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HomeMy WebLinkAbout019 - Appendix O - Drainage Report MEADOW BRIDGE SUBDIVISION PRELIMINARY DRAINAGE REPORT Project # BOZ_05021.28 Bozeman, MT APRIL 2025 April 2025 Project No. 05021.28 PRELIMINARY DRAINAGE REPORT MEADOW BRIDGE SUBDIVISION BOZEMAN, MONTANA 59715 SITE NARRATIVE The purpose of this drainage report is to present a summary of calculations to quantify the stormwater runoff for the Meadow Bridge Subdivision project. All design criteria and calculations are in accordance with The City of Bozeman Design Standards and Specifications Policy, dated October 2024. Site stormwater improvements have been designed with the intent to meet the current drainage regulations for the City of Bozeman. LOCATION The development site is located on the north side of Blackwood Road, west of South 23rd Street and east of Parkway Avenue in Bozeman, Montana. The legal description for the lot is: certificate of survey no. 2286, excepting therefrom Meadow Creek Subdivision Phase 1, situated in the W1/2SE1/4 of Section 23, T02 S, R05 E in Bozeman, Montana. EXISTING SITE CONDITIONS The project site is 25.319 acres of currently undeveloped vacant grassland. Runoff is generally conveyed from south to north through the site towards a series of existing detention ponds that outflow to Middle Creek. The existing detention ponds were sized for development as part of the Meadow Creek and South Bridge Subdivisions. Refer to Meadow Creek Subdivision Phase II & III as-built plans and stormwater design report prepared by Engineering Inc., dated November 2008 and April 2006 respectively. Reference Appendix A for the existing watershed drainage basin figure. The existing detention facilities were designed and constructed to include a storage volume larger than the required capacity. A summary of the existing basin facilities is included in Table 1 below. Preliminary Drainage Report Page 2 of 5 April 2025 Table 1: Existing Detention Ponds Existing Drainage Basin Contributing Drainage Area (Acres) C Factor Required Storage (cu. ft.) Provided Storage (cu. ft.) Excess Storage (cu. ft.) 5B 3.09 0.35 1,258 1,479 221 6A 7.31 0.35 2,741 3,037 296 7 11.15 0.35 3,994 4,380 386 6B 0.4 0.60 174 353 179 Since the existing detention ponds are located adjacent to open space and Middle Creek, the proposed development will manage all new stormwater runoff by expanding the existing ponds. PROPOSED PROJECT The proposed improvements for the Meadow Bridge Subdivision will include roads, sidewalks, open space and 45 new residential lots with service connections to existing or proposed water and sanitary sewer infrastructure located within Blackwood Road, South 23rd Avenue, Last Loop Drive, Parkway Avenue, and proposed alleys. The existing detention ponds will be expanded to provide infiltration, treatment, and storage of stormwater runoff. The proposed area of development has been divided into four (4) total sub-basins as shown in Appendix B. Preliminary hydrologic calculations for each sub-basin are included in Appendix C of this report. Sub-basin A includes the proposed lots 1-12, the new paved alley, and sidewalk in the northwest corner of the development. Runoff will flow towards the new paved alley and the existing curb and gutter within Parkway Avenue and outfall to the existing detention pond 5B through an existing sidewalk chase. The storage capacity of the existing detention pond 5B will be increased to provide storage and infiltration of the storm runoff and to maintain the historic pre-development flow rate and flow path prior to outfall to Middle Creek. Sub-basin B includes the proposed lots 13-34 in the southwest half of the development. Runoff will flow towards Last Loop Drive where it will flow into the existing curb and gutter towards the sidewalk chase in Kurk Drive that outfalls to the existing detention pond 6A. The storage capacity of the existing detention pond 6A will also be increased to provide storage volume and to maintain the historic pre-development flow rate and flow path into Middle Creek through the existing outfall structure. Although development of Last Loop Drive and proposed lots 13-22 have not yet been completed, Preliminary Drainage Report Page 3 of 5 April 2025 these