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INTRODUCTION
The proposed Westside Flats project is a residential multi-family development within an existing
subdivision. The project will include the extensions of May Fly Street and Dragon Fly Street east
into the project to tie into a proposed center drive aisle running north-south, which functions as a
drive access and parking area for the site. Nine buildings are proposed for construction along the
center drive aisle to create 132 – 2 bedroom apartments in a series of 12-plex and 18-plex buildings.
The center drive aisle has proposed perpendicular parking along both sides and has been designed
with a 1.5% cross slope (to the east) instead of a standard crowned design. The center drive aisle
also generally slopes from south to north at the two east-west connection aisles. The stormwater
will be collected in catch curb on the east side of the center drive aisle and perpendicular parking.
The stormwater will flow to a series of inlet curb chases. The curb chases will run to storm swales
that convey water to a set of retention ponds on the east side of the project.
Additional parking areas are also provided along the west side of the property. Generally, these
parking areas are graded to a curb chase on the north side of the parking area, where it is conveyed
to a stormwater retention pond. Stormwater from the parking area at the north end of the project,
in Phase 3, is graded to the north, where it will be conveyed through curb cuts to grass lined storm
swales. The stormwater is then conveyed to Retention Pond #4 and Retention Pond #11, which are
separated from the existing detention pond on the south side of West Babcock Street.
The existing detention pond on the north end of the site is not functioning properly and retains
water permanently. The existing detention pond will not be changed with construction of this
project. A portion of the site to the north will remain landscaped and not contribute any additional
runoff to the existing stormwater infrastructure.
STORM SEWER FACILITIES DESIGN
Storm sewer facilities were sized for the 25-yr storm using Manning’s Equation. For each inlet,
the contributing area, weighted C factor, and time of concentration were calculated. These values
were input into Manning’s Equation to check capacity and flow characteristics for curbs chases,
storm swales, and curb gutters. All curbs are designed to maintain 0.15’ freeboard per C.O.B.
Design Manual Section IV.C.5. For the purposes of this report, each curb chase and swale was
named for the associated drainage areas. Curb chase and storm swale sizing calculations are
included in Appendix C.
RETENTION POND DESIGN
All ponds have been sized according to City of Bozeman Design Standards. The proposed retention
ponds are sized to capture the entire volume of the 10-year, 2-hour storm event. The site lies in an
area of known high groundwater. Appendix D contains groundwater monitoring data from the
Norton Ranch Phase 4 Subdivision. Groundwater Monitoring Well #2 from Norton Ranch Phase
4 is approximately 700 feet from the project site and had minimum groundwater depths of
approximately 3 feet. This information was used to make the assumption that the Seasonal High
Ground Water Level (SHGWL) is greater than 5 feet below existing grade on the site. The
stormwater industry guidance recommends 3 feet minimum separation between stormwater
facilities and the groundwater table. The proposed retention ponds are conservatively designed to
be less than 1.5’ below existing grade to provide approximately 3’ of separation between retention
facilities and the groundwater table.
Calculations used for sizing each pond can be found in Appendix c. Design pond capacities were
calculated using volume surfaces in AutoCAD Civil 3D.
Proposed Retention Pond 1
Retention Pond 1 is located along the western edge of the property in Phase 1 of the project. The
pond receives runoff from the proposed parking lot north of May Fly Street. The runoff is conveyed
via sheet flow and curb and gutter to an outlet chase in the northwest corner of the parking lot. The
required pond volume is 394 cubic feet, and the proposed pond volume is 403 cubic feet. The
proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of Retention Pond 1 is less than 1.5’
below existing grade to avoid the Seasonal High Groundwater Level (SHGWL).
Proposed Retention Pond 2
Retention Pond 2 is located along the western edge of the property in Phase 3 of the project. The
pond receives runoff from the proposed parking lot in the northwest corner of Phase 2 of the project
and proposed landscaped areas in Phase 3. The runoff is conveyed via sheet flow and curb and
gutter to an outlet chase in the northwest corner of the parking lot. The required pond volume is
673 cubic feet, and the proposed pond volume is 843 cubic feet. The proposed pond is 1.5’ deep
with 4:1 side slopes. The bottom of Retention Pond 2 is less than 1.5’ below existing grade to
avoid the Seasonal High Groundwater Level (SHGWL).
