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HomeMy WebLinkAboutNelson Meadows Lot 15_Stormwater Report Stormwater Report: for NELSON MEADOWS LOT 15 Gallatin County, Montana September, 2025 Prepared For: Delesalle Projects Montana INC Prepared By: Hyalite Engineers, PLLC Brett Megaard, PE Page 1 NELSON MEADOWS LOT 15 ENGINEER’S STORM DRAINAGE DESIGN REPORT Owner: Delesalle Projects Montana INC 400-1788 W 5th Ave Vancouver, V6J1P2 BC Introduction This report provides a design basis and hydrologic calculations for sizing stormwater infrastructure for Nelson Meadows Lot 15. The project site is located 0.12 miles west of the Royal Wolf Way and Nelson Road intersection. This project in total is 2.67 acres of commercial and residential development constructed in one proposed phase. The owner would like to construct three buildings. The existing site has topography sloping at approximately -2% to the west. There is currently no existing stormwater infrastructure on the lot. All precipitation is currently either contained on site through absorption and infiltration or runs offsite to Cattail Creek on the west side of the property. The City of Bozeman Design Standards and Specifications (October 2024) was used as the primary guideline for this stormwater drainage design. General Design The proposed development of the site will be 72% impervious area containing buildings, asphalt driveways, and concrete walkways and 28% pervious area of undisturbed land. Groundwater observed on the site was found at a seasonal high of 5.5’. The proposed building will have roof drains that will capture rainwater which will then be routed to a surface detention pond. Hydrologic Methodology The rational method was used to determine peak runoff rates. The rational formula provides a peak runoff rate which occurs at the time of concentration. Q = CIA V = DQ Where: C = Weighted C Factor I = Storm Intensity (in/hr) A = Area (acres) Q = Runoff (cfs) D= Duration (s) V = Volume (cf) Detention volumes were analyzed for the 10-year 2-hour and 100-year 2-hour and 24-hour storms using Figure I-3 from The City of Bozeman design Standards (October 2024). Runoff coefficients and watershed flow calculations are included in Appendix A. Page 2 Stormwater Detention Pond The stormwater detention pond was designed to be sized for the development of Nelson Meadows Lot 15. The proposed 327’x14’ detention pond will be installed to account for the runoff from Basin 1. There is only one stormwater basin for site. Basin 1 will run to the detention pond from direct runoff or will be routed to the pond. A drainage area exhibit is included with this report in Appendix B. The stormwater calculations for these areas are included in Appendix A. Flooding Excessive runoff from a large storm event will be routed such that runoff does not inundate home sites, drainfields or over top the roadway. Finished floor elevations of buildings will be set higher than the surrounding ground with finished ground sloping away from them. In the event that the pond overtops, stormwater will spill to the west away from the proposed buildings. Appendix A – Stormwater Detention Pond Calculations Appendix B – Drainage Area Exhibit N E L S O N M E A D O W S L O T 1 5 J U N E 2 0 2 5 A P P E N D I X APPENDIX A STORMWATER DETENTION POND CALCULATIONS 2 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 2.08 3.97 1190 119.5 1070Time To Concentration TcTime To Concentration Tc10 0.17 1.53 2.92 1751 239.1 1511Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 