areas of development were previously included in the analysis of the current existing conditions. Sub-basin C includes the proposed lots 35-45 in the southeast corner of the development. Runoff from sub-basin C will flow towards the existing curb and gutter within South 23rd Avenue where it will then flow within the gutter towards the existing curb inlet where it will the flow within an existing 12-inch pipe to the existing detention pond 7. The storage volume of the existing detention pond 7 will be increased to accommodate the increase in runoff and to maintain the historic pre-development flow rate and flow path into Middle Creek through the existing outfall structure. Complete construction of Blackwood Road and South 23rd Avenue was included in the original analysis of detention pond 7 and therefore considered existing conditions. Sub-basin D includes the right-of-way area of the north side of Kurk Drive and east side of South 23rd Avenue. This area is currently developed with curb and gutter, sidewalk and pavement, as designed with the original developed conditions of Pond 6B. However, runoff flowing on the east side of South 23rd Avenue was originally designed to convey towards detention pond 12 as shown in Exhibit A of Appendix A. This portion of stormwater runoff will be re-routed via curb and gutter to flow towards the existing sidewalk chase and outfall to the existing detention pond 6B. The Rational method was used to calculate the additional storage volume required for each detention pond and each pond was designed assuming a dry detention pond. Per the latest City of Bozeman drainage regulations, if the bottom of a pond is within 2- feet of the seasonally high groundwater elevation, the pond must be designed as a wet pond. Based on the groundwater monitoring completed in 2024, Pond 5B will be designed as a wet pond. Table 2 below summarizes the proposed pond expansion volumes. Table 2: Detention Pond Storage Requirements Pre-Development Post-Development Basin Outfall Point Area (Acres) C Factor Pre-Dev Volume Required (ft3) Pre-Dev Storage Provided (cu. ft.) Area (Acres) C Factor Post-Dev Volume Required (ft3) Pond Volume Expansion (ft3) A Pond 5B 3.32 0.35 1,222 1,479 7.00 0.36 3,430 1,951 B Pond 6A 7.37 0.35 2,724 3,037 7.37 0.41 3,717 680 C Pond 7 9.45 0.35 3,071 4,380 10.43 0.39 3,146 0 D Pond 6B 0.40 0.60 178 353 1.67 0.32 404 51 Preliminary Drainage Report Page 4 of 5 April 2025 INLETS The existing inlets have been designed to capture runoff from the right-of-way area in accordance with The City of Bozeman Design Standards and Specifications Policy. Bentley’s FlowMaster software, which uses the FHWA HEC-22 Manual, will be used to confirm the existing spread width and the new gutter flow depth at each of the existing inlets using the calculated peak post-development flow rate from the 25-year storm event. The allowable limit for the depth of flow in the curb line is 0.15-feet below the top of curb. Existing inlets are assumed to have a 50 percent clogging factor for sag inlets. All inlets and manholes are assumed to have a nine (9) inch sump for sediment collection. Each existing detention pond includes an outfall structure that includes an orifice opening to limit the stormwater discharge. The orifice openings will control the increased runoff generated from the proposed development at the pre-development discharge flow rates provided in Appendix C. PIPES In order to maintain the existing discharge rate, the existing detention pond capacities will be increased while the outflow structures and discharge pipes remain the same. No new storm drain pipe is anticipated at this time. DETENTION BASIN FACILITIES As mentioned above, expansion to four existing detention ponds is proposed for this development. All detention ponds have been analyzed assuming an initial design for the ten (10) year storm intensity. A maximum side slope of 4:1 will be maintained for each detention pond and each will have a maximum water depth of one and a half feet with a maximum overall basin depth of two and a half feet. See Appendix C for the Preliminary Post-Development Hydrology Calculations. MAJOR STORM EVENTS In the event of a 100-year storm event, the detention basins will flow over the overflow weir in each outfall