Proposed Retention Pond 3
Retention Pond 3 is located along the western edge of the property in Phase 2 of the project. The
pond receives runoff from the proposed Building #6 and the landscaped area behind it. The runoff
will be conveyed via gutters, downspouts and landscaping swales to the pond. The required pond
volume is 339 cubic feet, and the proposed pond volume is 463 cubic feet. The proposed pond is
1.5’ deep with 4:1 side slopes. The bottom of Retention Pond 3 is less than 1.5’ below existing
grade to avoid the Seasonal High Groundwater Level (SHGWL).
Proposed Retention Pond 4
Retention Pond 4 is located on the northwestern part of the project in Phase 3 of the project. The
pond receives runoff from the proposed Building #9, the large parking lot in front of Building 9
and associated landscaping areas. The runoff will be conveyed via gutters, downspouts and curb
chases to the pond. The required pond volume is 2,162 cubic feet, and the proposed pond volume
is 2,487 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of Retention
Pond 4 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater Level
(SHGWL).
Proposed Retention Pond 5
Retention Pond 5 is located along the eastern side of the property in Phase 3 of the project. The
pond receives runoff from the proposed drive aisle, proposed Building #7 and Building #8 and the
landscaped area behind it. The runoff will be conveyed via curb and gutter, a curb chase and a
storm swale to the retention pond. The required pond volume is 2,153 cubic feet, and the proposed
pond volume is 2,259 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom
of Retention Pond 5 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater
Level (SHGWL).
Proposed Retention Pond 6
Retention Pond 6 is located along the eastern side of the property in Phase 2 of the project. The
pond receives runoff from the proposed drive aisle, proposed Building #4 and the landscaped area
behind it, as well as a portion of Building #5. The runoff will be conveyed via curb and gutter, a
curb chase and a storm swale to the retention pond. The required pond volume is 1658 cubic feet,
and the proposed pond volume is 1,939 cubic feet. The proposed pond is 1.5’ deep with 4:1 side
slopes. The bottom of Retention Pond 6 is less than 1.5’ below existing grade to avoid the Seasonal
High Groundwater Level (SHGWL).
Proposed Retention Pond 7
Retention Pond 7 is located along the eastern side of the property in Phase 1 of the project. The
pond receives runoff from the proposed drive aisle, proposed Building #2 and the landscaped area
behind it, as well as a portion of Building #3. The runoff will be conveyed via curb and gutter, a
curb chase and a storm swale to the retention pond. The required pond volume is 1,686 cubic feet,
and the proposed pond volume is 2,079 cubic feet. The proposed pond is 1.5’ deep with 4:1 side
slopes. The bottom of Retention Pond 7 is less than 1.5’ below existing grade to avoid the Seasonal
High Groundwater Level (SHGWL).
Proposed Retention Pond 8
Retention Pond 8 is located along the western side of the property in Phase 1 of the project. The
pond receives runoff from the proposed drive access from May Fly Street, portion of proposed
Building #3 and the landscaped area behind it. The runoff will be conveyed via gutter, landscaping
swales to the retention pond. The required pond volume is 607 cubic feet, and the proposed pond
volume is 639 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of
Retention Pond 8 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater
Level (SHGWL).
Proposed Retention Pond 9
Retention Pond 9 is located along the western side of the property in Phase 1 of the project. The
pond receives runoff from the proposed main drive aisle, the southernmost parking lot, proposed
Building #1 and the landscaped area behind it. The runoff will be conveyed via gutter, landscaping
swales to the retention pond. The required pond volume is 2,024 cubic feet, and the proposed pond
volume is 2,111 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of
Retention Pond 9 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater
Level (SHGWL).