1.24 2.36 2128 358.6 1769Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 0.99 1.89 2265 478.1 178725 0.42 0.84 1.60 2403 597.7 1805P2 = 10-yr 24 hour rainfall depth in 1.18Per COB P2 = 10-yr 24 hour rainfall depth in 1.18 30 0.50 0.75 1.43 2574 717.2 1857n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 0.66 1.26 2643 836.7 1806L = Length 150.00ftL = Length 150.00ft40 0.67 0.59 1.13 2700 956.3 1744S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 0.54 1.03 2780 1075.8 170450 0.83 0.49 0.93 2803 1195.3 1608Tc = 24.04MinutesTc = 4.81Minutes55 0.92 0.45 0.86 2832 1314.9 151760 1.00 0.42 0.80 2883 1434.4 1449Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.24 0.46 3295 2868.8 426V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.19 0.36 3913 4303.3 -390360 6.00 0.12 0.23 4943 8606.5 -3664Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.08 0.15 6590 17213 -10623k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes3200ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 30.56 Minutes Tc = 6.26 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 0.75in/hri = 2.08in/hrQ = CiAQ = 0.40cfsQ = CiAQ = 3.97cfsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Rv = 0.05 + 0.9(I)I = Percent imperviousOpen Land Open LandTotals TotalsCW = CW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsLot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*Area 5 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 3.16 6.03 1808 191.3 1616Time To Concentration TcTime To Concentration Tc10 0.17 2.31 4.40 2643 382.5 2260Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 1.87 3.57 3209 573.8 2635Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 1.50 2.86 3432 765.0 266725 0.42 1.28 2.44 3661 956.3 2705P2 = 10-yr 24 hour rainfall depth in 1.49Per COB P2 = 10-yr 24 hour rainfall depth in 1.49 30 0.50 1.13 2.15 3879 1147.5 2731n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 0.99 1.89 3964 1338.8 2626L = Length 150.00ftL = Length 150.00ft40 0.67 0.89 1.70 4073 1530.0 2543S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 0.81 1.54 4170 1721.3 244950 0.83 0.74 1.41 4233 1912.6 2321Tc = 21.40MinutesTc = 4.28Minutes55 0.92 0.69 1.32 4342 2103.8 223860 1.00 0.64 1.22 4393 2295.1 2098Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.34 0.65 4668 4590.1 78V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.25 0.48 5149 6885.2 -1737360 6.00 0.15 0.29 6178 13770.4 -7592Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.09 0.17 7414 27541 -20127k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes3200ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 27.91 Minutes Tc = 5.73 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 1.20in/hri = 3.16in/hrQ = CiAQ = 0.64cfsQ = CiAQ = 6.03cfsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Rv = 0.05 + 0.9(I)I = Percent imperviousOpen Land Open LandTotals TotalsCW = CW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsLot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*Area 10 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 3.87 7.38 2214 242.3 1972Time To Concentration TcTime To Concentration Tc10 0.17 2.83 5.40 3238 484.5 2753Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 2.29 4.37 3930 726.8 3203Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 1.84 3.51 4210 969.0 324125 0.42 1.56 2.97 4462 1211.3 3251P2 = 10-yr 24 hour rainfall depth in 1.70Per COB P2 = 10-yr 24 hour rainfall depth in 1.70 30 0.50 1.38 2.63 4737 1453.5 