structure and flow towards Middle Creek as it has historically. Runoff within Parkway Avenue, Kurk Drive, Last Loop Drive, Blackwood Road and South 23rd Avenue will be contained within the existing curb and gutter and have channelized flow within the roadways until outfall through storm drain inlets or sidewalk chases. Preliminary Drainage Report Page 5 of 5 April 2025 WATER QUALITY The City of Bozeman Design Standards and Specifications Policy states the requirement to capture or reuse the runoff generated from the first 0.5 inches of rainfall from a 24- hour storm. We meet this requirement by capturing and detaining all runoff on-site in the proposed expanded detention ponds with outflow structures to limit the release rate to pre-development conditions. In addition to the expanded detention volume, the existing manhole sumps are included in the storm drain inlets prior to outflow, providing treatment before water is released to Middle Creek. Detention Pond 5B was designed as a wet pond in anticipation that seasonal high ground water will be less than 2-ft below the pond bottom. The wet pond was designed in accordance with the Montana Post-Construction Storm Water BMP Design Guidance Manual. All other detention ponds will have 2-ft of separation from the seasonal high groundwater to deter any degradation of groundwater. The stormwater detention systems need to be maintained, according to the recommendations in the Operations and Maintenance Manual, see Appendix D. CONCLUSION The preliminary drainage plan for the Meadow Bridge Subdivision project adheres to The City of Bozeman Design Standards and Specifications Policy, dated October 2024. Through comprehensive calculations and adherence to city regulations, the proposed stormwater system will effectively handle runoff within the area of development. The existing inlets, pipes, expanded detention ponds, and curb and gutter will all be utilized within the design. The proposed improvements aim to contribute positively to the development while assuring all designs are within city regulations. APPENDICES Appendix A - Exhibit A - Stormwater Pre-Development Basins Appendix B - Exhibit B - Stormwater Post-Development Basins Appendix C - Hydrology Calculations Appendix D - O&M Plan Appendix E – Geotechnical Report Appendix F - Groundwater Monitoring MEADOW BRDIGE SUBDIVISION Project # BOZ_05021.28 APPENDIX A EXHIBIT A – PRE-DEVELOPMENT BASIINS EXHIBIT A 100 50 0 SCALE:1" = 100' 100 200 MEADOW BRIDGE SUBDIVISION Project # BOZ_05021.28 APPENDIX B EXHIBIT B – POST-DEVELOPMENT BASINS EXHIBIT B 100 50 0 SCALE:1" = 100' 100 200 MEADOW BRIDGE SUBDIVISION Project # BOZ_05021.28 APPENDIX C HYDROLOGY CALCULATIONS Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =0.50 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 144568.98 3.319 0.35 1 0.35 0.35 1.16 0.00 0.00 0.00 1 0.00 0.00 0 1 0.00 0.00 0 1 0.00 0.00 0 144568.98 3.32 1.1616 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =1.16 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 10.64 2 5.84 6.78 3 4.49 5.21 4 3.72 4.32 5 3.22 3.74 10 2.05 2.38 15 1.58 1.83 20 1.31 1.52 25 1.13 1.31 30 1.00 1.17 35 0.91 1.06 40 0.83 0.97 45 0.77 0.90 50 0.72 0.84 55 0.68 0.79 60 0.64 0.74 75 0.55 0.64 90 0.49 0.57 105 0.44 0.52 120 0.41 0.47 150 0.35 0.41 180 0.31 0.36 1,221.99 ft3 1.52 (ft3/s) Residential RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN A - PRE-DEVELOPMENT CONDITIONS Surface Type Totals = 0.3500 Cwd x Cf =0.35 Runoff Volume Discharge Volume Site Detention = = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) 638.54 30.00 608.54 813.85 60.00 753.85 937.94 90.00 847.94 1037.30 120.00 917.30 1121.56 150.00 971.56 1429.50 300.00 1129.50 1647.47 450.00 1197.47 1821.99 600.00 1221.99 1969.99 750.00 1219.99 2099.80 900.00 1199.80 2216.20 1050.00 1166.20 2322.23 1200.00 1122.23 2419.97 1350.00 1069.97 2510.87 1500.00 1010.87 2596.04 1650.00 946.04 2676.32 1800.00 876.32 2893.72 2250.00 643.72 3084.39 2700.00 384.39 3255.38 3150.00 105.38 3411.13 3600.00 ----- 3688.22 4500.00 ----- 3931.25 5400.00 ----- = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =1.10 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 320848.09 7.366 0.35 1 0.35 0.35 2.58 1 0.00 0.00 0.00 1 0.00 0.00 0 1 0.00 0.00 0 