Proposed Retention Pond 10
Retention Pond 10 is located along the eastern side of the property in Phase 2 of the project. The
pond receives runoff from the proposed main drive aisle, the southernmost parking lot, proposed
Building #5 and the landscaped area behind it. The runoff will be conveyed via gutter, landscaping
swales to the retention pond. The required pond volume is 1,391 cubic feet, and the proposed pond
volume is 1,532 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of
Retention Pond 10 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater
Level (SHGWL).
Proposed Retention Pond 11
Retention Pond 11 is located along the northern side of the main parking Aisle in Phase 3 of the
project. The pond receives runoff from the main parking aisle. The runoff will be conveyed via
gutter to the retention pond. The required pond volume is 418 cubic feet, and the proposed pond
volume is 593 cubic feet. The proposed pond is 1.5’ deep with 4:1 side slopes. The bottom of
Retention Pond 11 is less than 1.5’ below existing grade to avoid the Seasonal High Groundwater
Level (SHGWL).
Retention Pond Summary
Pond Drainage Area Pond Depth
(ft)
Required Storage
Volume (cf)
Provided Storage
Volume (cf)
1 1A & 1B 1.5 394 403
2 2A & 2B 1.5 673 843
3 3A 1.5 339 463
4 4A & 4B 1.5 2,162 2,487
5 5A & 5B 1.5 2,153 2,259
6 6A & 6B 1.5 1,658 1,939
7 7A, 7B, & 7C 1.5 1,686 2,079
8 8A & 8B 1.5 607 639
9 9A & 9C 1.5 2,024 2,111
10 10A & 10B 1.5 1,391 1,532
11 11A 1.5 418 593
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APPENDIX A
DRAINAGE AREA MAP
APPENDIX B
DRAINAGE AREA CALULATIONS
DRAINAGE AREA # 1A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 1626 325
Hardscape 0.95 0 0
Total 1626 325
A = Area (acres) 0.04
C = Weighted C Factor 0.20
DRAINAGE AREA # 1B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 205 41
Hardscape 0.95 5732 5445
Total 5937 5486
A = Area (acres) 0.14
C = Weighted C Factor 0.92
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.94 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 99 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.30
Tc Total = 5.00 (5 mimimum)
DRAINAGE AREA # 2A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 2909 582
Hardscape 0.95 326 310
Total 3235 892
A = Area (acres) 0.07
C = Weighted C Factor 0.28
DRAINAGE AREA # 2B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 4219 844
Hardscape 0.95 8631 8200
Total 8631 8200
A = Area (acres) 0.20
C = Weighted C Factor 0.95
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.44 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 70 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.16
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.64%
L = length of gutter (ft) 64
V = mean velocity (ft/s) 2.40
Tc Gutter Flow (minutes) =0.44
Tc Total = 5.00 (5 minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.95 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.20 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 0.72 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0064
Q = PROVIDED GUTTER CAPACITY (cfs) 2.97
DRAINAGE AREA # 3A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 7828 1566
Hardscape 0.95 3611 3430
Total 11439 4996
A = Area (acres) 0.26
C = Weighted C Factor 0.44
DRAINAGE AREA # 4A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 10588 2118
Hardscape 0.95 3612 3431
Total 14200 5549
A = Area (acres) 0.33
C = Weighted C Factor 0.39
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 1.6 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 54 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.17
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0100
L = length of gutter (ft) 184
V = mean velocity (ft/s) 3.00
Tc Gutter Flow (minutes) =1.02
Tc Total = 5.00 (5 minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.39 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.33 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 0.49 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0100
Q = PROVIDED GUTTER CAPACITY (cfs) 3.72
DRAINAGE AREA #4B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 1951 390
Hardscape 0.95 27322 25956
Total 29273 26346
A = Area (acres) 0.67
C = Weighted C Factor 0.90
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 25 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 20 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)0.29