3283n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 1.22 2.33 4885 1695.8 3190L = Length 150.00ftL = Length 150.00ft40 0.67 1.09 2.08 4988 1938.1 3050S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 1.00 1.91 5149 2180.3 296850 0.83 0.91 1.74 5206 2422.6 2783Tc = 20.03MinutesTc = 4.00Minutes55 0.92 0.84 1.60 5286 2664.8 262160 1.00 0.79 1.51 5423 2907.1 2516Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.41 0.78 5629 5814.2 -185V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.29 0.55 5972 8721.3 -2749360 6.00 0.17 0.32 7002 17442.5 -10440Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.10 0.19 8238 34885 -26647k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes3283ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 26.55 Minutes Tc = 5.45 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 1.52in/hri = 3.87in/hrQ = CiAQ = 0.81cfsQ = CiAQ = 7.38cfsI = Percent imperviousRv = 0.05 + 0.9(I)Lot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*AreaCW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Open Land Open LandTotals TotalsCW = 25 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 4.76 9.08 2723 307.6 2415Time To Concentration TcTime To Concentration Tc10 0.17 3.48 6.64 3982 615.2 3366Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 2.83 5.40 4857 922.8 3934Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 2.26 4.31 5171 1230.4 394125 0.42 1.93 3.68 5520 1538.0 3982P2 = 10-yr 24 hour rainfall depth in 1.96Per COB P2 = 10-yr 24 hour rainfall depth in 1.96 30 0.50 1.70 3.24 5835 1845.6 3989n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 1.50 2.86 6007 2153.2 3853L = Length 150.00ftL = Length 150.00ft40 0.67 1.35 2.57 6178 2460.8 3717S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 1.23 2.35 6333 2768.4 356450 0.83 1.12 2.14 6407 3076.0 3331Tc = 18.66MinutesTc = 3.73Minutes55 0.92 1.04 1.98 6544 3383.6 316160 1.00 0.97 1.85 6659 3691.2 2968Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.49 0.93 6727 7382.5 -655V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.34 0.65 7002 11073.7 -4072360 6.00 0.19 0.36 7826 22147.4 -14322Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.12 0.23 9885 44295 -34410k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes3989ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 25.17 Minutes Tc = 5.18 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 1.93in/hri = 4.76in/hrQ = CiAQ = 1.03cfsQ = CiAQ = 9.08cfsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Rv = 0.05 + 0.9(I)I = Percent imperviousOpen Land Open LandTotals TotalsCW = CW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsLot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*Area 50 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 5.43 10.35 3106 358.6 2748Time To Concentration TcTime To Concentration Tc10 0.17 3.97 7.57 4542 717.2 3825Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 3.22 6.14 5526 1075.8 4450Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 2.58 4.92 5904 1434.4 446925 0.42 2.20 4.20 6293 1793.0 4500P2 = 10-yr 24 hour rainfall depth in 2.15Per COB P2 = 10-yr 24 hour rainfall depth in 2.15 30 0.50 1.94 3.70 6659 2151.6 4507n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 1.71 3.26 6848 2510.2 4337L = Length 150.00ftL = Length 150.00ft40 0.67 1.53 2.92 7002 2868.8 4133S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 1.40 2.67 7208 3227.4 398150 0.83 1.28 2.44 7322 3586.0 3736Tc = 17.81MinutesTc = 3.56Minutes55 0.92 1.18 2.25 7425 