1 0.00 0.00 0 320848.0902 7.37 2.5780 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =2.58 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 23.62 2 5.84 15.05 3 4.49 11.56 4 3.72 9.59 5 3.22 8.30 10 2.05 5.29 15 1.58 4.06 20 1.31 3.37 25 1.13 2.91 30 1.00 2.59 35 0.91 2.34 40 0.83 2.15 45 0.77 1.99 50 0.72 1.86 55 0.68 1.75 60 0.64 1.65 75 0.55 1.43 90 0.49 1.27 105 0.44 1.15 120 0.41 1.05 150 0.35 0.91 180 0.31 0.81 2,723.61 ft3 3.37 (ft3/s) Residential RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN B - PRE-DEVELOPMENT CONDITIONS Surface Type Totals = 0.3500 Cwd x Cf =0.35 Runoff Volume Discharge Volume Site Detention = = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) 1417.13 66.00 1351.13 1806.22 132.00 1674.22 2081.62 198.00 1883.62 2302.13 264.00 2038.13 2489.14 330.00 2159.14 3172.56 660.00 2512.56 3656.29 990.00 2666.29 4043.61 1320.00 2723.61 4372.08 1650.00 2722.08 4660.17 1980.00 2680.17 4918.50 2310.00 2608.50 5153.83 2640.00 2513.83 5370.73 2970.00 2400.73 5572.48 3300.00 2272.48 5761.51 3630.00 2131.51 5939.67 3960.00 1979.67 6422.15 4950.00 1472.15 6845.32 5940.00 905.32 7224.79 6930.00 294.79 7570.47 7920.00 ----- 8185.42 9900.00 ----- 8724.78 11880.00 ----- = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =1.80 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 411630.01 9.450 0.35 1 0.35 0.35 3.31 1 0.00 0.00 0.00 1 0.00 0.00 0 1 0.00 0.00 0 1 0.00 0.00 0 411630.01 9.45 3.3074 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =3.31 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 30.30 2 5.84 19.31 3 4.49 14.84 4 3.72 12.31 5 3.22 10.64 10 2.05 6.78 15 1.58 5.21 20 1.31 4.32 25 1.13 3.74 30 1.00 3.32 35 0.91 3.00 40 0.83 2.76 45 0.77 2.55 50 0.72 2.38 55 0.68 2.24 60 0.64 2.12 75 0.55 1.83 90 0.49 1.63 105 0.44 1.47 120 0.41 1.35 150 0.35 1.17 180 0.31 1.04 3,070.82 ft3 5.21 (ft3/s) 10501.44 16200.00 ----- 11193.40 19440.00 ----- 9269.00 11340.00 ----- 9712.48 12960.00 ----- 8239.26 8100.00 139.26 8782.17 9720.00 ----- 7391.69 5940.00 1451.69 7620.26 6480.00 1140.26 6890.35 4860.00 2030.35 7149.18 5400.00 1749.18 6310.16 3780.00 2530.16 6612.07 4320.00 2292.07 5609.13 2700.00 2909.13 5978.73 3240.00 2738.73 4690.82 1620.00 3070.82 5187.73 2160.00 3027.73 3193.42 540.00 2653.42 4070.21 1080.00 2990.21 2670.60 324.00 2346.60 2953.51 432.00 2521.51 1818.10 108.00 1710.10 2317.27 216.00 2101.27 = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) = 0.3500 Cwd x Cf =0.35 Runoff Volume Discharge Volume Site Detention = Totals Residential RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN C - PRE-DEVELOPMENT CONDITIONS Surface Type = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =0.20 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 17591.45 0.404 0.60 1 0.60 0.60 0.24 1 0.00 0.00 0.00 1 0.00 0.00 0 1 0.00 0.00 0 1 0.00 0.00 0 17591.45 0.40 0.2423 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =0.24 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 2.22 2 5.84 1.41 3 4.49 1.09 4 3.72 0.90 5 3.22 0.78 10 2.05 0.50 15 1.58 0.38 20 1.31 0.32 25 1.13 0.27 30 1.00 0.24 35 0.91 0.22 40 0.83 0.20 45 0.77 0.19 50 0.72 0.17 55 0.68 0.16 60 0.64 0.16 75 0.55 0.13 90 0.49 0.12 105 0.44 0.11 120 0.41 0.10 150 0.35 0.09 180 0.31 0.08 178.19 ft3 0.50 (ft3/s) Right-of-way RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN D - PRE-DEVELOPMENT CONDITIONS Surface Type Totals = 0.6000 Cwd x Cf =0.60 Runoff Volume Discharge Volume Site Detention = = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) 133.20 12.00 121.20 169.77 24.00 145.77 195.65 36.00 159.65 216.38 48.00 168.38 233.96 60.00 173.96 298.19 120.00 178.19 343.66 180.00 163.66 380.06 240.00 140.06 410.94 300.00 110.94 438.01 360.00 78.01 462.29 420.00 42.29 484.41 480.00 4.41 504.80 540.00 ----- 523.76 600.00 ----- 541.53 660.00 ----- 558.27 720.00 ----- 603.62 900.00 ----- 643.40 1080.00 ----- 679.06 1260.00 ----- 711.55 1440.00 ----- 769.35 1800.00 ----- 820.05 2160.00 ----- = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =0.50 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 144568.98 3.319 0.35 1 0.35 0.35 1.162 14099.08 0.324 0.60 1 0.60 0.60 0.194 126785.16 2.911 0.35 1 0.35 0.35 1.019 19618.91 0.450 0.20 1 0.20 0.20 0.090 305072.13 7.00 2.465 