HomeMy WebLinkAbout021_DraingageReport NORTH PARK WESTSIDE PRELIMINARY DRAINAGE REPORT Project # 21349.03 Bozeman, Montana 59718 JUNE 25, 2025
NORTH PARK WESTSIDE PRELIMINARY DRAINAGE REPORT BOZEMAN, MONTANA CERTIFICATION I hereby state that this Preliminary Drainage Report has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community of professional engineers. The analysis has been prepared utilizing procedures and practices specified by the City of Bozeman and within the standard accepted practices. 06/25/2025 Robert P. Egeberg, P.E. Date
June 25, 2025 Project No. 21349.03 PRELIMINARY DRAINAGE REPORT NORTH PARK WESTSIDE BOZEMAN, MONTANA 59718 OVERVIEW NARRATIVE The purpose of this preliminary drainage report is to present a summary of calculations to quantify the stormwater runoff for the North Park Westside project. All design criteria and calculations were originally prepared in accordance with The City of Bozeman Design Standards and Specifications Policy, dated March 2004 but have been updated to comply with the latest design and construction standards update, dated October 2024. The site stormwater improvements have been designed with the intent to meet the current drainage regulations for the City of Bozeman. LOCATION The North Park Westside development area is bordered by Interstate 90 on the western boundary, the now abandoned Red Wing Drive to the north, North 7th Avenue on the eastern side, and Mandeville Drive to the south. The presence of Mandeville Creek serves as a general division between the properties of North Park Westside and East developments. EXISTING SITE CONDITIONS The land cover surrounding the proposed roadways of Wheat Drive and Cultivar Street is generally vacant grassland. Runoff is generally conveyed northwest across the site, with water on the east side flowing into Mandeville Creek. Runoff that is within 300-feet to the west of Mandeville Creek will also flow into Mandeville Creek. Slopes along the existing property vary from zero to seven (7) percent. The existing site has three (3) total watersheds. Existing watershed basins are shown in Exhibit A of Appendix A. Preliminary hydrologic calculations for these watersheds can be found in Appendix B.
P:21349_03_North_Park_Westside_MSP_TO_#3 (06/25/25) DME/RPE PROPOSED PROJECT The proposed improvements for North Park Westside development include roads, sidewalks, open space and detention ponds. The proposed area of the development has been broken into three (3) total basins as shown in Exhibit B in Appendix A. Preliminary hydrologic calculations for these watersheds can be found in Appendix C. Basin A includes the connection to Cultivar Street on the southeast end of the development. Basin A runoff will be collected in gutters and transported to a curb inlet. Runoff will then flow into a detention pond located on the north side of Cultivar Street. Runoff south of Cultivar Street will have overland flow until it flows into gutters on Cultivar Street. Runoff north of Cultivar Street will flow into open land where it will infiltrate into the ground or flow into Mandeville Creek as it had in pre-development conditions. Basin B includes most of the new Cultivar Street, most of the open land in the development, and the western part of Wheat Drive. The open space runoff from the areas west of Cultivar Street will have overland flow that will flow along undeveloped land, towards the proposed surface drainage swales that follow existing drainage patterns until it reaches the proposed detention pond. Runoff that flows towards Cultivar Street and Wheat Drive will have overland flow that will flow into the nearest street. Runoff will then be collected in gutters and transported to a curb inlet. Runoff will then flow through storm drainage infrastructure and into a new surface drainage swale that outfalls to the proposed detention pond located in the northwest corner of the overall development. A box culvert is proposed in this basin where Mandeville Creek intersects Cultivar Street. Basin C includes the middle section of the proposed Wheat Drive and undeveloped land to the
south of Wheat Drive and west of Mandeville Creek. Runoff will flow overland as it had in pre-development conditions until it is intersected by Wheat Drive. Runoff will then be collected in gutters and transported to curb inlets. Runoff will then flow through storm drainage infrastructure and into a detention pond located to the north of Wheat Drive. A box culvert is proposed in this basin where Mandeville Creek intersects Wheat Drive. INLETS Inlet locations will be designed to capture runoff from the right-of-way area and limit the spread width to the crown of the street for the minor storm runoff and not to exceed 18 inches of depth at the gutter flowline during the major storm, per The City of Bozeman Design and Construction Standards. Bentley’s FlowMaster program, which uses methodology of the FHWA HEC-22 Manual, will be utilized to calculate inlet spacing. This program will be used to calculate the spread width and gutter flow depth at each of the inlets using the calculated peak post-development flow rate from the minor and major storm event. Inlets will be analyzed with a 50 percent clogging factor for sag inlets and 25 percent clogging factor for on-grade inlets. All inlets and manholes will have a nine (9) inch sump for sediment collection.