3944.7 348160 1.00 1.10 2.10 7551 4303.3 3248Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.55 1.05 7551 8606.5 -1055V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.37 0.71 7620 12909.8 -5290360 6.00 0.21 0.40 8650 25819.5 -17170Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.13 0.25 10709 51639 -40930k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes4507ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 24.33 Minutes Tc = 5.01 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 2.25in/hri = 5.43in/hrQ = CiAQ = 1.20cfsQ = CiAQ = 10.35cfsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Rv = 0.05 + 0.9(I)I = Percent imperviousOpen Land Open LandTotals TotalsCW = CW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsLot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*Area 100 yrExisting ConditionsProposed ConditionsBasin Sizing CalculationsWeighted C Value (Pre-Dev) Weighted C Value (Post-Dev) Infiltration*Only used for 100-year analysisArea Area Area AreaObserved Percolation Rate 7.50 min/in(ft2) (acres) (ft2) (acres)8.00 in/hr0.95 0.00 0.00 0.95 45528 1.05 0.990.22 0.00 0.00 0.22 36796 0.84 0.19 Design Percolation Rate 4.00 in/hr0.95 0.00 0.00 0.95 33386 0.77 0.73 Infiltrative Area 6300ft20.20 115710 2.66 0.53 0.20 0.00 0.00 Design Infiltration Rate 0.583 cfs115710 2.66 0.53 115710 2.66 1.91Duration Duration Intensity Q Runoff Release Required0.20 0.72min hr in/hr cfs Volume Volume Storage 5 0.08 6.09 11.61 3484 424.0 3060Time To Concentration TcTime To Concentration Tc10 0.17 4.45 8.49 5091 847.9 4243Tc Overland Flow (Up to 150ft) Tc Overland Flow (Up to 150ft)15 0.25 3.61 6.88 6195 1271.9 4924Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) Tt = (0.42/P2^0.5)*(nL/S)^0.8 (HEC 22 EQ 4.3) 20 0.33 2.89 5.51 6613 1695.8 491725 0.42 2.46 4.69 7036 2119.8 4917P2 = 10-yr 24 hour rainfall depth in 2.34Per COB P2 = 10-yr 24 hour rainfall depth in 2.15 30 0.50 2.18 4.16 7483 2543.7 4939n = roughness coefficent 0.15 n = roughness coefficent 0.01 35 0.58 1.92 3.66 7689 2967.7 4721L = Length 150.00ftL = Length 150.00ft40 0.67 1.72 3.28 7872 3391.6 4480S = Slope ft/ft 0.02ft/ftS = Slope ft/ft 0.01ft/ft45 0.75 1.57 2.99 8083 3815.6 426850 0.83 1.44 2.75 8238 4239.5 3998Tc = 17.07MinutesTc = 3.56Minutes55 0.92 1.33 2.54 8369 4663.5 370660 1.00 1.24 2.36 8512 5087.4 3425Tc Shallow Concentrated Flow (After 400ft) Tc Shallow Concentrated Flow (After 400ft)120 2.00 0.61 1.16 8375 10174.8 -1800V = KukSp0.5 (HEC 22 eqn 4.4) V = KukSp0.5 (HEC 22 eqn 3-4)180 3.00 0.41 0.78 8444 15262.2 -6819360 6.00 0.22 0.42 9061 30524.4 -21463Ku = Conversion Factor3.28English UnitsKu = Conversion Factor3.28English Units720 12.00 0.14 0.27 11533 61049 -49516k = Intercept Coefiicient 0.21HEC 22 Table 4.3k = Intercept Coefiicient 0.62HEC 22 Table 4.3Runoff Treatment Volume (Initial 0.5")Sp = Slope %1.66%Sp = Slope %0.50%0.66 in0.7 decimal percentV = 0.90ft/sV = 1.44ft/s2.66 acresD = 352.00ftD = 125.00ft3200ft3Tc =6.52MinutesTc =1.45Minutes4939ft3Total Tc (Overland and Shallow Concentrated) Total Tc (Overland and Shallow Concentrated)Tc = 23.59 Minutes Tc = 5.01 MinutesRunoff Rate (Intensity @ Tc) Runoff Rate (Intensity @ Tc)Reference table 6.5.2 in COB Design Standards Reference table 6.5.2 in COB Design Standardsi = 2.66in/hri = 6.09in/hrQ = CiAQ = 1.41cfsQ = CiAQ = 11.61cfsArea = Initial 0.5" Pond Volume Req. =Minimum Pond Size Required = Rv = 0.05 + 0.9(I)I = Percent imperviousOpen Land Open LandTotals TotalsCW = CW =Asphaltic and Concrete Asphaltic