HomeMy WebLinkAbout20 - Design Report - Four Points Ph II - Stormwater
STORMWATER DESIGN REPORT
FOR:
FOUR POINTS PHASE 2 SUBDIVISION
BOZEMAN, MT
Prepared By:
Madison Engineering
895 Technology Blvd Ste 203
Bozeman, MT 59718
(406) 586-0262
OCTOBER 2020
FOUR POINTS PHASE 2 SUBDIVISION
STORMWATER DESIGN REPORT
A. Introduction
The proposed development for the Four Points Phase 2 Subdivision is located within the SE
¼ of Section 34, Township 1 S, Range 5 E in the City of Bozeman Montana. The
development is an expansion of the Four Points Phase 1 development. The developed area in
Phase 2 will be approximately 13.79 acres, which is zoned for high density residential (R-4)
development, and approximately 22.57 acres dedicated to wetland areas or common open
space areas. Phase 2 includes the construction of two local City streets, Veronica Way from
Cattail St to Kimberwicke St and extending existing Blondie St to Veronica Way.
This report includes a description of the proposed stormwater management facilities and their
design parameters. The report provides a stormwater plan, basin delineation, runoff
calculations, conveyance structure sizing, and detention pond recommendations for the
project. This Phase 2 report is in accordance with the previous stormwater reports that have
been submitted for the Phase 1 development.
The following references were used in the preparation of this report:
a. COB Design Standards and Specifications Policy, 2004 (DSSP). Addendum #7
b. COB Modifications to Montana Public Works Standard Specifications (MPWSS)
c. Four Points Phase 1 Subdivision Stormwater calculations (2014)
d. Milkhouse Ave & Blondie St Stormwater Design Report (2014)
The Four Points Subdivision is shown on the in the figure below:
B. Existing Site Conditions
The Four Points subdivision lies in northwest Bozeman, contains delineated wetlands which
have been declared restricted wetland and common open space areas, and has slopes falling
northward between 1% and 2%. There are no delineated floodplains in the subdivision. A
geotechnical report was conducted for the entire Four Points Phase 2 Development in 2015
by Allied Engineering. In general, soil conditions consist of a layer of topsoil 1.0 to 3.5 ft
thick followed by a layer of silts and clays between 3.0 and 13.5 ft depths, followed by
alluvial sandy gravel. Groundwater was monitored on the site and seasonal high
groundwater levels were observed between 2 and 5 ft below the existing surface. It is
anticipated that significant dewatering efforts will be required for utility construction.
However, to date groundwater has not been observed in the existing stormwater ponds or
infrastructure.
A significant portion of the subdivision is delineated wetlands. During phase 1 construction,
culvert crossings were provided under the roadways for the wetland areas. The proposed
Phase 2 road improvements do not include additional culvert crossings.
There are three existing stormwater detention basins on the site which will be utilized for the
Phase 2 infrastructure. These detention ponds have been in place for about 5 years and are
well established. Standing water has not been observed in any detention pond. These ponds
were sized during the Phase 1 development and were made large enough to account for
future Phase 2 drainage. These ponds are identified as follows: Park Detention Pond, Cattail
St Detention Pond, and Blondie St Detention Pond.
There are three additional ponds which exist on the site that serve development to the south
including Baxter Meadows Phase 6. At the time of this submittal, no changes are proposed
to these existing ponds. However, it is anticipated that future site development within
proposed Lot 4 Block 3 will require adjustment to the existing pond within that lot.
Additionally, there are existing stormwater pipes and curb inlets which were constructed with
Phase 1 that were sized to serve the Phase 2 areas. These existing pipes and curb inlets will
be utilized to convey runoff from the Phase 2 areas into the existing detention ponds.
The existing stormwater infrastructure, existing detention ponds, delineated basins, and
proposed improvements are displayed on the Stormwater Exhibit and Storm Pipe Exhibit
included in the Appendix.
C. Proposed Improvements
Phase 2 includes the construction of two local City streets, Veronica Way from Cattail St to
Kimberwicke St and extending existing Blondie St to Veronica Way. The Phase 2
subdivision establishes five developable lots that will drain into existing stormwater
infrastructure via existing stormwater main pipe stubs or curb and gutter. The runoff then
flows into one of the three existing detention ponds, which were sized to accommodate the
Phase 2 development areas.
The improvements include modification of the existing pond outfall structures to provide
retention for the first 0.5” of rainfall per City requirements, as described herein. The existing
stormwater infrastructure, existing detention ponds, delineated basins, and proposed
improvements are displayed on the Stormwater Exhibit and Storm Pipe Exhibit included in
the Appendix.