P:21349_03_North_Park_Westside_MSP_TO_#3 (06/25/25) DME/RPE PIPES The Manning’s equation will be used to analyze and design the storm drain pipes throughout the project. Unless higher strength concrete storm drain pipe is utilized, pipe slopes will be set to maintain a minimum depth of cover of two (2) feet below final grade and a minimum velocity of 2.5 fps during the minor storm. The storm drain pipes will be designed to convey the major storm event without surcharging beyond the crown of the road. When the depth of flow in the pipe exceeds full flow capacity, the next larger size pipe will be used. BASIN STORAGE FACILITY As mentioned above, three new detention ponds are proposed for the project. All detention ponds will be sized based on a ten (10) year, two (2) hour storm intensity at elevations that maintain a minimum of two feet of separation between the bottom of the proposed pond and the peak groundwater elevations. Each detention pond will have a maximum side slope of 4:1 and will have a maximum water surface depth of two and a half (2.5) feet. The surface drainage swale that will flow towards the Basin B detention pond will be sized to capture and convey the 100-year storm event with at least 1-foot of freeboard to the adjacent grade. See Appendix C for Preliminary Post-Development Hydrology Calculations. MAJOR STORM EVENTS In the event of a 100-year storm event, the proposed detention basins will overtop and be conveyed directly into Mandeville Creek or towards the swale on the northwest corner of the property in the flow direction as it has historically. Runoff within Cultivar Street and Wheat Drive will be contained and have a channelized flow within the roadways. WATER QUALITY The City of Bozeman Design and Construction Standards states the requirement to capture or reuse the runoff generated from the first half (0.5) inches of rainfall from a 24-hour storm. We will meet this requirement by detaining all runoff onsite in the proposed detention ponds. CONCLUSION The preliminary drainage plan for the North Park Westside project adheres to The City of Bozeman Design and Construction Standards, dated October 2024. Through comprehensive calculations and adherence to city regulations, the proposed stormwater system will effectively handle runoff within the area of development. Inlets, pipes, detention ponds, drainage swales 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.
P:21349_03_North_Park_Westside_MSP_TO_#3 (06/25/25) DME/RPE APPENDICES Appendix A – Watershed Exhibits Appendix B – Preliminary Pre-Development Hydrology Calculations Appendix C – Preliminary Post-Development Hydrology Calculations Appendix D – Operations and Maintenance Plan
APPENDIX A Watershed Exhibits NORTH PARK WESTSIDE
21349.03
APPENDIX B Preliminary Pre-Development Hydrology Calculations NORTH PARK WESTSIDE
21349.03
Project: North Park West
Project #: 21349.03
Date: 03/06/2024
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)00.000 0.95 1 0.95 0.95 0.000
2342359 53.773 0.15 1 0.15 0.15 8.0661
0.00 0.00 0
2342359 53.773 8.066
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =8.07
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 73.90
