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HomeMy WebLinkAbout(27) Storm Drainage Report And Plan 5-14-21 Page 2 of 4   Lots 7 and 8. Sub-basin D1.2 will drain to an onsite surface retention basin located southwest of Lot 15. Runoff from Sub-basins D1.3 and D2 cannot be intercepted onsite; these areas will drain offsite as sheet flow over native vegetation to provide filtration, sediment capture, infiltration and nutrient uptake. For all areas of development, vegetated swales and sheet flow through re-graded and revegetated areas will provide opportunities for uptake of nutrients and other treatment processes. Sub-basins are listed on the “Peak Runoff Calculations” table in the attached calculations. 4 Retention and Detention Runoff from Sub-basin D1.1 will drain to a StormTech pre-fabricated underground treatment, storage and infiltration system located between Lots 7 and 8. This facility will include an inlet manhole that doubles as access for cleaning the isolator (sediment accumulation) row of the system. In a 10-year or smaller storm runoff event, all runoff will be routed through the StormTech system, and will discharge through a control structure. Bypass piping is provided for underground conveyance of storm runoff in excess of the 10-year design storm. The bottom of the stormwater storage for Sub-basin D1.1 will be at elevation 4703.50. The proposed detention basin is located between two on-site groundwater monitoring wells. Data was collected for these wells in April through July of 2015 and 2020. Based on the highest reading of both wells (4703.07), the detention storage volume is entirely above measured seasonal high groundwater elevation by 0.43 feet. Runoff from Sub-basin D1.2 will be retained onsite. The retention volume was calculated using the standard calculation in the City of Bozeman Design Standards. Side slopes will vary for a natural, rounded appearance, with maximum side slopes of 4:1 horizontal to vertical and a maximum depth to overflow of 1.0 feet. An overflow weir with vegetated slope protection will be constructed on the west retention berm, to pass runoff in excess of the required retention capacity. The bottom of the retention basin will be at elevation 4706.0, which is above the measured seasonal high groundwater elevation of 4705.60 (two years of data). System parameters and proposed structure elevations are summarized below. TABLE 1 - Detention and Retention Basin Data Description Detention (D1.1) Retention (D1.2) Max. 10-yr Release Rate (cfs) 0.61 0.00 10-yr Detention Volume (cu. ft.) 2,524 856 Sizes and Dimensions: vertical tee (riser) dia., inches 12 - outlet pipe dia., inches 12 - overflow weir length, ft. - 6 Orifice (two alternates): circular orifice dia., inches 35/8 - rectangular orifice, inches 31/4 x 31/4 - Elevations:  bottom of retention storage  bottom of detention storage  top of riser (= 10-yr max. WSEL)  25-yr WSEL at control structure  weir crest elevation 4706.00 4703.50 4706.50 4707.26 - 4706.00 - - 4707.20 4707.00 Page 3 of 4   Detention volume and pipe sizing calculations are attached. Design details will be provided on the construction drawings. 4 Storm Water Treatment The City’s design standards require Low Impact Development (LID) practices that infiltrate, evapotranspire or capture runoff, to the extent feasible, for a specified design runoff event. This requirement is addressed on the Bridger Meadows project by collecting runoff from all currently proposed impervious areas, and from all future improvements on the single-family lots to the extent feasible. Building design guidelines, enforced by the Property Owners Association, will include a requirement, enforced in the covenants, for each individual lot owner to route their roof drainage to rain barrels or on-site infiltration facilities, or to surface drain the runoff to the front side of the lot where it will collect in the street (this does not apply to Lots 15 and 16, which will drain to the surface retention