D. Peak Flow (Runoff) Calculations
Basins were delineated for the entire Four Points Subdivision as shown on the attached
Stormwater Exhibit. The City of Bozeman design standards were utilized to estimate the
peak runoffs for the 25-year event with the rational method. Runoff C coefficients were
estimated for each basin in accordance with City design standards. A C coefficient of 0.65
was used for the developable lots. The peak runoffs are summarized in the table below,
detailed calculations are included in the appendix:
Drainage
Area No.
Area
(Ac.) Weighted C
25 Yr
Q (cfs) Drains to:
A 1.26 0.67 1.19 Park Pond
B 5.36 0.20 0.98 Park Pond
C 1.25 0.74 1.66 Park Pond
D 1.62 0.65 1.77 Blondie Pond
E 5.52 0.65 5.83 Blondie Pond
F 1.92 0.74 2.34 Blondie Pond
G 2.68 0.65 3.31 Cattail Pond
H 2.40 0.67 1.95 Cattail Pond
I 3.05 0.65 3.85 Cattail Pond
J 0.95 0.74 1.41 Cattail Pond
K 6.83 0.65 6.44 Cattail Pond
E. Conveyance Capacity
Runoff from the basins flows into curb and gutter, then into existing curb inlets, and into
existing stormwater piping. The curb, gutter, existing inlet, and existing pipe locations are
displayed on the Storm Pipe Exhibit in the Appendix. The existing pipes were checked to
ensure that they have capacity for the 25 year peak flows. A summary of the pipe size, slope,
inflow, and capacity is shown in the table below:
Pipe Contributing Basin Inflow Q(25) (cfs) Pipe Size Pipe Slope Pipe Capacity (cfs)
EX Pipe 1 A 1.19 15" 0.50% 7.1
EX Pipe 2 D 1.77 15" 0.50% 7.1
EX Pipe 3 C, D 3.42 15" 0.50% 7.1
EX Pipe 4 A, B, C, D 5.59 18" 0.50% 11.5
EX Pipe 5 E, F, G 11.48 18" 0.50% 11.5
EX Pipe 6 K 6.44 18" 0.50% 11.5
EX Pipe 7 H, J, K 9.80 18" 0.50% 11.5
EX Pipe 8 H, I, J, K 13.66 24" 0.50% 24.8
The existing pipes have the capacity to handle the 25 year peak flows. Detailed pipe
conveyance calculations are included in the Appendix.
The existing and proposed curb & gutter and existing curb inlets were also checked for
capacity and found to be adequate. For the existing curb inlets, both weir and orifice flow
were considered. Three of the existing inlets are located at sag points on the existing
roadways, which act as orifice flow. The remaining existing inlets are not at sag locations, so
weir flow is appropriate. Detailed curb & gutter and curb inlet conveyance calculations are
included in the Appendix.
F. Stormwater Detention & Treatment
Stormwater runoff is directed into three existing detention pond facilities, the Park pond, the
Cattail St pond, and the Blondie St pond. These ponds were constructed in 2015 without
consideration for the retention of the first 0.5” of rainfall per city standards. Therefore, slight
modifications are proposed to the existing pond outfall structures to retain the first 0.5” of
rainfall. This allows for the first 0.5” of rainfall on impervious areas to be retained in the
pond for treatment prior to release. The modifications to the outfall structures consist of
widening the outfall slot width, grouting or blocking off a portion of the existing bottom of
the slot, and in the case of the Blondie St pond, raising the outfall structure. The modified
outfall slot widths were sized to reduce the pond outflow rate to the pre-development flow
rates. Additionally, the total pond volumes were checked to ensure that they are still
adequate with the adjusted outfall structure configurations. Per City of Bozeman Standards,
the maximum pond depth at the overflow is between 1.5’ and 2.5’. The pond volumes,
maximum depths, and proposed slot widths are summarized in the table below:
Pond
Identification
Proposed
Volume at
Overflow
(cf)
Proposed 0.5"
Storm
Retention
Volume (cf)
Pond Depth
at Overflow
(ft)
Proposed
Slot Width
(ft)
Park Pond 6,981 2,598 1.5 0.49
Cattail St 19,039 4,996 1.5 0.54
Blondie St 10,265 3,453 2.0 0.49
The stormwater ponds, outfall structures, and contributing basins are displayed in the
attached Stormwater System Exhibit. Detailed calculations for pond sizing, outfall sizing,
and retention volume for the 0.5” of rainfall are included in the Appendix.