5 3.22 25.96
10 2.05 16.54
15 1.58 12.71
20 1.31 10.54
25 1.13 9.12
30 1.00 8.10
35 0.91 7.33
40 0.83 6.72
45 0.77 6.22
50 0.72 5.81
55 0.68 5.46
60 0.64 5.16
75 0.55 4.47
90 0.49 3.97
105 0.44 3.59
120 0.41 3.29
150 0.35 2.85
180 0.31 2.53
360 0.20 1.61
720 0.13 1.03
1440 0.08 0.65
23,686.44 ft3 16.54 (ft3 /s)
56521.45 0.00 56521.45
34793.04 0.00 34793.04
44345.83 0.00 44345.83
25610.52 0.00 25610.52
27298.06 0.00 27298.06
22604.91 0.00 22604.91
23686.44 0.00 23686.44
20093.61 0.00 20093.61
21417.63 0.00 21417.63
18026.58 0.00 18026.58
18584.01 0.00 18584.01
16803.93 0.00 16803.93
17435.16 0.00 17435.16
15388.99 0.00 15388.99
16125.29 0.00 16125.29
13679.35 0.00 13679.35
14580.72 0.00 14580.72
11439.80 0.00 11439.80
12651.64 0.00 12651.64
7788.00 0.00 7788.00
9926.28 0.00 9926.28
(ft3 ) (ft3 ) (ft3)4433.91 0.00 4433.91C wd x Cf =0.15
Runoff Volume Discharge Volume Site Detention
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1500
RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN A - PRE-DEVELOPMENT CONDITIONS
Surface Type
Impervious
Project: North Park West
Project #: 21349.03
Date: 03/06/2024
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)00.000 0.95 1 0.95 0.95 0.000
1556678 35.736 0.15 1 0.15 0.15 5.3601
0.00 0.00 0
1556678 35.736 5.360
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =5.36
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 49.11
5 3.22 17.25
10 2.05 10.99
15 1.58 8.45
20 1.31 7.01
25 1.13 6.06
30 1.00 5.38
35 0.91 4.87
40 0.83 4.47
45 0.77 4.14
50 0.72 3.86
55 0.68 3.63
60 0.64 3.43
75 0.55 2.97
90 0.49 2.64
105 0.44 2.38
120 0.41 2.19
150 0.35 1.89
180 0.31 1.68
360 0.20 1.07
720 0.13 0.68
1440 0.08 0.43
15,741.47 ft3 10.99 (ft3 /s)
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN B - PRE-DEVELOPMENT CONDITIONS
Surface Type
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1500C wd x Cf =0.15
Runoff Volume Discharge Volume Site Detention
(ft3 ) (ft3 ) (ft3)2946.67 0.00 2946.67
5175.73 0.00 5175.73
6596.78 0.00 6596.78
7602.63 0.00 7602.63
8407.99 0.00 8407.99
9090.98 0.00 9090.98
9690.01 0.00 9690.01
10227.17 0.00 10227.17
10716.50 0.00 10716.50
11167.51 0.00 11167.51
11587.01 0.00 11587.01
11980.05 0.00 11980.05
12350.51 0.00 12350.51
13353.75 0.00 13353.75
14233.66 0.00 14233.66
15022.70 0.00 15022.70
15741.47 0.00 15741.47
17020.16 0.00 17020.16
18141.67 0.00 18141.67
37562.86 0.00 37562.86
23122.65 0.00 23122.65
29471.23 0.00 29471.23
Project: North Park West
Project #: 21349.03
Date: 03/06/2024
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)
45321 1.040 0.95 1 0.95 0.95 0.988
4164075 95.594 0.15 1 0.15 0.15 14.3391
0.00 0.00 0
4209396 96.634 15.328
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =15.33
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 140.43
5 3.22 49.33
10 2.05 31.44
15 1.58 24.15
20 1.31 20.03
25 1.13 17.33
30 1.00 15.39
35 0.91 13.93
40 0.83 12.77
45 0.77 11.83
50 0.72 11.04
55 0.68 10.38
60 0.64 9.81
75 0.55 8.49
90 0.49 7.54
105 0.44 6.82
120 0.41 6.25
150 0.35 5.41
180 0.31 4.80
360 0.20 3.06
720 0.13 1.95
1440 0.08 1.24
45,010.57 ft3 31.44 (ft3 /s)
107405.84 0.00 107405.84
66116.05 0.00 66116.05
84268.92 0.00 84268.92