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =2.27 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 20.80 2 5.84 13.26 3 4.49 10.18 4 3.72 8.45 5 3.22 7.31 10 2.05 4.66 15 1.58 3.58 20 1.31 2.97 25 1.13 2.57 30 1.00 2.28 35 0.91 2.06 40 0.83 1.89 45 0.77 1.75 50 0.72 1.64 55 0.68 1.54 60 0.64 1.45 75 0.55 1.26 90 0.49 1.12 105 0.44 1.01 120 0.41 0.93 150 0.35 0.80 180 0.31 0.71 3,430.95 ft3 1.45 (ft3/s) 7208.75 4500.00 2708.75 7683.75 5400.00 2283.75 6362.74 3150.00 3212.74 6667.17 3600.00 3067.17 5655.87 2250.00 3405.87 6028.55 2700.00 3328.55 5074.05 1650.00 3424.05 5230.95 1800.00 3430.95 4729.90 1350.00 3379.90 4907.58 1500.00 3407.58 4331.63 1050.00 3281.63 4538.88 1200.00 3338.88 3850.41 750.00 3100.41 4104.12 900.00 3204.12 3220.03 450.00 2770.03 3561.14 600.00 2961.14 2192.14 150.00 2042.14 2794.01 300.00 2494.01 1833.24 90.00 1743.24 2027.44 120.00 1907.44 1248.04 30.00 1218.04 1590.70 60.00 1530.70 = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) = 0.3242 Cwd x Cf =0.32 Runoff Volume Discharge Volume Site Detention Existing Residential Residential Open Space Totals = New Right-of-way RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN A - POST-DEVELOPMENT CONDITIONS Surface Type = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =1.10 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 320848.09 7.366 0.35 1 0.35 0.35 2.578 6215.18 0.143 0.60 1 0.60 0.60 0.086 71357.29 1.638 0.35 1 0.35 0.35 0.573 1 0.00 0.00 0 398420.55 9.15 3.237 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =3.15 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 28.87 2 5.84 18.40 3 4.49 14.14 4 3.72 11.73 5 3.22 10.14 10 2.05 6.46 15 1.58 4.97 20 1.31 4.12 25 1.13 3.56 30 1.00 3.16 35 0.91 2.86 40 0.83 2.63 45 0.77 2.43 50 0.72 2.27 55 0.68 2.13 60 0.64 2.02 75 0.55 1.74 90 0.49 1.55 105 0.44 1.40 120 0.41 1.29 150 0.35 1.11 180 0.31 0.99 3,716.60 ft3 3.16 (ft3/s) Existing Residential RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN B - POST-DEVELOPMENT CONDITIONS Surface Type = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume New Residential Totals = = 0.3445 Cwd x Cf =0.34 Runoff Volume Discharge Volume Site Detention (ft3) (ft 3) (ft 3) 1732.30 66.00 1666.30 2207.92 132.00 2075.92 2544.58 198.00 2346.58 2814.13 264.00 2550.13 3042.73 330.00 2712.73 3878.14 660.00 3218.14 4469.46 990.00 3479.46 4942.92 1320.00 3622.92 5344.44 1650.00 3694.44 5696.60 1980.00 3716.60 6012.39 2310.00 3702.39 6300.05 2640.00 3660.05 6565.20 2970.00 3595.20 6811.81 3300.00 3511.81 7042.88 3630.00 3412.88 7260.66 3960.00 3300.66 7850.45 4950.00 2900.45 New Right-of-way 10665.19 11880.00 ----- 9254.15 7920.00 1334.15 10005.88 9900.00 105.88 8367.74 5940.00 2427.74 8831.60 6930.00 1901.60 = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =1.80 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 411630.01 9.450 0.35 1 0.35 0.35 3.307 31203.78 0.716 0.35 1 0.35 0.35 0.251 11552.18 0.265 0.20 1 0.20 0.20 0.053 1 0.00 0.00 0 454385.97 10.43 3.611 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =3.36 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 30.79 2 5.84 19.62 3 4.49 15.07 4 3.72 12.50 5 3.22 10.82 10 2.05 6.89 15 1.58 5.30 20 1.31 4.39 25 1.13 3.80 30 1.00 3.37 35 0.91 3.05 40 0.83 2.80 45 0.77 2.59 50 0.72 2.42 55 0.68 2.28 60 0.64 2.15 75 0.55 1.86 90 0.49 1.65 105 0.44 1.49 120 0.41 1.37 150 0.35 1.19 180 0.31 1.05 3,146.04 ft3 5.30 (ft3/s) Existing Residential RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN C - POST-DEVELOPMENT CONDITIONS Surface Type = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume Open Space Totals = = 0.3222 Cwd x Cf =0.32 Runoff Volume Discharge Volume Site Detention (ft3) (ft 3) (ft 3) 1847.25 108.00 1739.25 2354.43 216.00 2138.43 2713.43 324.00 2389.43 3000.87 432.00 2568.87 3244.63 540.00 2704.63 4135.48 1080.00 3055.48 4766.04 1620.00 3146.04 5270.92 2160.00 3110.92 5699.09 2700.00 2999.09 6074.61 3240.00 2834.61 6411.36 3780.00 2631.36 6718.11 4320.00 2398.11 7000.85 4860.00 2140.85 7263.83 5400.00 1863.83 7510.23 5940.00 1570.23 7742.46 6480.00 1262.46 8371.39 8100.00 271.39 New Residential 11372.91 19440.00 ----- 9868.24 12960.00 ----- 10669.85 16200.00 ----- 8923.00 9720.00 ----- 9417.65 11340.00 ----- = Project: Meadow Bridge Subdivision Project #: BOZ_05021.28 Date: 01/06/2025 Design Storm Frequency =10 years Discharge Rate, d =0.20 cfs Input values for runoff coefficients from appropriate tables. Area Area Runoff Coefficient Frequency Factor Calculation Value A A/(43560 ft2/acre)C Cf C x Cf C' C' x A (ft2)(Acres)=(C x Cf) < or = 1 (Acres) 17591.45 0.404 0.60 1 0.60 0.60 0.24 30611.80 0.703 0.60 1 0.60 0.60 0.42 15979.09 0.367 0.35 1 0.35 0.35 0.13 8654.0439 0.199 0.20 1 0.20 0.20 0.04 1 0.00 0.00 0 1 0.00 0.00 0 72836.3718 1.6721 0.8321 Weighted Runoff Coefficient, Cwd SCjAj SAj Cwd x Cf x SAj =0.41 Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Rainfall Rainfall Peak Flow Duration, t Intensity, i = Cwd x SAj x i (min) (in/hr)(ft3/s) 1 9.16 3.76 2 5.84 2.40 3 4.49 1.84 4 3.72 1.53 5 3.22 1.32 10 2.05 0.84 15 1.58 0.65 20 1.31 0.54 25 1.13 0.46 30 1.00 0.41 35 0.91 0.37 40 0.83 0.34 45 0.77 0.32 50 0.72 0.30 55 0.68 0.28 60 0.64 0.26 75 0.55 0.23 90 0.49 0.20 105 0.44 0.18 120 0.41 0.17 150 0.35 0.14 180 0.31 0.13 403.77 ft3 0.54 (ft3/s) Existing Right-of-way RATIONAL METHOD FOR RUNOFF CALCULATIONS BASIN D - POST-DEVELOPMENT CONDITIONS Surface Type Residential New Open Space Totals = 0.2455 Cwd x Cf =0.25 Runoff Volume Discharge Volume Site Detention = = Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume (ft3) (ft 3) (ft 3) 225.62 12.00 213.62 287.56 24.00 263.56 331.41 36.00 295.41 366.51 48.00 318.51 396.29 60.00 336.29 505.09 120.00 385.09 582.10 180.00 402.10 643.77 240.00 403.77 696.06 300.00 396.06 741.93 360.00 381.93 783.06 420.00 363.06 820.52 480.00 340.52 855.05 540.00 315.05 887.17 600.00 287.17 1089.82 1080.00 9.82 917.27 660.00 257.27 945.63 720.00 225.63 New Right-of-way 1303.17 1800.00 ----- 1389.04 2160.00 ----- 1150.23 1260.00 ----- 1205.27 1440.00 ----- 1022.45 900.00 122.45 = Subbasin A Outlet Orifice/Weir Calculation Orifice (Unknown Q) 1.5 ft User Enter Desired Value 0.6 0.1149 ft2 32.2 ft/s2 0.7 cfs Weir (Unknown Q): 1.5 ft 3.367 Length (L):0.0766 ft Flow (Q) = Cw ∙ L ∙ h ^ (1.5) Flow (Q) =0.5 cfs Discharge Coeff. (Cw): Flow (Q) = C ∙ A ∙ (2 ∙ g ∙ h) ^ (0.5) Head Water Depth (h): Head Water Depth (h): Discharge Coeff. (Cd): Open Area (A): Gravity (g): Flow (Q) = Subbasin B Outlet Orifice/Weir Calculation Orifice (Unknown Q) 1.5 ft User Enter Desired Value 0.6 0.2617 ft2 32.2 ft/s2 1.5 cfs Weir (Unknown Q): 1.5 ft 3.367 Length (L):0.174469 ft Flow (Q) = Cw ∙ L ∙ h ^ (1.5) Flow (Q) =1.1 cfs Head Water Depth (h): Discharge Coeff. (Cw): Head Water Depth (h): Discharge Coeff. (Cd): Open Area (A): Gravity (g): Flow (Q) = C ∙ A ∙ (2 ∙ g ∙ h) ^ (0.5) Flow (Q) = Subbasin C Outlet Orifice/Weir Calculation Orifice (Unknown Q) 1.5 ft User Enter Desired Value 0.6 0.4345 ft2 32.2 ft/s2 2.6 cfs Weir (Unknown Q): 1.5 ft 3.367 Length (L):0.289699 ft Flow (Q) = Cw ∙ L ∙ h ^ (1.5) Flow (Q) =1.8 cfs Head Water Depth (h): Discharge Coeff. (Cw): Head Water Depth (h): Discharge Coeff. (Cd): Open Area (A): Gravity (g): Flow (Q) = C ∙ A ∙ (2 ∙ g ∙ h) ^ (0.5) Flow (Q) = Subbasin D Outlet Orifice/Weir Calculation Orifice (Unknown Q) 1.5 ft User Enter Desired Value 0.6 0.0507 ft2 32.2 ft/s2 0.3 cfs Weir (Unknown Q): 1.5 ft 3.367 Length (L):0.03382 ft Flow (Q) = Cw ∙ L ∙ h ^ (1.5) Flow (Q) =0.2 cfs Head Water Depth (h): Discharge Coeff. (Cw): Head Water Depth (h): Discharge Coeff. (Cd): Open Area (A): Gravity (g): Flow (Q) = C ∙ A ∙ (2 ∙ g ∙ h) ^ (0.5) Flow (Q) = MEADOW BRDIGE SUBDIVISION Project # BOZ_05021.28 APPENDIX D O&M PLAN April 2025 Project No. Boz_05021.28 STORM DRAINAGE FACILITY MAINTENANCE PLAN FOR MEADOW BRIDGE SUBDIVISION BOZEMAN, MONTANA OVERVIEW NARRATIVE The purpose of this maintenance plan is to outline the necessary details related to ownership, responsibility, and cleaning schedule for the storm drainage facilities for Meadow Bridge Subdivision. This plan has been completed in accordance with The City of Bozeman Design Standards and Specifications Policy, dated October 2024. The site stormwater improvements have been designed with the intent to meet the current City of Bozeman drainage regulations for the entire site to the extent feasible. Specific site information and criteria are described below: I. Ownership of Facilities Meadow Bridge, LLC Until a homeowner’s association (HOA) for the Meadow Bridge Subdivision is