G. Stormwater Maintenance Plan
The proposed storm drainage facilities will be privately operated and maintained by the
Property Owner. A stormwater maintenance plan that describes maintenance operations and
procedures is included in the Appendix. The property covenants should include these
stormwater maintenance provisions.
Appendices
A. Exhibits
B. Runoff Calculations
C. Conveyance Calculations
D. Detention Facility Calculations
E. Stormwater Maintenance Plan
Appendix A:
Exhibits
PROPOSED
LOT 1 BLK 2
70,767 SF
1.62 ACRES
PROPOSED
LOT 2 BLK 2
179,501 SF
4.121 ACRES
(WETLANDS)
PROPOSED
LOT 1
BLK 1
75,992 SF
1.74 ACRES
(WETLANDS)
PROPOSED
LOT 4 BLK 3
78,120 SF
1.79 ACRES
PROPOSED
LOT 6 BLK 3
487,175 SF
11.18 ACRES
(WETLANDS)
EXISTING LOT 1
MINOR SUB 475
PUBLIC PARK
233,438 SF
5.359 ACRES
ZONING: R3
PROPOSED
COMMON OPEN SPACE
LOT 5 BLK 3
24,009 SF, 0.55 ACRES
(Detention Basin)
PROPOSEDLOT 7 BLK 372,136 SF1.66 ACRES
(LINEAR PARK)
PROPOSED
COMMON OPEN SPACE
LOT 3 BLK 2
30,430 SF, 0.70 ACRES
(Detention Basin)
PROPOSED
LOT 1 BLK3
9,914 SF
0.23 ACRES
(Lift Station)VERONICA WAYBLONDIE STREET
CATTAIL STREET
KIMBERWICKE STREETMILKHOUSE AVEVAQUERO WAYCASPIAN AVEDAVIS LANEFERGUSON AVEKIMBERWICKE STREET
EXISTING LOT 2
MINOR SUB 475
115,826 SF
2.659 ACRES
ZONING: R3
EXISTING LOT 3MINOR SUB 475123,623 SF2.838 ACRES
ZONING: R4
PROPOSEDLOT 4 BLK 2132,995 SF
3.05ACRES
PROPOSED
LOT 2 BLK 1
116,759 SF
2.68 ACRES
PROPOSEDLOT 3 BLK 3
101,002 SF
2.32 ACRES
PROPOSED
LOT 2 BLK 3
101,437 SF
2.33 ACRES
GREENWAY BLVDBASIN H
2.40 ACRES
C = 0.67
BASIN A
1.26 ACRES
C = 0.67
BASIN C
1.26 ACRES
C = 0.74
BASIN F
1.92 ACRES
C = 0.74
BASIN J
0.95 ACRES
C = 0.74
BASIN D
1.62 ACRES
C = 0.65BASIN B
5.36 ACRES
C = 0.2
BASIN E
5.52 ACRES
C = 0.65
BASIN G
2.68 ACRES
C = 0.65
BASIN I
3.05 ACRES
C = 0.65
BASIN K
6.83 ACRES
C = 0.65
LEGEND
1" =
0
SCALE
100'
20050100
EXHIBITMADISON ENGINEERING
895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718
PHONE (406) 586-0262
FOUR POINTS PHASE 2
STORMWATER EXHIBIT
PROPOSED
LOT 1 BLK 2
70,767 SF
1.62 ACRES
PROPOSED
LOT 2 BLK 2
179,501 SF
4.121 ACRES
(WETLANDS)
PROPOSED
LOT 1
BLK 1
75,992 SF
1.74 ACRES
(WETLANDS)
PROPOSED
LOT 4 BLK 3
78,120 SF
1.79 ACRES
PROPOSED
LOT 6 BLK 3
487,175 SF
11.18 ACRES
(WETLANDS)
EXISTING LOT 1
MINOR SUB 475
PUBLIC PARK
233,438 SF
5.359 ACRES
ZONING: R3
PROPOSED
COMMON OPEN SPACE
LOT 5 BLK 3
24,009 SF, 0.55 ACRES
(Detention Basin)
PROPOSEDLOT 7 BLK 372,136 SF1.66 ACRES
(LINEAR PARK)
PROPOSED
COMMON OPEN SPACE
LOT 3 BLK 2
30,430 SF, 0.70 ACRES
(Detention Basin)
PROPOSED
LOT 1 BLK3
9,914 SF
0.23 ACRES
(Lift Station)VERONICA WAYBLONDIE STREET
CATTAIL STREET
KIMBERWICKE STREETMILKHOUSE AVEVAQUERO WAYCASPIAN AVEDAVIS LANEFERGUSON AVEKIMBERWICKE STREET
EXISTING LOT 2
MINOR SUB 475
115,826 SF
2.659 ACRES
ZONING: R3
EXISTING LOT 3MINOR SUB 475123,623 SF2.838 ACRES