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 5.11 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.20 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 12 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)3.31
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0130
L = length of gutter (ft) 145
V = mean velocity (ft/s) 3.42
Tc Gutter Flow (minutes) =0.71
Tc Total = 5.00 (5 minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.90 (calculated above)
I = 0.78 Tc-0.64 (in/hr)5.75 (25-yr storm)
A = area (acres) 0.67 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 3.48 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0130
Q = PROVIDED GUTTER CAPACITY (cfs) 4.24
DRAINAGE AREA # 5A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 21137 4227
Hardscape 0.95 4815 4574
Total 25952 8801
A = Area (acres) 0.60
C = Weighted C Factor 0.34
DRAINAGE AREA #5B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 3690 738
Hardscape 0.95 23405 22235
Total 27095 22973
A = Area (acres) 0.62
C = Weighted C Factor 0.85
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 25 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 19 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)0.28
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.3 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 75 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.23
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0170
L = length of gutter (ft) 449
V = mean velocity (ft/s) 3.91
Tc Gutter Flow (minutes) =1.91
Tc Total = 5.00 (5 Minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.85 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.62 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 2.02 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0170
Q = PROVIDED GUTTER CAPACITY (cfs) 4.85
DRAINAGE AREA # 6A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 15808 3162
Hardscape 0.95 2337 2220
Total 18145 5381
A = Area (acres) 0.42
C = Weighted C Factor 0.30
DRAINAGE AREA # 6B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 3195 639
Hardscape 0.95 19422 18451
Total 22617 19090
A = Area (acres) 0.52
C = Weighted C Factor 0.84
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.03 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 84 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.35
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0150
L = length of gutter (ft) 133
V = mean velocity (ft/s) 3.67
Tc Gutter Flow (minutes) =0.60
Tc Total = 5.00 (5 Minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.84 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.52 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 1.68 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0150
Q = PROVIDED GUTTER CAPACITY (cfs) 4.55
DRAINAGE AREA # 7A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 3611 3430
Landscape 0.2 11719 2344
Total 15330 5774
A = Area (acres) 0.35
C = Weighted C Factor 0.38
DRAINAGE AREA # 7B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 19357 18389
Landscape 0.2 3609 722
Total 22965 19111
A = Area (acres) 0.53
C = Weighted C Factor 0.83
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.3 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 137 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.66
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0156
L = length of gutter (ft) 57
V = mean velocity (ft/s) 3.74
Tc Gutter Flow (minutes) =0.25
Tc Total = 5.00 (5 Minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.83 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.53 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 1.68 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0156
Q = PROVIDED GUTTER CAPACITY (cfs) 4.64
DRAINAGE AREA # 7C
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Hardscape 0.95 2305 2190
Landscape 0.2 594 119
Total 2899 2309
A = Area (acres) 0.07
C = Weighted C Factor 0.80
DRAINAGE AREA # 8A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 6301 1260
Hardscape 0.95 3611 3430
Total 9912 4691
A = Area (acres) 0.23
C = Weighted C Factor 0.47
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 1.76 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.29 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 277 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)20.13
Tc Total = 20.13