and ConcreteHeavy Soil (average) Heavy Soil (average)Drives, Walks and Roofs Drives, Walks and RoofsLot 15 of Nelson Meadows Basin 1Design Storm Frequency =Land UseC C*AreaLand UseC C*Area Pond Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Tuesday, 09 / 16 / 2025 Pond No. 1 - 1 Pond Data Trapezoid -Bottom L x W = 315.4 x 2.0 ft, Side slope = 3.00:1, Bottom elev. = 4591.73 ft, Depth = 2.00 ft Stage / Storage Table Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft) 0.00 4591.73 631 0 0 0.20 4591.93 1,013 164 164 0.40 4592.13 1,398 241 405 0.60 4592.33 1,786 318 724 0.80 4592.53 2,177 396 1,120 1.00 4592.73 2,571 475 1,595 1.20 4592.93 2,967 554 2,149 1.40 4593.13 3,367 633 2,782 1.60 4593.33 3,769 714 3,496 1.80 4593.53 4,175 794 4,290 2.00 4593.73 4,583 876 5,166 Culvert / Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in)= 0.00 0.00 0.00 0.00 Span (in)= 0.00 0.00 0.00 0.00 No. Barrels = 0 0 0 0 Invert El. (ft)= 0.00 0.00 0.00 0.00 Length (ft)= 0.00 0.00 0.00 0.00 Slope (%)= 0.00 0.00 0.00 n/a N-Value = .013 .013 .013 n/a Orifice Coeff.= 0.60 0.60 0.60 0.60 Multi-Stage = n/a No No No Crest Len (ft)= 2.30 0.00 0.00 0.00 Crest El. (ft)= 4593.33 0.00 0.00 0.00 Weir Coeff.= 3.33 3.33 3.33 3.33 Weir Type = Rect --- --- --- Multi-Stage = No No No No Exfil.(in/hr)= 0.000 (by Wet area) TW Elev. (ft)= 0.00 Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s). Stage / Storage / Discharge Table Stage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Total ft cuft ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs 0.00 0 4591.73 --- --- --- --- 0.00 --- --- --- --- --- 0.000 0.20 164 4591.93 --- --- --- --- 0.00 --- --- --- --- --- 0.000 0.40 405 4592.13 --- --- --- --- 0.00 --- --- --- --- --- 0.000 0.60 724 4592.33 --- --- --- --- 0.00 --- --- --- --- --- 0.000 0.80 1,120 4592.53 --- --- --- --- 0.00 --- --- --- --- --- 0.000 1.00 1,595 4592.73 --- --- --- --- 0.00 --- --- --- --- --- 0.000 1.20 2,149 4592.93 --- --- --- --- 0.00 --- --- --- --- --- 0.000 1.40 2,782 4593.13 --- --- --- --- 0.00 --- --- --- --- --- 0.000 1.60 3,496 4593.33 --- --- --- --- 0.00 --- --- --- --- --- 0.000 1.80 4,290 4593.53 --- --- --- --- 0.68 --- --- --- --- --- 0.684 2.00 5,166 4593.73 --- --- --- --- 1.94 --- --- --- --- --- 1.937 N E L S O N M E A D O W S L O T 1 5 J U N E 2 0 2 5 A P P E N D I X APPENDIX B DRAINAGE AREA EXHIBIT MWSSSS16''W16''W16''W16''W16''W16''W16''W16''W16''W16''W6''S HYD0'30'60'90'C1.0AS NOTEDDRAINAGE AREAEXHIBITCKHEC Sep 16, 2025 - 9:33amCAD FILE: M:\213740\Drawings\Exhibits\Drainage Basins.dwg REVISIONSDATEPROJECT NUMBERHYALITE Engineers, PLLC161 W HALEY SPRINGSBozeman, MT 59718Tel: (406) 587.2781w w w . hyaliteeng. comFax: (406) 522.92252018LOT 15 NELSON MEADOWS BOZEMAN, MT6/23/202521374022x34 originals SCALESHEET TITLEDESIGN BYMONTANABRETT C.No. 29106 PEMEGAARDPEFORSOILNASREN I G ENE P R E L I M I N A R Y ROAD, STE. 101APPROXIMATEPROPERTY BOUNDARYPROPOSEDBUILDINGPRINCE LANEHEC Sep 16, 2025 - 9:33amCAD FILE: M:\213740\Drawings\Exhibits\Drainage Basins.dwg REVISIONSDATEPROJECT NUMBERHYALITE Engineers, PLLC161 W HALEY SPRINGSBozeman, MT 59718Tel: (406) 587.2781w w w . hyaliteeng. comFax: (406) 522.92252018LOT 15 NELSON MEADOWS BOZEMAN, MT6/23/202521374022x34 originals SCALESHEET TITLEDESIGN BYMONTANABRETT C.No. 29106 PEMEGAARDPEFORSOILNASREN I G ENE P R E L I M I N A R Y ROAD, STE. 101PROPOSEDBUILDINGPROPOSEDBUILDINGEXISTING SECONDARY ACCESS STORMWATER BASIN 1 - 2.66 ACRESLEGENDNelson Meadows Lot 15DRAINAGE AREAPROPOSED DETENTION POND