basin). The site will be graded to make this feasible for each lot. The proposed detention and retention facilities are sized to accommodate any and all lots that route their roof runoff to the street; any lots utilizing on-site runoff storage will result in excess storage capacity, and improved storm water treatment. Direct runoff sub-basins D2 and D1.3 include back yard areas of several residential lots. Storm runoff from top of slope areas likely to be planted with lawn and other non-native plantings will drain as sheet flow over a steep slope vegetated with native grasses. The 15 to 30 feet of native vegetation will intercept, filter and infiltrate the small amount of runoff from the highly pervious back yards, making for an effective buffer to protect the undeveloped floodplain and wetland areas from sediment and nutrients. All street runoff, including the emergency access, will drain to an underground treatment and detention facility within sub-basin D1.1, or to a retention facility within sub-basin D1.2. The retention facility will treat the runoff through infiltration. The underground facility is described below. The proposed StormTech underground detention and storage facility will combine infiltration, runoff capture, treatment, and detention. The StormTech system is a widely accepted LID practice found to remove 80 percent of total suspended solids from municipal storm runoff. It meets LEED criteria for storm water treatment (SS6.2 water quality credit). The facility for this project will provide over 6 inches of capture depth for infiltration and runoff volume reduction, plus treatment of additional runoff by deposition as water slowly travels through the chambers and gravel base. The system solves the problem of runoff “short-circuiting” from inlet to outlet that is inherent in surface detention ponds. Runoff from the first ½” of rainfall will percolate through and fill a gravel filter before finding its way to a perforated low-flow outlet pipe that discharges into the detention outlet control structure. Additional runoff from larger storms can bypass this discharge route, but only after storage depth reaches 2 feet. Although the detention calculations assume zero infiltration, infiltration will further improve treatment capabilities in the most common, smaller storm events. We believe this type of treatment not only meets, but exceeds, the City’s current design standards. Page 4 of 4   5 Conveyance The storm drain system is sized for collection and underground conveyance of the 25-year peak runoff. Overland conveyance of excess runoff from larger, less frequent storms will be incorporated into the site grading. The table below summarizes the storm drain pipe sizes required to convey the 25-year peak runoff. 12” pipe will cross Shady Glen Lane, 15” pipe will run from the west curb inlet to the underground detention facility, and the discharge pipe from the underground detention facility will be a 12” pipe. Sub-basin Name 25-year Peak Runoff (cfs) Pipe Info Diameter (ft.) Min. Slope (%) Capacity (cfs) D1.1 5.17 12” 2.00 5.46 D1.1 5.17 15” 0.60 5.42 Supporting calculations are attached. Design details will be provided on the construction drawings.    CALCULATIONS    (this page left blank intentionally) Bridger Meadows Peak Runoff Calculations 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 4.13 0.20 9.08 0.92 1.44 1.80 2.16 2.64 2.96 D1.1 (det.) 2.75 0.66 7.97 2.20 3.44 4.33 5.17 6.35 7.11 5,373 D1.2 (ret.) 0.64 0.45 5.00 0.46 0.74 0.93 1.11 1.38 1.55 856 D1.3 (direct) 1.43 0.26 5.00 0.59 0.95 1.19 1.42 1.76 1.98 1,096 Basin 2 H2 1.00 0.20 10.67 0.20 0.31 0.39 0.47 0.58 0.64 D2 (direct) 0.31 0.29 5.00 0.15 0.23 0.29 0.35 0.43 0.49 Bridger Meadows Runoff Coefficients (Rational Method) Area Area (sq. ft.) Runoff INPUT Sub-Basin (acres) Total Pervious Impervious Coefficient Pervious Impervious Basin 1 H1 4.13 179,903 179,903 0 0.20 D1.1 (det.) 2.75 119,790 40,756 79,034 0.66 79,034 D1.2 (ret.) 0.64 27,878 17,798 10,080 0.45 10,080 D1.3 (direct) 1.43 62,291 56,991 5,300 0.26 5,300 Basin 2 H2 1.00 43,560 43,560 0 0.20 D2 (direct) 0.31 13,504 11,704 1,800 0.29 1,800 Time of Concentration Record Id: H1 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Short prairie grass and lawns. 