well #2 Dry Well #3 Rim/Grate Elevation 59.60 59.00 59.80 Estimated Max. Groundwater Elevation1 53.00 53.00 53.00 Total Storage Depth to 18" Below Finished Grade2 5.10 4.50 5.30 Storage Volume in Manhole cone section volume 23.56 23.56 23.56 barrel section, storage depth (cone section to max. GW) 1.60 1.00 1.80 barrel section volume 20.11 12.57 22.62 Storage Volume in Manhole3 43.67 36.13 46.18 Storage Volume in Rock Fill (Void Space) Total Volume Excluding Manhole4 3,581.18 3,581.18 3,581.18 Volume below max. GW 354.05 529.50 304.88 Volume above max. GW 3,227.13 3,051.68 3,276.30 Storage Volume in Rock Fill5 1,290.85 1,220.67 1,310.52 Total Available Retention Volume (Manhole plus Rock Fill) 1,334.52 1,256.80 1,356.70 Notes 1. High groundwater estimate is conservatively high. Groundwater elevation measured in April/May 2019 was approximately 50.5 at all three dry wells. 2. Total Storage Depth is from bottom of structure to 18" below finished grade, and includes "dead" storage below estimated maximum groundwater elevation (which will be subtracted out later), plus active/useable storage above this level. 3. Storage Volume in Manhole is the air volume within the concrete dry well structure, and above the estimated max. groundwater elevation. 4. Total Volume Excluding Manhole is the space taken up by the rock and void spaces, excluding the manhole to outside diameter, and above the estimated maximum groundwater elevation. Based on 8' square bottom of dry welll excavation and 11/2:1 side slopes. 5. Water storage volume in the washed rock backfill is the volume of void space in the backfill that is above the maximum estimated groundwater elevation based on a 40% void ratio. OOOTVEEEEEEEEEDYHDYH GGGSSSDDSSSDTFFEFFFTTTTTWVWVWVWVWVWVWVWVWVWVWVWVWVWVSEWER MAIN ANDSERVICES APPROXIMATENOT SURVEYEDTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPTPMWMWMWMWMWMWESES ES ES ES ESES ES ES ES ESDEWEWEWEWEWESDESDESDEWEWEWEWEW EW EW EW EW EW EW EW EW EW EW EW EWESESESESESESESES476047594758 4761 4762 47634764476 54766 4 7 6 7 4760 47584756FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2019 N:\2200\045\ACAD\Civil\Exhibits\2200-045_STORM DRAIN DRAINAGE BASINS.dwg Plotted by mike g. hickman on Dec/16/2019 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 2200.045 1 DS BOZEMAN MONTANA PRE-DEVELOPMENT DRAINAGE MAP MGH BOZEMAN PUBLIC SAFETY CENTER MGH 12/2019 40 800 SCALE IN FEET LEGEND HX.X X.XX BASIN BOUNDARY SUB-BASIN BOUNDARY PRE-DEVELOPMENT SUB-BASIN DESIGNATION SUB-BASIN AREA (ACRES) STREAM>>>H2 0.29 H3 0.93 H1 6.26 H4 0.40 ESESESESESESESESES EWEWEWEWEWEWESDESDESDEWEWEWEWEWEWEWEWEWEWEWEWEWEWEWEWESESESES ES ES ES ESES OOOTVEEEEEEEEEDYHDYH GGGSSSDDSSSDTFFEFFFETTTTTWVWVWVWVWVWVWVWVWVWVWVWVWVWVOOOOOOOO O O O OO O E44+0045+0046+0047+0048+0049+0050+0051+0052+0053+0054+0055+0056+00PI: 54+95.1212SD SD SD SD SD SD SD SDSDSD SD SDS15SD15SD15SD15SD6SDDYHNGNGNGNGNGNGNGNGNGNGNGBPBPBPBPBPBPBPBPBPBPBPBPGBFBFBFBFBFBFBF6SD44+0045+0046+0047+0048+0049+0050+0051+0052+0053+0054+0055+0056+00PI: 54+95.1247654766476347684766 47 6 5 4763 4 7 6 0 47604761476347624759476 047634768477047574757 FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2020 N:\2200\045\ACAD\Civil\Exhibits\2200-045_STORM DRAIN DRAINAGE BASINS.dwg Plotted by mike g. hickman on Mar/13/2020 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 2200.045 2 DS BOZEMAN MONTANA POST-DEVELOPMENT DRAINAGE MAP MGH BOZEMAN PUBLIC SAFETY CENTER MGH 12/2019 LEGEND SUB-BASIN BOUNDARY POST-DEVELOPMENT SUB-BASIN DESIGNATION SUB-BASIN AREA (ACRES) UNDERGROUND STORAGE FACILITY (RETENTION / DETENTION) BASIN BOUNDARY STORM DRAIN PIPES, IN MODEL STORM DRAIN PIPES, NOT IN MODEL STREAM>>>P5 P9 NP4-1det C0NSTRUCTED 10-YR DETENTION PONDS (SEE TABLE 1) XX XX.X SURFACE RETENTIONS.R. 40 800 SCALE IN FEET D1.14 0.55 D2 0.15 D4 0.02 D3.1 0.09 GALLATIN COUNTY FAIRGROUNDS NORTH ROUSE AVE.EAST TAMARACK ST.EAST OAK ST.D3.3 0.07 D1.13B 0.24 D1.12 2.29 D1.13A 0.22 D1.11 1.53 D3.2 0.05 D1.7 0.50 D1.10 0.35 D1.9 0.52 D1.3 0.18 D1.2 0.17 D1.6 0.22 D1.5 0.09 D1.8 0.25 D1.1 0.15 D1.4 0.24 Bozeman Public Safety Center Storm Water Maintenance Plan August 17, 2020 The Bozeman Public Safety Center has a site-wide storm drainage system that will treat, store and convey storm and snowmelt runoff through the site to on-site retention storage facilities, with overflow provided for storms exceeding City of Bozeman retention requirements. Typically, runoff collects in paved areas and flows either directly to above-ground retention basins, to dry wells, or to the piped drainage system (storm drain) through curb inlets, drop inlets, manholes and culverts. The storm drain system discharges to one of two constructed underground detention and treatment facilities. The Bozeman Public Safety Center storm drain system is owned and operated by the City of Bozeman and includes all storm drain and surface water treatment and conveyance facilities within the property. The City of Bozeman will maintain the storm drainage system in accordance with this maintenance plan and with the applicable City of Bozeman regulations, and will maintain a written account of all maintenance and repair activities, such as a log book, for future reference. Every Month, May through October 1. Grass Swales (Lawns): Mow to maintain maximum grass height of 6 inches. Do not allow mulch to discharge or accumulate within 6 feet of the flowline. 