ZONING: R4
PROPOSEDLOT 4 BLK 2132,995 SF
3.05ACRES
PROPOSED
LOT 2 BLK 1
116,759 SF
2.68 ACRES
PROPOSEDLOT 3 BLK 3
101,002 SF
2.32 ACRES
PROPOSED
LOT 2 BLK 3
101,437 SF
2.33 ACRES
GREENWAY BLVDLEGEND
1" =
0
SCALE
100'
20050100
EXHIBITMADISON ENGINEERING
895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718
PHONE (406) 586-0262
FOUR POINTS PHASE 2
STORM PIPE EXHIBIT
Appendix B:
Runoff Calculations
Drainage Area No.Area (Ac.) Weighted C 100 Yr 25 Yr 10 Yr Drains to:
A 1.26 0.67 1.95 1.19 0.88 Park Pond
B 5.36 0.20 1.31 0.98 0.80 Park Pond
C 1.25 0.74 3.08 1.66 1.19 Park Pond
D 1.62 0.65 2.88 1.77 1.33 Blondie Pond
E 5.52 0.65 9.51 5.83 4.37 Blondie Pond
F 1.92 0.74 4.34 2.34 1.67 Blondie Pond
G 2.68 0.65 5.43 3.31 2.49 Cattail Pond
H 2.40 0.67 3.19 1.95 1.44 Cattail Pond
I 3.05 0.65 6.34 3.85 2.90 Cattail Pond
J 0.95 0.74 2.65 1.41 1.02 Cattail Pond
K 6.83 0.65 10.44 6.44 4.82 Cattail Pond
General Equation:i = a/(b+D)n where D is duration in hours, i = intensity in inches/hour
Design Rainfall Freq.100 25 10
IDF coefficient a 1.01 0.78 0.64
IDF coefficient b 0 0 0
IDF coefficient n 0.67 0.64 0.65
Adjustment Factor Cf:1.25 1.1 1
60' ROW
Cross-sectional
dist (ft)C
Landscaped 15 0.2
Paved (road&sidewalk)45 0.9
Total 60 0.73
65' ROW
Cross-sectional
dist (ft)C
Landscaped 15 0.2
Paved (road&sidewalk)50 0.9
Total 65 0.74
Four Points Phase 2
Peak Flow Summary (cfs)
Storm Information
IDF Equations from Bozeman Stormwater Master Plan for City of Bozeman, March 1982
Weighted C Value - Local Streets (60' ROW)
Peak flow calculations
See SD1.2 for visual reference
Drainage Areas - Post Development
Weighted C Value - Local Streets (65' ROW)
Page 1 of 5
60' ROW
Cross-sectional
dist (ft)C
Landscaped 14 0.2
Paved (road&sidewalk)46 0.9
Total 60 0.74
Cross-sectional
dist (ft)C
Landscaped 15 0.2
Paved (road&sidewalk)30 0.9
Total 45 0.67
Estimated based on R-4 Zoning
C = 0.65
Drainage Area A Area C
1.26 acres 0.67
Total 1.26 acres
0.67
1.00 percent
1200 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.83 0.73 0.67 (Shall not exceed 1.00)
Total tc:17.27 23.75 28.07 minutes
intensity at tc 2.33 1.41 1.05 in/hr
2.0 1.2 0.9 cfs
Drainage Area B Area C
5.36 acres 0.20
Total 5.36 acres
0.20
1.00 percent
800 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.25 0.22 0.20 (Shall not exceed 1.00)
Total tc:44.96 46.54 47.60 minutes
intensity at tc 1.23 0.92 0.74 in/hr
1.3 1.0 0.8 cfs
Drainage Area C Area C
1.25 acres 0.74
Total 1.25 acres
0.74
1.00 percent
Travel Distance 900 feet
Design Rainfall Freq. 100 25 10 years
Weighted C
Weighted C Value - Milkhouse Ave (60' ROW)
Cattail & Ferguson
Weighted C Value - Lot-Side Half of Ferguson & Cattail
Weighted C Value - Developable Lots
Travel Distance
Peak Q values
Average slope
Average slope
Travel Distance
Weighted C
Average slope
peak runoff:
Milkhouse 60' R.O.W.