0.15 42.00 ft 2.4% 0.15 1.20 in 7.431 min Int Channel Grassed (n=0.030) 250.00 ft 2.2% 0.03 1.6538 min Pervious TC 9.0848 min   Record Id: H2 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Short prairie grass and lawns. 0.15 44.00 ft 1.1% 0.15 1.20 in 10.5375 min Shallow High grass (n=0.035) 22.00 ft 9.1% 0.035 0.1325 min Pervious TC 10.67 min   Record Id: D1-1 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Short prairie grass and lawns. 0.15 20.00 ft 1.0% 0.15 1.20 in 5.8258 min Int Channel Grassed (n=0.030) 80.00 ft 2.0% 0.03 0.5551 min Int Channel concrete curb & gutter 425.00 ft 1.3% 0.013 1.5849 min Pervious TC 7.9658 min   NOTE: The minimum time of concentration (5 minutes) was used for all other post-development drainage basins. Bridger Meadows Sub-Basin D1.1 Detention (10-yr storm) MODIFIED RATIONAL METHOD Qp = C i A POST-DEVELOPMENT PRE-DEVEL. 2.75 AC Qp (Basin H1) = 1.80 cfs Direct Runoff (Basin D1.3) = 1.19 cfs 0.66 0.61 8.0 MIN D1.1 release rate = 0.61 cfs 2.38 IN/HR TIME STEP 4.33 CFS DURATION = 5.0 min. Max. Volume, Max. Volume,Required Detention Triangle Rel. (cu. ft.) Constant Rel. (cu. ft.)Volume (cu. ft.) 3043.02 2004.09 2,524 Triangle Release Constant Release DURATION INTENSITY Qp POND VOLUME POND VOLUME (MIN) (IN/HR) (CFS) (CF) (CF) 7.57 2.46 4.47 1,748 1,504 15.54 1.54 2.80 2,184 1,817 23.51 1.18 2.14 2,446 1,953 31.48 0.97 1.77 2,625 2,004 ORIFICE CALCULATIONS 39.45 0.84 1.53 2,754 2,004 MATCHING Qp = 0.61 cfs 47.42 0.75 1.36 2,850 1,968 Max. Depth = 3.00 ft 55.39 0.67 1.23 2,920 1,906 63.36 0.62 1.12 2,970 1,824 71.33 0.57 1.04 3,006 1,727 79.30 0.53 0.97 3,028 1,616 CIRCULAR ORIFICE: 87.27 0.50 0.91 3,040 1,494 DIAMETER = 3.6250 inches 95.24 0.47 0.86 3,043 1,362 Area = 0.07 ft 2 103.21 0.45 0.82 3,038 1,223 ORIFICE FLOW = 0.60 CFS 111.18 0.43 0.78 3,026 1,076 119.15 0.41 0.75 3,008 922 127.12 0.39 0.72 2,985 764 RECTANGULAR ORIFICE: 135.09 0.38 0.69 2,956 600 LENGTH = 3.250 inches 143.06 0.36 0.66 2,923 431 WIDTH = 3.250 inches 151.03 0.35 0.64 2,887 258 Area = 0.07 ft 2 159.00 0.34 0.62 2,846 81 ORIFICE FLOW = 0.61 CFS 166.97 0.33 0.60 2,802 -99 174.94 0.32 0.58 2,755 -282 182.91 0.31 0.56 2,705 -469 190.88 0.30 0.55 2,653 -658 198.85 0.29 0.53 2,598 -850 WEIR CALCULATIONS (not used) 206.82 0.29 0.52 2,541 -1,045 Coefficient = 3.33 214.79 0.28 0.51 2,481 -1,241 Width = 0.4063 inches 222.76 0.27 0.50 2,420 -1,440 WEIR FLOW = 0.59 CFS 230.73 0.27 0.49 2,356 -1,641 238.70 0.26 0.47 2,291 -1,844 246.67 0.26 0.46 2,224 -2,049 POST-DEV Qp = POND VOLUME CALCULATIONS: BASIN AREA POST = POST-DEV Tc = POST-DEV C = STORM INTENSITY = DURATION INTENSITY Qp POND VOLUME POND VOLUME (MIN) (IN/HR) (CFS) (CF) (CF) 254.64 0.25 0.46 2,155 -2,255 262.61 0.25 0.45 2,085 -2,463 270.58 0.24 0.44 2,013 -2,673 278.55 0.24 0.43 1,940 -2,884 286.52 0.23 0.42 1,865 -3,096 294.49 0.23 0.41 1,790 -3,310 302.46 0.22 0.41 1,713 -3,525 310.43 0.22 0.40 1,635 -3,742 318.40 0.22 0.39 1,555 -3,959 326.37 0.21 0.39 1,475 -4,178 334.34 0.21 0.38 1,394 -4,398 342.31 0.21 0.38 1,311 -4,619 350.28 0.20 0.37 1,228 -4,840 358.25 0.20 0.36 1,144 -5,063 366.22 0.20 0.36 1,059 -5,287 374.19 0.19 0.35 973 -5,512 382.16 0.19 0.35 886 -5,737 390.13 0.19 0.34 798 -5,963 398.10 0.19 0.34 710 -6,191 406.07 0.18 0.34 621 -6,419 414.04 0.18 0.33 531 -6,647 422.01 0.18 0.33 441 -6,877 429.98 0.18 0.32 350 -7,107 437.95 0.18 0.32 258 -7,338 445.92 0.17 0.32 165 -7,569 453.89 0.17 0.31 72 -7,802 461.86 0.17 0.31 -21 -8,035 469.83 0.17 0.31 -115 -8,268 477.80 0.17 0.30 -210 -8,502 485.77 0.16 0.30 -306 -8,737 493.74 0.16 0.30 -401 -8,972 501.71 0.16 0.29 -498 -9,208 509.68 0.16 0.29 -595 -9,444 517.65 0.16 0.29 -692 -9,681 525.62 0.16 0.28 -790 -9,918 533.59 0.15 0.28 -888 -10,156 541.56 0.15 