2. Storm Drain Pipe and Culverts: Trim and control vegetation near open ends of pipes, to prevent any significant restriction of flow. 3. Surface Retention/Infiltration Facilities: Clean the area to keep free of leaves, grass clippings, excess vegetation and debris (paper, cardboard, plastic bags, etc.). If the basin contains water at the time of inspection, return later to clean the area. Every Three Months, and Immediately after Major Storm or Snowmelt Events 1. Grass Swales (Lawns and Native Grasses): Walk along each swale to inspect. Clean as needed to keep free of silt, debris, excess vegetation, or any other material that impedes flow. Note areas of ponding and areas with dense weeds or sparse grass cover, and repair within 1 year (see “Repair Procedures” below). 2. Storm Water Manholes and Inlets: Inspect each inlet grate and grated manhole cover. Clean as needed to keep free of leaves, debris, excess vegetation, or any other material (paper, cardboard, plastic bags, etc.) that impedes flow. In winter, ice or snow may remain over inlet grate. If water ponds excessively and creates a problem during snowmelt events, chip ice to provide a drainage channel into the manhole or inlet. 3. Surface Retention/Infiltration Facilities: From November through April, continue inspection and cleaning procedures as stated under the “monthly inspection” category above, every three months and immediately after major storm or snowmelt events. 4. Underground Retention/Infiltration Facilities: Open inspection port(s) in the isolator row, and view with a flashlight. If the geotextile fabric (at the bottom of the chamber) is obscured by sediment, measure depth to sediment level, and subtract from baseline depth (full depth to geotextile fabric). If the result (sediment level) is greater than 3 inches, schedule to have sediment removed, as stated under the “annual inspection” category below. Annually 1. Storm Drain Pipe (pipe terminating in manhole or inlet): Pull inlet grates and manhole covers as needed, and inspect each end of each pipe. If observed sediment level in the sump is above the lowest (discharge) pipe flowline, clean all sediment from the pipes and the manhole or inlet sump. 2. Storm Drain Pipe or Culvert (pipe terminating in open ditch or swale): If sediment has accumulated to 3 inches or more above the pipe flowline, remove sediment from the outlet pipe and ditch to provide free drainage and re-seed or sod the area of disturbance. If soil has eroded and un-vegetated rills are visible, re-seed or sod the area. If there are recurring problem areas, repair as stated in “Repair Procedures” below. 3. Underground Retention/Infiltration Facilities: Remove manhole covers leading to the isolator row. If the observed sediment level is above the lowest pipe flowline, clean all sediment from the pipes and the manhole or inlet sump. Also, look down the isolator row to see if sediment level is at or above the lower row of sidewall holes (about 3 inches above the geotextile bottom). Follow OSHA regulations for confined space entry, or use pole-mounted mirrors or cameras. If this observation or previous inspections through the inspection ports noted sediment levels greater than 3 inches, employ a pipe cleaning service to remove all sediment from the isolator row in accordance with the detention system manufacturer’s recommendations. Every 5 years 1. Surface Retention/Infiltration Facilities: Sediment, windblown dust and thatch will build up over time and reduce the storage capacity. Storage capacity is the basin’s airspace volume below the top of the point of overflow. Employ a land surveyor or engineer to determine the airspace volume. If it is less than the minimum volume indicated on the approved construction drawings (record drawings), remove excess material and replace landscape materials to originally constructed conditions. Repair Procedures 1. Grass Swales with Dense Weeds or Sparse Grass Cover: Re-seed or sod the area, but first determine and address the source of the problem. Expand irrigation coverage, add soil amendments, fertilize, etc., as needed to improve growth media and grass health, and to control weeds. 2. Grass Swales, Areas of Ponding: Cut sod and re-grade the area for consistent downgradient slope along the swale. Then re-seed or sod the area of disturbance. 3. Pipe Outlet Ditch, Excessive Sediment Accumulation: Cut sod, remove sediment, and re-grade the area to a consistent downgradient slope along the outlet ditch or swale. Extend the re-grading as far as needed to provide positive drainage. Then re-seed or re-sod the area of disturbance. 4. Pipe Outlet Ditch, Erosion: It is recommended to hire a Professional Engineer to address this issue. Another option is to cut sod and re-grade the area, install a permanent, non-degradable turf reinforcement mat (TRM) per the manufacturer’s recommendations, and re-seed the area of disturbance through the TRM per the manufacturer’s recommendations.