Existing Park
peak runoff:
Weighted C
Page 2 of 5
C*Cf 0.92 0.81 0.74 (Shall not exceed 1.00)
Total tc:10.05 16.25 20.38 minutes
intensity at tc 3.34 1.80 1.29 in/hr
3.1 1.7 1.2 cfs
Drainage Area D Area C
1.62 acres 0.65
Total 1.62 acres
0.65
0.50 percent
400 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.81 0.72 0.65 (Shall not exceed 1.00)
Total tc:13.55 18.14 21.20 minutes
intensity at tc 2.74 1.68 1.26 in/hr
2.9 1.8 1.3 cfs
Drainage Area E Area C
Existing Lot 2 & 3 Minor Sub 475 5.52 acres 0.65
Total 5.52 acres
0.65
1.00 percent
700 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.81 0.72 0.65 (Shall not exceed 1.00)
Total tc:14.22 19.05 22.26 minutes
intensity at tc 2.65 1.63 1.22 in/hr
9.5 5.8 4.4 cfs
Drainage Area F Area C
1.92 acres 0.74
Total 1.92 acres
0.74
1.00 percent
1200 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.92 0.81 0.74 (Shall not exceed 1.00)
Total tc:11.46 18.64 23.42 minutes
intensity at tc 3.06 1.65 1.18 in/hr
4.3 2.3 1.7 cfs
Drainage Area G Area C
Proposd Lot 2 Block 1 (R-4) 2.68 acres 0.65
Total 2.68 acres
0.65
1.25 percent
500 feet
Blondie & Veronica 60' R.O.W.
Weighted C
Weighted C
peak runoff:
Average slope
Weighted C
Travel Distance
Average slope
Average slope
Travel Distance
peak runoff:
Average slope
Travel Distance
peak runoff:
Proposed Lot 1, Block 2 (R-4)
Weighted C
peak runoff:
Travel Distance
Page 3 of 5
Design Rainfall Freq. 100 25 10 years
C*Cf 0.81 0.72 0.65 (Shall not exceed 1.00)
Total tc:11.16 14.94 17.47 minutes
intensity at tc 3.12 1.90 1.43 in/hr
5.4 3.3 2.5 cfs
Drainage Area H Area C
Cattail St 2.40 acres 0.67
Total 2.40 acres
0.67
0.50 percent
1200 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.83 0.73 0.67 (Shall not exceed 1.00)
Total tc:21.76 29.93 35.37 minutes
intensity at tc 1.99 1.22 0.90 in/hr
3.2 1.9 1.4 cfs
Drainage Area I Area C
Proposed Lot 4 Block 2 (R-4) 3.05 acres 0.65
Total 3.05 acres
0.65
1.00 percent
400 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.81 0.72 0.65 (Shall not exceed 1.00)
Total tc:10.75 14.40 16.83 minutes
intensity at tc 3.20 1.94 1.46 in/hr
6.3 3.9 2.9 cfs
Drainage Area J Area C
Veronica Way 65' R.O.W. 0.95 acres 0.74
Total 0.95 acres
0.74
1.40 percent
800 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.92 0.81 0.74 (Shall not exceed 1.00)
Total tc:8.36 13.60 17.09 minutes
intensity at tc 3.78 2.02 1.45 in/hr
2.7 1.4 1.0 cfs
Drainage Area K Area C
6.83 acres 0.65
Total 6.83 acres
0.65
1.00 percent
1000 feet
Average slope
Travel Distance
peak runoff:
Weighted C
Average slope
Travel Distance
Weighted C
Travel Distance
peak runoff:
Weighted C
Average slope
peak runoff:
Travel Distance
Weighted C
Average slope
peak runoff:
This information was
taken from the S. 11th
Improvement project
drainage report ("Basin
J").