0.28 -987 -10,395 549.53 0.15 0.28 -1,086 -10,633 557.50 0.15 0.27 -1,186 -10,873 565.47 0.15 0.27 -1,286 -11,113 573.44 0.15 0.27 -1,387 -11,353 581.41 0.15 0.27 -1,488 -11,593 589.38 0.14 0.26 -1,589 -11,834 597.35 0.14 0.26 -1,691 -12,076 605.32 0.14 0.26 -1,793 -12,318 613.29 0.14 0.26 -1,895 -12,560 621.26 0.14 0.25 -1,998 -12,803 629.23 0.14 0.25 -2,101 -13,046 637.20 0.14 0.25 -2,205 -13,289 645.17 0.14 0.25 -2,309 -13,533 653.14 0.14 0.25 -2,413 -13,777 661.11 0.13 0.24 -2,517 -14,022 669.08 0.13 0.24 -2,622 -14,267 677.05 0.13 0.24 -2,727 -14,512 685.02 0.13 0.24 -2,833 -14,757 692.99 0.13 0.24 -2,939 -15,003 700.96 0.13 0.24 -3,045 -15,249 708.93 0.13 0.23 -3,151 -15,496 716.90 0.13 0.23 -3,258 -15,743 724.87 0.13 0.23 -3,365 -15,990 732.84 0.13 0.23 -3,472 -16,237 740.81 0.12 0.23 -3,579 -16,485 Bridger Meadows Sub-Basin D1.1 Storage Calculations (10-yr storm) StormTech Sizing Calculations Required Storage Volume 2,524 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 38 37.03 before rounding (see note 2) excess storage volume 2.5 % Number of chambers proposed 36 MH storage 38 (two 4' dia. Manholes at 3' water depth) Overflow Pipe storage 126 (40' of 12" pipe) Total Storage 2,616 ft3 excess storage volume 92.8 ft3 equal to 3.68 % 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 = 2,616 ft3 Notes: 1. Storage volume assumes 6" of stone above and between chambers, and 40% stone porosity. 2. "Number of chambers required" does not account for additional storage available in manholes, pipes and excess washed rock backfill. Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 2.00 % Normal Depth 1.00 ft Diameter 12.00 in Discharge 5.46 ft³/s Results Discharge 5.46 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 0.94 ft Percent Full 100.0 % Critical Slope 0.01728 ft/ft Velocity 6.95 ft/s Velocity Head 0.75 ft Specific Energy 1.75 ft Froude Number 0.00 Maximum Discharge 5.87 ft³/s Discharge Full 5.46 ft³/s Slope Full 0.02000 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" HDPE 8/7/2020 9:47:14 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" HDPE 8/7/2020 9:48:30 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 47024703 4704470047044706 47074708 470347034704 4702 4 7 0 2 4702 4 7 0 4 470547074710 4713470647114712471147094708470547054701470 1 47004699 [][]GWGWGWGWGWGWGWGW GWVILLAGE CREEKTOWNHOUSESTHE LINKS CONDOMINIUMS BRIDGER CENTER SUBDIVISION B O Y L A N R O A D FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2021 N:\5311\001.01 - PUD\ACAD\Exhibits\5311-001_STORM DRAIN DRAINAGE BASINS (PRE).dwg Plotted by cody farley on Feb/24/2021 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 2200.045 1 CJF BOZEMAN MONTANA PRE-DEVELOPMENT DRAINAGE MAP MGH BRIDGER MEADOWS MGH 07/2020 50 1000 SCALE IN FEET LEGEND HX.X X.XX BASIN BOUNDARY SUB-BASIN BOUNDARY PRE-DEVELOPMENT SUB-BASIN DESIGNATION SUB-BASIN AREA (ACRES) DITCH>>>H1 4.13 H2 1.00 47024703 4704470047044706 47074708 470347034704 4702 4 7 0 2 4702 4 7 0 4 47054707471 0 47134706471147124711470947084705470547014701 47004699 [][]GWGWGWGWGWGWGWGWGW12SDWVWV CP BF C VIL LAGE CREEKTOWNHOUSESTHE LINKS CONDOMINIUMS >>>>>>>>>>BRIDGER CENTER SUBDIVISION47094708 4708 471 0 47 1 3 47 1 047054705 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 DITCH>>>P5 P9 NP4-1det C0NSTRUCTED 10-YR DETENTION PONDS (SEE TABLE 1) XX XX.X SURFACE RETENTIONS.R. 50 1000 SCALE IN FEETSHADY GLEN LANE B O Y L A N R O A D D1.3 1.43 D1.1 2.75 D1.2 0.64 D2 0.31 LOT 1 LOT 2LOT 3 LOT 4 LOT 5 LOT 6 LOT 7 LOT 8 LOT 9 LOT 10 LOT 11 LOT 12 LOT 13 LOT 14 LOT 15 LOT 16 O.S. 01 O.S. 02 O.S. 03 O.S. 04 O.S. 05 SURFACE RETENTION BASIN UNDERGROUND DETENTION FACILITY FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2021 N:\5311\001.01 - PUD\ACAD\Exhibits\5311-001_STORM DRAIN DRAINAGE BASINS (POST).dwg Plotted by dean squires on May/14/2021 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 2200.045 2 CJF BOZEMAN MONTANA POST-DEVELOPMENT DRAINAGE MAP MGH BRIDGER MEADOWS MGH 07/2020