48666.82 0.00 48666.82
51873.60 0.00 51873.60
42955.35 0.00 42955.35
45010.57 0.00 45010.57
38183.21 0.00 38183.21
40699.20 0.00 40699.20
34255.32 0.00 34255.32
35314.57 0.00 35314.57
31931.95 0.00 31931.95
33131.46 0.00 33131.46
29243.20 0.00 29243.20
30642.35 0.00 30642.35
25994.41 0.00 25994.41
27707.25 0.00 27707.25
21738.67 0.00 21738.67
24041.50 0.00 24041.50
14799.28 0.00 14799.28
18862.58 0.00 18862.58
(ft3 ) (ft3 ) (ft3)8425.60 0.00 8425.60C wd x Cf =0.16
Runoff Volume Discharge Volume Site Detention
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1586
RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN C - PRE-DEVELOPMENT CONDITIONS
Surface Type
Impervious
North Park West
Project No: 21349.03
Date: 06/25/2025
Designer: ALS
Design Storm The minimum tc used in the City of Bozeman is 0.083 hour (5.0 minutes)
(inches)therefore for values that fall under the minimum requirment
1.18 will use a tc of 5.0 minutes. Equations Used:
1.70 20.3282
1.96 16.1345
2.15
2.34
Sheet Flow 300 0.020 0.130 --34.7
shallow - unpaved 413 0.020 --2.28 3.0
Pipe0 ----3.00 0.0
Total:37.7
Sheet Flow 300 0.030 0.150 -- 33.0
Gutter 130 0.007 -- 1.72 1.3
Pipe 72 0.005 -- 3.00 0.4
Total:34.7
Sheet Flow 300 0.015 0.130 --38.9
shallow - unpaved 3100 0.012 --1.77 29.2
Pipe0 ----3.00 0.0
Total:68.1
Sheet Flow 300 0.083 0.150 --22.0
Gutter 60 0.016 --2.56 0.4
Pipe 3359 0.075 --3.00 18.7
Total:41.1
Sheet Flow 300 0.013 0.130 --41.4
shallow - unpaved 463 0.013 --1.83 4.2
Pipe ----3.00 0.0
Total:45.7
Sheet Flow 300 0.013 0.150 --46.2
shallow - unpaved 331 0.013 --1.84 3.0
Gutter 73 0.014 --2.41 0.5
Pipe 169 0.050 --3.00 0.9
Total:50.6
*All other time of concentrations assumed to be 5minutes
25-Year, 24-Hour Unpaved Velocity Constant=
PROPOSED DETETION BASIN TIME OF CONCENTRATION WORKSHEET
Direct Runoff
2-Year, 24-Hour
10-Year, 24-Hour Paved Velocity Constant=
50-Year, 24-Hour
100-Year, 24-Hour
Outall Location/
Major Flow Type Flow
Length (ft)
Flow Slope
(ft/ft)n Velocity (ft/s)
Time of Conc.
(min)
Pre-Dev. Detention
Basin B
Post-Dev.
Detention Basin B
Post-Dev.
Detention Basin A
Pre-Dev. Detention
Basin A
Pre-Dev. Detention
Basin C
Post-Dev.
Detention Basin C
Project: North Park West
Project #: 21349.03
Date: 06/25/2025
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)00.000 0.95 1 0.95 0.95 0.000
256165 5.881 0.15 1 0.15 0.15 0.8821
0.00 0.00 0
256165 5.881 0.882
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =0.88
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 8.08
5 3.22 2.84
10 2.05 1.81
15 1.58 1.39
20 1.31 1.15
25 1.13 1.00
30 1.00 0.89
35 0.91 0.80
38 0.86 0.76
40 0.83 0.73
45 0.77 0.68
50 0.72 0.64
55 0.68 0.60
60 0.64 0.56
75 0.55 0.49
88 0.50 0.44
90 0.49 0.43
105 0.44 0.39
120 0.41 0.36
150 0.35 0.31
180 0.31 0.28
360 0.20 0.18
720 0.13 0.11
1440 0.08 0.07
1,732.12 ft3 0.76 (ft3 /s)
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
DETENTION BASIN A - PRE-DEVELOPMENT CONDITIONS
Surface Type
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1500C wd x Cf =0.15
Runoff Volume Discharge Volume Site Detention
(ft3 ) (ft3 ) (ft3)484.90 0.00 484.90
851.71 0.00 851.71
1085.56 0.00 1085.56
1251.08 0.00 1251.08