DRAINAGE AREA # 8B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
Landscape 0.2 1769 354
Hardscape 0.95 4123 3917
Total 5892 4271
A = Area (acres) 0.14
C = Weighted C Factor 0.72
DRAINAGE AREA # 9A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
LANDSCAPE 0.2 9760 1952
HARDSCAPE 0.95 2407 2287
Total 12167 4239
A = Area (acres) 0.28
C = Weighted C Factor 0.35
DRAINAGE AREA # 9B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
LANDSCAPE 0.2 6609 1322
HARDSCAPE 0.95 24215 23004
Total 30824 24326
A = Area (acres) 0.71
C = Weighted C Factor 0.79
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 2.4 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 119 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.52
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0178
L = length of gutter (ft) 74
V = mean velocity (ft/s) 4.00
Tc Gutter Flow (minutes) =0.31
Tc Total = 5.00 (5 Minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.79 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.71 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 2.14 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0178
Q = PROVIDED GUTTER CAPACITY (cfs) 4.96
DRAINAGE AREA # 10A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
LANDSCAPE 0.2 2602 520
HARDSCAPE 0.95 15287 14522
Total 17888 15043
A = Area (acres) 0.41
C = Weighted C Factor 0.84
2. Calculate Tc (Time to Concentration)
Tc Overland Flow
Tc = 1.87 (1.1-CCf)D1/2/S1/3
Storm
S = Slope of Basin (%) 1.7 Return (yrs)Cf
C = Rational Method Runoff Coefficient 0.95 2 to 10 1
Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1
D = Length of Basin (ft) 120 26 to 50 1.2
51 to 100 1.25
Tc Overland Flow (minutes)1.72
Tc Gutter Flow
Tc = L/V/60
V = (1.486/n)R2/3 S1/2
n = Mannings Coefficient 0.013
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0100
L = length of gutter (ft) 119
V = mean velocity (ft/s) 3.00
Tc Gutter Flow (minutes) =0.66
Tc Total = 5.00 (5 Minimum)
3. Calculate Flow (Rational Formula)
Q = CIA
C = Weighted C Factor 0.84 (calculated above)
I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm)
A = area (acres) 0.41 (calculated above)
Q = REQUIRED GUTTER CAPACITY (cfs) 1.32 (assuming no carry flow)
PROVIDED GUTTER CAPACITY
1. Calculate Gutter Capacity @ 0.15' Below Top of Curb
Q = (1.486/n)AR2/3 S1/2
n = Mannings Coefficient 0.013
A = Area (ft2)1.24 (0.15' below top of curb)
P = Wetted perimeter (ft) 9.23 (0.15' below top of curb)
R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb)
S = slope (ft/ft) 0.0100
Q = PROVIDED GUTTER CAPACITY (cfs) 3.72
DRAINAGE AREA # 10B
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
LANDSCAPE 0.2 16010 3202
HARDSCAPE 0.95 2407 2287
Total 18418 5489
A = Area (acres) 0.42
C = Weighted C Factor 0.30
DRAINAGE AREA # 11A
1. Calculate Area and Weighted C Factor
Contributing Area C Area (ft 2 )C * Area
LANDSCAPE 0.2 1647 329
HARDSCAPE 0.95 6151 5844
Total 7798 6173
A = Area (acres) 0.18
C = Weighted C Factor 0.79
APPENDIX C
POND SIZING AND STORM SEWER
FACILITIES CALCULATIONS
RETENTION POND #1
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 1A 0.20 1626 325
Hardscape 1A 0.95 0 0
Landscape 1B 0.20 205 41
Hardscape 1B 0.95 5732 5445
Total 7562 5811
C=Weighted C Factor 0.77
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.77
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.17
Q = runoff (cfs) 0.05
V = REQUIRED VOL (ft3)394
Pond Storage Volume (ft3)403
CHASE 1 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 1A 0.20 1626 325
Hardscape 1A 0.95 0 0
Landscape 1B 0.20 205 41
Hardscape 1B 0.95 5732 5445
Total 7562 5811
A = Area (acres) 0.17
C = Weighted C Factor 0.77
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #1B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.77 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.17 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 0.51
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #1
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #2
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 2A 0.20 2909 582
Hardscape 2A 0.95 326 310
Landscape 2B 0.20 4218.70 843.74
Hardscape 2B 0.95 8631 8200
Total 16085 9935
C=Weighted C Factor 0.62
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.62
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.37
Q = runoff (cfs) 0.09
V = REQUIRED VOL (ft3)673
Pond Storage Volume (ft3)843