established, Meadow Bridge, LLC will own the proposed surface ponds. Once an HOA for the subdivision has been established, the HOA will be the responsible party for the stormwater pond maintenance. II. Inspection Thresholds for Cleaning Dry Surface Pond If sediment reduces pond volume by 25%, clean pond banks and bottom manually or mechanically. Wet Surface Pond If sediment reduces pond volume by 25%, clean pond banks and bottom manually or mechanically. III. Cleaning Dry Surface Pond To clean the pond manually or mechanically and remove sediment and debris from the pond banks and bottom. Wet Surface Pond To clean the pond mechanically and remove sediment and debris from the pond bottom to maintain volume and deter algae growth. Harvesting of vegetation may also be desirable for nutrient removal. When removing vegetation from the pond, take care not to create or leave areas of disturbed soil susceptible to erosion. If removal of vegetation results in disturbed soils, implement proper erosion and sediment control BMPs until vegetative cover is reestablished. Outlet Structure To clean grate of structure, remove and dispose of debris clogging the grate. To clean the structure, use catch basin vacuum to remove sediment and debris including discharge piping. IV. Inspection, Maintenance, and Replacement Schedule Dry Surface Pond Inspection: Every six (6) months and after storm events larger than 0.5 inches of precipitation Maintenance: Remove sediment accumulation from the pond bottom, remove trash, undesirable vegetation, and noxious weeds. Repair pond area such as sidewalls due to erosion, settlement, or rodent damage. Design Life/Replacement Schedule: 100 years Wet Surface Pond Inspection: Every six (6) months and after storm events larger than 0.5 inches of precipitation Maintenance: Remove sediment accumulation from the pond bottom, remove trash, undesirable vegetation, mosquito larvae, and noxious weeds. Repair pond area such as sidewalls due to erosion, settlement, or rodent damage. Design Life/Replacement Schedule: 100 years Outlet Structure Inspection: Every 6 months and after storm events larger than 0.5 inches of precipitation Maintenance: Clean grate of structure and vacuum sediment and debris out of the sump every 5 years or as needed based on inspection. Ensure discharge pipe is free of debris and sediment. Design Life/Replacement Schedule: 50 years V. Responsible Party Meadow Bridge, LLC Until a homeowner’s association (HOA) for the Meadow Bridge Subdivision is established, Meadow Bridge, LLC will be responsible for the inspection, maintenance, and replacement of all stormwater ponds located within the project limits. Once an HOA for the subdivision has been established, the HOA will be the responsible party for the stormwater pond maintenance. I agree to the above inspection, maintenance, and replacement schedule detailed above. Signature: ____________________________________ Meadow Bridge, LLC Representative EXHIBIT A 100 50 0 SCALE:1" = 100' 100 200 MEADOW BRIDGE SUBDIVISION Project # BOZ_05021.28 APPENDIX E GEOTECHNICAL REPORT MEADOW BRIDGE SUBDIVISION Project # BOZ_05021.28 APPENDIX F GROUNDWATER MONITORING MW-1 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 6/3/2024, 4996.101 4985.000 4990.000 4995.000 5000.000 5005.000 5010.000 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-1 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) GW Depth Below Ground Surface (ft) GW Elevation (ft) 1/31/2024 AB 5001.200 5003.051 1.851 - - - 2/7/2024 AB 5001.200 5003.051 1.851 - - - 2/14/2024 AB 5001.200 5003.051 1.851 - - - 2/21/2024 AB 5001.200 5003.051 1.851 - - - 4/4/2024 AB 5001.200 5003.051 1.851 - - - 5/1/2024 AB 5001.200 5003.051 1.851 9.9 8.049 4993.151 5/15/2024 RP 5001.200 5003.051 1.851 7.01 5.159 4996.041 6/3/2024 EH 5001.200 5003.051 1.851 6.95 5.099 4996.101 7/1/2024 RP 5001.200 5003.051 1.851 7.71 5.859 4995.341 8/1/2024 EH 5001.200 5003.051 1.851 8.23 6.379 4994.821 9/4/2024 AB 5001.200 5003.051 1.851 8.48 6.629 4994.571 MW-1 MW-2 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 6/3/2024, 4995.347 4980 4985 4990 4995 5000 5005 5010 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-2 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) GW Depth Below Ground GW Elevation (ft) 1/31/2024 AB 4995.718 4997.107 1.389 N/A #VALUE! 