1383.61 0.00 1383.61
1496.00 0.00 1496.00
1594.58 0.00 1594.58
1682.97 0.00 1682.97
1763.49 0.00 1763.49
1732.12 0.00 1732.12
1837.71 0.00 1837.71
1906.74 0.00 1906.74
1971.42 0.00 1971.42
2032.38 0.00 2032.38
2197.48 0.00 2197.48
2342.27 0.00 2342.27
2323.92 0.00 2323.92
2472.12 0.00 2472.12
2590.40 0.00 2590.40
2800.82 0.00 2800.82
2985.37 0.00 2985.37
6181.30 0.00 6181.30
3805.03 0.00 3805.03
4849.75 0.00 4849.75
Project: North Park West
Project #: 21349.03
Date: 02/28/2025
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)00.000 0.95 1 0.95 0.95 0.000
3527345 80.977 0.15 1 0.15 0.15 12.1471
0.00 0.00 0
3527345 80.977 12.147
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =12.15
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 111.28
5 3.22 39.09
10 2.05 24.91
15 1.58 19.14
20 1.31 15.88
25 1.13 13.73
30 1.00 12.20
35 0.91 11.04
40 0.83 10.12
45 0.77 9.37
50 0.72 8.75
55 0.68 8.23
60 0.64 7.77
65 0.61 7.38
68 0.59 7.17
75 0.55 6.72
90 0.49 5.97
105 0.44 5.40
120 0.41 4.95
150 0.35 4.29
180 0.31 3.81
360 0.20 2.43
720 0.13 1.55
1440 0.08 0.99
29,238.77 ft3 7.17 (ft3 /s)
29238.77 0.00 29238.77
28780.65 0.00 28780.65
85115.33 0.00 85115.33
52394.63 0.00 52394.63
66780.13 0.00 66780.13
38566.73 0.00 38566.73
41107.99 0.00 41107.99
34040.60 0.00 34040.60
35669.28 0.00 35669.28
30258.85 0.00 30258.85
32252.68 0.00 32252.68
27146.13 0.00 27146.13
27985.55 0.00 27985.55
25304.94 0.00 25304.94
26255.51 0.00 26255.51
23174.20 0.00 23174.20
24282.98 0.00 24282.98
20599.65 0.00 20599.65
21957.02 0.00 21957.02
17227.13 0.00 17227.13
19052.04 0.00 19052.04
11727.90 0.00 11727.90
14947.93 0.00 14947.93
(ft3 ) (ft3 ) (ft3)6676.99 0.00 6676.99C wd x Cf =0.15
Runoff Volume Discharge Volume Site Detention
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1500
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
DETENTION BASIN B - PRE-DEVELOPMENT CONDITIONS
Surface Type
Project: North Park West
Project #: 21349.03
Date: 06/25/2025
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)00.000 0.95 1 0.95 0.95 0.000
154498 3.547 0.15 1 0.15 0.15 0.5321
0.00 0.00 0
154498 3.547 0.532
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =0.53
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 4.87
5 3.22 1.71
10 2.05 1.09
15 1.58 0.84
20 1.31 0.70
25 1.13 0.60
30 1.00 0.53
35 0.91 0.48
40 0.83 0.44
45 0.77 0.41
46 0.76 0.40
50 0.72 0.38
55 0.68 0.36
60 0.64 0.34
75 0.55 0.29
90 0.49 0.26
105 0.44 0.24
120 0.41 0.22
150 0.35 0.19
180 0.31 0.17
360 0.20 0.11
720 0.13 0.07
1440 0.08 0.04
1,116.92 ft3 0.40 (ft3 /s)
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
DETENTION BASIN C - PRE-DEVELOPMENT CONDITIONS
Surface Type
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.1500C wd x Cf =0.15
Runoff Volume Discharge Volume Site Detention
(ft3 ) (ft3 ) (ft3)292.45 0.00 292.45
513.68 0.00 513.68
654.72 0.00 654.72
754.55 0.00 754.55
834.48 0.00 834.48
902.27 0.00 902.27
961.72 0.00 961.72
1015.03 0.00 1015.03
1063.60 0.00 1063.60
1108.36 0.00 1108.36
1149.99 0.00 1149.99
1116.92 0.00 1116.92
1189.00 0.00 1189.00
1225.77 0.00 1225.77
1325.34 0.00 1325.34
1412.67 0.00 1412.67
1490.98 0.00 1490.98
1562.32 0.00 1562.32
1689.23 0.00 1689.23