CHASE 2 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 2A 0.20 2909 582
Hardscape 2A 0.95 326 310
Landscape 2B 0.20 4219 844
Hardscape 2B 0.95 8631 8200
Total 16085 9935
A = Area (acres) 0.37
C = Weighted C Factor 0.62
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #2B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.62 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.37 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 0.87
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #2
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #3
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 3A 0.20 7828 1566
Hardscape 3A 0.95 3611 3430
Total 11439 4996
C=Weighted C Factor 0.44
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.44
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.26
Q = runoff (cfs) 0.05
V = REQUIRED VOL (ft3)339
Pond Storage Volume (ft3)463
RETENTION POND #4
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft2 )C * Area
Landscape 4A 0.20 10588 2118
Hardscape 4A 0.95 12393 11773
Landscape 4A 0.20 1951 390
Hardscape 4A 0.95 18541 17614
Total 43474 31895
C=Weighted C Factor 0.73
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.73
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 1.00
Q = runoff (cfs) 0.30
V = REQUIRED VOL (ft3)2162
Pond Storage Volume (ft3)2,487
CHASE 4A 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 4A 0.20 10588 2118
Hardscape 4A 0.95 12393 11773
Landscape 4B 0.20 1951 390
Hardscape 4B 0.95 18541 17614
Total 43474 31895
A = Area (acres) 1.00
C = Weighted C Factor 0.73
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #4A)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.73 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 1.00 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 2.80
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #4A
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1.5
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.75 2.50 0.30 6.27 4.71 6.27 4.71 T = 1.50
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Swale #4A
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 4
Mannings Formula z (sideslope)= 4
w (btm width, ft)= 0
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.75
R = A/P S (slope, ft/ft) 0.08
A = cross sectional area n low =0.035
P= wetted perimeter n high =0.035
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.75 2.25 6.18 0.36 6.12 13.77 6.12 13.77 T = 6.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
CHASE 4B 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 4B 0.20 1951 390
Hardscape 4B 0.95 18541 17614
Total 20492 18005
A = Area (acres) 0.47
C = Weighted C Factor 0.88
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #4B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.88 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.47 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 1.58
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #4B
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #5
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor (Post-Development)
Contributing Area DA C Area (ft2 )C * Area
Landscape 5A 0.2 21137 4227
Hardscape 5A 0.95 4815 4574
Landscape 5B 0.2 3690 738
Hardscape 5B 0.95 23405 22235
Total 53046 31774
C=Weighted C Factor 0.60
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.60
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 1.22
Q = runoff (cfs) 0.30
V = REQUIRED VOL (ft3)2153
Pond Storage Volume (ft3)2,259
CHASE 5 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 5A 0.20 21137 4227
Hardscape 5A 0.95 4815 4574
Landscape 5B 0.20 3690 738
Hardscape 5B 0.95 23405 22235
Total 53046 31774
A = Area (acres) 1.22
C = Weighted C Factor 0.60
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #5B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.60 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 1.22 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 2.79
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #5
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Swale #5
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 4
Mannings Formula z (sideslope)= 4
w (btm width, ft)= 0
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.025
A = cross sectional area n low =0.035
P= wetted perimeter n high =0.035