2/7/2024 AB 4995.718 4997.107 1.389 7.11 5.721 4989.997 2/14/2024 AB 4995.718 4997.107 1.389 7.08 5.691 4990.027 2/21/2024 AB 4995.718 4997.107 1.389 7.23 5.841 4989.877 4/4/2024 AB 4995.718 4997.107 1.389 5.02 3.631 4992.087 5/1/2024 AB 4995.718 4997.107 1.389 3.84 2.451 4993.267 5/15/2024 RP 4995.718 4997.107 1.389 1.98 0.591 4995.127 6/3/2024 EH 4995.718 4997.107 1.389 1.76 0.371 4995.347 7/1/2024 RP 4995.718 4997.107 1.389 3.63 2.241 4993.477 8/1/2024 EH 4995.718 4997.107 1.389 5.42 4.031 4991.687 9/4/2024 AB 4995.718 4997.107 1.389 6.09 4.701 4991.017 MW-2 MW-3 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 5/15/2024, 5001.88 4985 4990 4995 5000 5005 5010 5015 5020 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-3 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) Below Ground Surface (ft) GW Elevation (ft) 1/31/2024 AB 5007.59 5008.86 1.27 8.23 6.96 5000.63 2/7/2024 AB 5007.59 5008.86 1.27 8.12 6.85 5000.74 2/14/2024 AB 5007.59 5008.86 1.27 8.16 6.89 5000.7 2/21/2024 AB 5007.59 5008.86 1.27 8.24 6.97 5000.62 4/4/2024 AB 5007.59 5008.86 1.27 7.65 6.38 5001.21 5/1/2024 AB 5007.59 5008.86 1.27 7.96 6.69 5000.9 5/15/2024 RP 5007.59 5008.86 1.27 6.98 5.71 5001.88 6/3/2024 EH 5007.59 5008.86 1.27 7.51 6.24 5001.35 7/1/2024 RP 5007.59 5008.86 1.27 8.09 6.82 5000.77 8/1/2024 EH 5007.59 5008.86 1.27 8.54 7.27 5000.32 9/4/2024 AB 5007.59 5008.86 1.27 8.21 6.94 5000.65 MW-3 MW-4 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 5/15/2024, 5011.52 5000 5005 5010 5015 5020 5025 5030 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-4 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) GW Depth Below Ground Surface (ft) GW Elevation (ft) 1/31/2024 AB 5017.88 5019.7 1.82 9.17 7.35 5010.53 2/7/2024 AB 5017.88 5019.7 1.82 9 7.18 5010.7 2/14/2024 AB 5017.88 5019.7 1.82 9.12 7.3 5010.58 2/21/2024 AB 5017.88 5019.7 1.82 9.3 7.48 5010.4 4/4/2024 AB 5017.88 5019.7 1.82 8.72 6.9 5010.98 5/1/2024 AB 5017.88 5019.7 1.82 9.14 7.32 5010.56 5/15/2024 RP 5017.88 5019.7 1.82 8.18 6.36 5011.52 6/3/2024 EH 5017.88 5019.7 1.82 8.62 6.8 5011.08 7/1/2024 RP 5017.88 5019.7 1.82 9.28 7.46 5010.42 8/1/2024 EH 5017.88 5019.7 1.82 9.56 7.74 5010.14 9/4/2024 AB 5017.88 5019.7 1.82 9.3 7.48 5010.4 MW-4 MW-5 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 5/15/2024, 5011.45 5000 5005 5010 5015 5020 5025 5030 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-5 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) GW Depth Below Ground Surface (ft) GW Elevation (ft) 1/31/2024 AB 5016.98 5018.44 1.46 7.96 6.5 5010.48 2/7/2024 AB 5016.98 5018.44 1.46 7.82 6.36 5010.62 2/14/2024 AB 5016.98 5018.44 1.46 7.93 6.47 5010.51 2/21/2024 AB 5016.98 5018.44 1.46 8.15 6.69 5010.29 4/4/2024 AB 5016.98 5018.44 1.46 7.58 6.12 5010.86 5/1/2024 AB 5016.98 5018.44 1.46 7.9 6.44 5010.54 5/15/2024 RP 5016.98 5018.44 1.46 6.99 5.53 5011.45 6/3/2024 EH 5016.98 5018.44 1.46 7.38 5.92 5011.06 7/1/2024 RP 5016.98 5018.44 1.46 8.01 6.55 5010.43 8/1/2024 EH 5016.98 5018.44 1.46 8.33 6.87 5010.11 9/4/2024 AB 5016.98 5018.44 1.46 8.02 6.56 5010.42 MW-5 MW-6 *Highlighted row designates peak groundwater elevation. Peak elevation also shown on graph above. BOZO5021.28 Meadow Bridge GW Summary by Manual Measurement As of September 4th, 2024 5/15/2024, 4989.58 4980 4985 4990 4995 5000 5005 5010 1/31/2024 3/21/2024 5/10/2024 6/29/2024 8/18/2024 10/7/2024 MW-6 Groundwater Monitoring Ground Surface Elevation (ft)Top of Casing Elevation (ft)GW Elevation (ft) Date Monitored By (Initials) Ground Surface Elevation (ft) Top of Casing Elevation (ft) Casing Height (ft) TOC to GW Depth (ft) GW Depth Below Ground Surface (ft) GW Elevation (ft) 1/31/2024 AB 4992.79 4994.72 1.93 6.35 4.42 4988.37 2/7/2024 AB 4992.79 4994.72 1.93 5.95 4.02 4988.77 2/14/2024 AB 4992.79 4994.72 1.93 5.94 4.01 4988.78 2/21/2024 AB 4992.79 4994.72 1.93 6.06 4.13 4988.66 4/4/2024 AB 4992.79 4994.72 1.93 5.39 3.46 4989.33 5/1/2024 AB 4992.79 4994.72 1.93 5.45 3.52 4989.27 5/15/2024 RP 4992.79 4994.72 1.93 5.14 3.21 4989.58 6/3/2024 EH 4992.79 4994.72 1.93 5.22 3.29 4989.5 7/1/2024 RP 4992.79 4994.72 1.93 5.55 3.62 4989.17 8/1/2024 EH 4992.79 4994.72 1.93 6.68 4.75 4988.04 9/4/2024 AB 4992.79 4994.72 1.93 6.09 4.16 4988.63 MW-6