1800.53 0.00 1800.53
3728.06 0.00 3728.06
2294.89 0.00 2294.89
2924.97 0.00 2924.97
APPENDIX C Preliminary Post-Development Hydrology Calculations NORTH PARK WESTSIDE
21349.03
Project: North Park West
Project #: 21349.03
Date: 06/25/2025
Design Storm Frequency =10 years
Discharge Rate, d =0.76 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)
24366.33 0.559 0.95 1 0.95 0.95 0.53
231798.6149 5.321 0.15 1 0.15 0.15 0.801
0.00 0.00 01
0.00 0.00 01
0.00 0.00 0
256164.9449 5.8807 1.3296
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =1.33
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 12.18
5 3.22 4.28
10 2.05 2.73
15 1.58 2.10
20 1.31 1.74
25 1.13 1.50
30 1.00 1.34
35 0.91 1.21
40 0.83 1.11
45 0.77 1.03
50 0.72 0.96
55 0.68 0.90
60 0.64 0.85
75 0.55 0.74
90 0.49 0.65
105 0.44 0.59
120 0.41 0.54
150 0.35 0.47
180 0.31 0.42
360 0.20 0.27
720 0.13 0.17
1440 0.08 0.11
1,201.76 ft3 2.10 (ft3 /s)
7310.05 32832.00 -----
9317.10 65664.00 -----
4499.86 8208.00 -----
5735.35 16416.00 -----
3904.52 5472.00 -----
4221.68 6840.00 -----
3530.52 4104.00 -----
3726.23 4788.00 -----
3063.42 2736.00 327.42
3312.27 3420.00 -----
2874.04 2280.00 594.04
2971.53 2508.00 463.53
2658.12 1824.00 834.12
2769.99 2052.00 717.99
2403.51 1368.00 1035.51
2536.75 1596.00 940.75
2085.52 912.00 1173.52
2254.93 1140.00 1114.93
1636.27 456.00 1180.27
1885.76 684.00 1201.76
730.89 45.60 685.29
1283.79 228.00 1055.79
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3 ) (ft3 ) (ft3)= 0.2261C wd x Cf =0.23
Runoff Volume Discharge Volume Site Detention=Pervious
Totals
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN A - POST-DEVELOPMENT CONDITIONS
Surface Type
Project: North Park West
Project #: 21349.03
Date: 02/24/2025
Design Storm Frequency =10 years
Discharge Rate, d =7.17 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)
237305 5.448 0.95 1 0.95 0.95 5.175
3290040 75.529 0.15 1 0.15 0.15 11.3291
0.00 0.00 0
3527345 80.977 16.505
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =16.50
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 151.21
5 3.22 53.12
10 2.05 33.85
15 1.58 26.01
20 1.31 21.57
21 1.27 20.90
22 1.23 20.28
23 1.19 19.70
24 1.16 19.16
25 1.13 18.66
30 1.00 16.58
35 0.91 14.99
40 0.83 13.75
45 0.77 12.73
50 0.72 11.89
55 0.68 11.18
60 0.64 10.56
65 0.61 10.03
75 0.55 9.14
90 0.49 8.12
105 0.44 7.34
120 0.41 6.73
150 0.35 5.82
180 0.31 5.17
17,301.75 ft3 20.28 (ft3 /s)
39107.29 27963.00 11144.29
27185.84
27593.83
9894.60
10324.80
17291.24
17269.03
27990.91 10755.00 17235.91
29835.31 12906.00 16929.31
31489.22
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN B - POST-DEVELOPMENT CONDITIONS
Surface Type
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
Pervious
Totals
= = 0.2038C wd x Cf =0.20
Runoff Volume Discharge Volume Site Detention
(ft3 ) (ft3 ) (ft3)9072.73 430.20 8642.53
15935.94 2151.00 13784.94
20311.32 4302.00 16009.32
23408.31 6453.00 16955.31
25888.00 8604.00 17284.00
15057.00 16432.22
32995.83 17208.00 15787.83
34384.48 19359.00 15025.48
35676.11 21510.00 14166.11
36886.29 23661.00 13225.29
38026.91 25812.00 12214.91
41115.87 32265.00 8850.87
43825.10 38718.00 5107.10
46254.53 45171.00 1083.53