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 1.00 4.12 0.24 2.61 2.61 2.61 2.61 T = 4.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #6
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 6A 0.20 15808 3162
Hardscape 6A 0.95 2337 2220
Landscape 6B 0.20 3195 639
Hardscape 6B 0.95 19422 18451
Total 40761 24471
C=Weighted C Factor 0.60
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.60
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.94
Q = runoff (cfs) 0.23
V = REQUIRED VOL (ft3)1658
Pond Storage Volume (ft3)1,939
CHASE 6 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 6A 0.20 15808 3162
Hardscape 6A 0.95 2337 2220
Landscape 6B 0.20 3195 639
Hardscape 6B 0.95 19422 18451
Total 40761 24471
A = Area (acres) 0.94
C = Weighted C Factor 0.60
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #5B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.60 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.94 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 2.15
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #6
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #7
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft2 )C * Area
Hardscape 7A 0.95 3611 3430
Landscape 7A 0.2 11719 2344
Hardscape 7B 0.95 19357 18389
Landscape 7B 0.2 3609 722
Hardscape 7C 0.95 2305 2190
Landscape 7C 0.2 594 119
Total 38295 24885
C=Weighted C Factor 0.65
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.65
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.88
Q = runoff (cfs) 0.23
V = REQUIRED VOL (ft3)1686
Pond Storage Volume (ft3)2,079
CHASE 7 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Hardscape 7A 0.95 3611 3430
Landscape 7A 0.2 11719 2344
Hardscape 7B 0.95 19357 18389
Landscape 7B 0.2 3609 722
Hardscape 7C 0.95 2305 2190
Landscape 7C 0.2 594 119
Total 38295 24885
A = Area (acres) 0.88
C = Weighted C Factor 0.65
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #7B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.65 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.88 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 2.19
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #7
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Swale #7
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 4
Mannings Formula z (sideslope)= 4
w (btm width, ft)= 0.5
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.0097
A = cross sectional area n low =0.035
P= wetted perimeter n high =0.035
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 1.25 4.62 0.27 1.75 2.19 1.75 2.19 T = 4.50
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #8
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 8A 0.20 6301 1260
Hardscape 8A 0.95 3611 3430
Landscape 8B 0.20 1769 354
Hardscape 8B 0.95 4123 3917
Total 15804 8961
C=Weighted C Factor 0.57
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.57
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.36
Q = runoff (cfs) 0.08
V = REQUIRED VOL (ft3)607
Pond Storage Volume (ft3)639
CHASE 8 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
Landscape 8A 0.2 6301 1260
Hardscape 8A 0.95 3611 3430
Landscape 8B 0.2 1769 354
Hardscape 8B 0.95 4123 3917
Total 15804 8961
A = Area (acres) 0.36
C = Weighted C Factor 0.57
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.34 (DA #8A)
i = rainfall intensity (in./hr.) 1.57
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.57 (calculated above)
i = rainfall intensity (in./hr.) 1.57 (calculated above)
A = Area (acres) 0.36 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 0.32
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #8
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #9
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
LANDSCAPE 9A 0.20 9760 1952
HARDSCAPE 9A 0.95 2407 2287
LANDSCAPE 9B 0.20 6609 1322
HARDSCAPE 9B 0.95 24215 23004
Total 42991 28565
C=Weighted C Factor 0.66
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.66
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.99
Q = runoff (cfs) 0.27
V = REQUIRED VOL (ft3)1936
Pond Storage Volume (ft3)2,111
CHASE 9 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
LANDSCAPE 9A 0.2 9760 1952
HARDSCAPE 9A 0.95 2407 2287
LANDSCAPE 9B 0.2 6609 1322
HARDSCAPE 9B 0.95 24215 23004
Total 42991 28565
A = Area (acres) 0.99
C = Weighted C Factor 0.66
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #9B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.66 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.99 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 2.51
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Chase #9
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Swale #9
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 4
Mannings Formula z (sideslope)= 4
w (btm width, ft)= 0
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.75
R = A/P S (slope, ft/ft) 0.005
A = cross sectional area n low =0.035
P= wetted perimeter n high =0.035
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.75 2.25 6.18 0.36 1.53 3.44 1.53 3.44 T = 6.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #10
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
LANDSCAPE 10A 0.20 2602 520
HARDSCAPE 10A 0.95 15287 14522
LANDSCAPE 10B 0.20 16010 3202
HARDSCAPE 10B 0.95 2407 2287
Total 36306 20532
C=Weighted C Factor 0.57
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.57
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.83
Q = runoff (cfs) 0.19
V = REQUIRED VOL (ft3)1391
Pond Storage Volume (ft3)1,532
CHASE 10 25-YR OUTFLOW RATE
REQUIRED CAPACITY
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft 2 )C * Area
LANDSCAPE 10A 0.2 2602 520
HARDSCAPE 10A 0.95 15287 14522
LANDSCAPE 10B 0.2 16010 3202
HARDSCAPE 10B 0.95 2407 2287
Total 36306 20532
A = Area (acres) 0.83
C = Weighted C Factor 0.57
2. Calculate Rainfall Intensity (Duration = Max Tc from Contributing Drainage Areas)
i = 0.78x-0.64 (25-yr Storm, Fig. I-3, COB Design Standards)
x = storm duration (hrs) 0.08 (DA #10B)
i = rainfall intensity (in./hr.) 3.83
3. Calculate 25-yr Pond Outflow Rate
Q = CiA
C = Rational Method Runoff Coefficient 0.57 (calculated above)
i = rainfall intensity (in./hr.) 3.83 (calculated above)
A = Area (acres) 0.83 (calculated above)
Q = 25-yr Pipe Flow Rate (cfs) 1.80
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Curb #10
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 0
Mannings Formula z (sideslope)= 0
w (btm width, ft)= 1
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.5
R = A/P S (slope, ft/ft) 0.015
A = cross sectional area n low =0.013
P= wetted perimeter n high =0.013
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.5 0.50 2.00 0.25 5.56 2.78 5.56 2.78 T = 1.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
MANNING'S EQUATION for OPEN CHANNEL FLOW Storm Swale #10
Project: Westside Flats Location: Bozeman, MT
By: AMK Date: 5/19/2020
Chk By: Date:
INPUT
z (sideslope)= 4
Mannings Formula z (sideslope)= 4
w (btm width, ft)= 0
Q = (1.486/n)ARh2/3S1/2 d (depth, ft)= 0.75
R = A/P S (slope, ft/ft) 0.0075
A = cross sectional area n low =0.035
P= wetted perimeter n high =0.035
S = slope of channel V = (1.49/n)Rh2/3S1/2
n = Manning's roughness coeffiQ = V x A
Depth, ft Area, sf
Wetted
Perimete
r, ft
Hydraulic
Radius, ft Velocity, fps Flow, cfs
Velocity,
fps Flow, cfs
0.75 2.25 6.18 0.36 1.87 4.22 1.87 4.22 T = 6.00
Low N High N
d
w
z
11
z
T
Clear Data
Entry Cells
RETENTION POND #11
REQUIRED VOLUME
1. Calculate Area and Weighted C Factor
Contributing Area DA C Area (ft2 )C * Area
Landscape 11A 0.20 1647 329
Hardscape 11A 0.95 6151 5844
Total 7798 6173
C=Weighted C Factor 0.79
2. Calculate Required Volume
Q = CIA
V=7200Q
C = Weighted C Factor 0.79
I = intensity (in/hr) 0.41 (10 yr, 2hr storm)
A = Area (acres) 0.18
Q = runoff (cfs) 0.06
V = REQUIRED VOL (ft3)418
Pond Storage Volume (ft3)593
APPENDIX D
GROUNDWATER MONITORING DATA
FALLON STREETWATER LILY DRIVEMAY FLY STREETDRAGON FLY STREETWSF SITE
Project Engineer:Matt H
Project:
Well Information:bgs = below ground surface ags = above ground surface
MW-1 MW-2 MW-3 MW-4
10'10'10'10'
0.58 1.71 0.71 0.92
Groundwater Information:
MW-1 MW-2 MW-3 MW-4
02/14/18 6.81 6.29 4.20 4.38
03/13/18 6.94 6.39 4.20 4.34
04/13/18 6.10 5.10 3.12 3.30
05/11/18 6.87 6.36 4.20 4.35
05/25/18 6.78 6.18 4.14 4.31
06/08/18 6.99 6.62 4.37 4.54
06/22/18 6.30 6.51 4.48 4.60
07/06/18 8.64 8.21 5.91 6.10
07/20/18 7.49 7.32 4.85 5.10
08/03/18 7.47 7.32 4.85 5.21
08/17/18 7.57 7.10 5.00 5.21
08/30/18 7.15 6.82 4.50 4.70
09/14/18 7.25 6.85 4.65 4.80
Monitor Well Data
Project Number:161140
Norton East Ranch Subdivision, Phase 4
Project Location:Bozeman
Well ID
Well Depth (feet-bgs)
Top of Well (feet-ags)
Date Depth to Ground Water (feet-bgs)
BB+z z2:1 Δσ EtBqH DCompressible soil layerRigid soil layer