48467.60 51624.00 -----
52404.67 64530.00 -----
55857.75 77436.00 -----
17299.68
17301.75
26333.88
26766.15
9034.20
9464.40
Project: North Park West
Project #: 21349.03
Date: 06/25/2025
Design Storm Frequency =10 years
Discharge Rate, d =0.40 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
ValueA
A/(43560 ft2 /acre)CCfC x Cf C' C' x A
(ft2)(Acres)=(C x Cf ) < or = 1 (Acres)
35558 0.816 0.95 1 0.95 0.95 0.775
118940 2.730 0.15 1 0.15 0.15 0.4101
0.00 0.00 0
154498 3.547 1.185
Weighted Runoff Coefficient, C wdSCjAjSAjC
wd x Cf x SAj =1.19
Where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type jRainfall Rainfall Peak Flow
Duration, t Intensity, i
= Cwd x SAj x i
(min) (in/hr)(ft3 /s)
1 9.16 10.86
5 3.22 3.81
10 2.05 2.43
15 1.58 1.87
20 1.31 1.55
25 1.13 1.34
30 1.00 1.19
35 0.91 1.08
40 0.83 0.99
45 0.77 0.91
50 0.72 0.85
55 0.68 0.80
60 0.64 0.76
75 0.55 0.66
90 0.49 0.58
105 0.44 0.53
120 0.41 0.48
150 0.35 0.42
180 0.31 0.37
360 0.20 0.24
720 0.13 0.15
1440 0.08 0.10
1,422.20 ft3 1.19 (ft3 /s)
6515.28 17280.00 -----
8304.12 34560.00 -----
4010.63 4320.00 -----
5111.79 8640.00 -----
3480.01 2880.00 600.01
3762.69 3600.00 162.69
3146.67 2160.00 986.67
3321.11 2520.00 801.11
2730.36 1440.00 1290.36
2952.15 1800.00 1152.15
2561.57 1200.00 1361.57
2648.46 1320.00 1328.46
2369.12 960.00 1409.12
2468.83 1080.00 1388.83
2142.20 720.00 1422.20
2260.95 840.00 1420.95
1858.78 480.00 1378.78
2009.77 600.00 1409.77
1458.37 240.00 1218.37
1680.73 360.00 1320.73
651.43 24.00 627.43
1144.21 120.00 1024.21
= C wd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3 ) (ft3 ) (ft3)= 0.3341C wd x Cf =0.33
Runoff Volume Discharge Volume Site Detention
Impervious
Pervious
Totals=RATIONAL METHOD FOR RUNOFF CALCULATIONS
BASIN C - POST-DEVELOPMENT CONDITIONS
Surface Type
APPENDIX D O&M PLAN NORTH PARK WESTSIDE
21349.03
February 2025
Project No. 21349.03
STORM DRAINAGE FACILITY MAINTENANCE PLAN
FOR
NORTH PARK WESTSIDE
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 North Park Westside.
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
Bozeman TRAX Partners, LLC
Bozeman TRAX Partners, LLC will own the proposed surface ponds and associated
piping to the proposed ponds until the property is conveyed to the Property Owners
Association.
II. Inspection Thresholds for Cleaning
Surface Pond
If sediment reduces pond volume by 25%, clean pond banks and bottom manually or
mechanically.
III. Cleaning
Surface Pond
P:21349_03_North_Park_Westside_O&M 2 (02/27/25) DME/RPE
To clean the pond manually or mechanically and remove sediment and debris from the
pond banks and bottom.
IV. Inspection, Maintenance, and Replacement Schedule
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
V. Responsible Party
Bozeman TRAX Partners, LLC
Bozeman TRAX Partners, LLC will be responsible for the inspection, maintenance, and
replacement of all stormwater facilities located within the project limits until the
property is conveyed to the Property Owners Association.
I agree to the above inspection, maintenance, and replacement schedule detailed above.
Signature: __________________________________________
Bozeman TRAX Partners, LLC Representative