Proposed Lots 2, 3, 4 Block 3
Page 4 of 5
Design Rainfall Freq. 100 25 10 years
C*Cf 0.81 0.72 0.65 (Shall not exceed 1.00)
Total tc:17.00 22.77 26.61 minutes
intensity at tc 2.35 1.45 1.09 in/hr
10.4 6.4 4.8 cfspeak runoff:
Page 5 of 5
Appendix C:
Conveyance Calculations
Four Points Phase 2 Subdivision
Stormwater Pipe Capacity Summary
Pipe Contributing Basin
Inflow
Q(25) (cfs)Pipe Size Pipe Slope
Pipe
Capacity (cfs)
EX Pipe 1 A 1.19 15" 0.50% 7.1
EX Pipe 2 D 1.77 15" 0.50% 7.1
EX Pipe 3 C, D 3.42 15" 0.50% 7.1
EX Pipe 4 A, B, C, D 5.59 18" 0.50% 11.5
EX Pipe 5 E, F, G 11.48 18" 0.50% 11.5
EX Pipe 6 K 6.44 18" 0.50% 11.5
EX Pipe 7 H, J, K 9.80 18" 0.50% 11.5
EX Pipe 8 H, I, J, K 13.66 24" 0.50% 24.8
DA Q(25) (cfs)
A 1.19
B 0.98
C 1.66
D 1.77
E 5.83
F 2.34
G 3.31
H 1.95
I 3.85
J 1.41
K 6.44
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =15.0 Enter Value
Diameter,do (ft) =1.25
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft
2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.06 0.90 0.02 0.56 0.04 0.54 0.04 0.00 0.0 14.2 6825.4 1.4 0.03
0.13 1.29 0.06 0.80 0.08 0.75 0.09 0.02 0.1 61.8 29674.5 2.2 0.07
0.19 1.59 0.12 0.99 0.12 0.89 0.13 0.04 0.3 143.9 69090.5 2.8 0.12
0.25 1.85 0.17 1.16 0.15 1.00 0.17 0.07 0.6 259.3 124468.8 3.3 0.17
0.31 2.09 0.24 1.31 0.18 1.08 0.22 0.11 0.9 405.6 194698.0 3.8 0.22
0.38 2.32 0.31 1.45 0.21 1.15 0.27 0.16 1.3 579.9 278343.1 4.2 0.27
0.44 2.53 0.38 1.58 0.24 1.19 0.32 0.22 1.7 778.6 373727.5 4.5 0.32
0.50 2.74 0.46 1.71 0.27 1.22 0.37 0.28 2.2 997.9 478974.9 4.9 0.37
0.56 2.94 0.54 1.84 0.29 1.24 0.43 0.35 2.7 1233.4 592031.1 5.1 0.41
0.63 3.14 0.61 1.96 0.31 1.25 0.49 0.43 3.3 1480.6 710671.1 5.4 0.45
0.69 3.34 0.69 2.09 0.33 1.24 0.56 0.52 3.9 1734.4 832495.6 5.6 0.48
0.75 3.54 0.77 2.22 0.35 1.22 0.63 0.61 4.4 1989.4 954914.8 5.8 0.52
0.81 3.75 0.84 2.34 0.36 1.19 0.71 0.71 5.0 2239.8 1075115.2 5.9 0.54
0.88 3.96 0.92 2.48 0.37 1.15 0.80 0.82 5.5 2479.2 1190001.2 6.0 0.56
0.94 4.19 0.99 2.62 0.38 1.08 0.91 0.94 6.0 2700.2 1296090.2 6.1 0.58
1.00 4.43 1.05 2.77 0.38 1.00 1.05 1.08 6.4 2894.4 1389314.9 6.1 0.58
1.06 4.69 1.11 2.93 0.38 0.89 1.25 1.24 6.8 3051.3 1464608.4 6.1 0.58
1.13 5.00 1.16 3.12 0.37 0.75 1.55 1.45 7.0 3156.0 1514862.7 6.0 0.57
1.19 5.38 1.20 3.36 0.36 0.54 2.21 1.79 7.1 3181.8 1527252.8 5.9 0.54
1.25 6.28 1.23 3.93 0.31 0.00 6.6 2962.1 1421822.7 5.4 0.45
Q =
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)ydoT
THETA
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =18.0 Enter Value
Diameter,do (ft) =1.50
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft
2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.08 0.90 0.03 0.68 0.05 0.65 0.05 0.01 0.1 23.1 11098.9 1.6 0.04
0.15 1.29 0.09 0.97 0.10 0.90 0.10 0.03 0.2 100.5 48254.0 2.4 0.09
0.23 1.59 0.17 1.19 0.14 1.07 0.16 0.07 0.5 234.1 112348.8 3.1 0.15
0.30 1.85 0.25 1.39 0.18 1.20 0.21 0.12 0.9 421.7 202400.0 3.7 0.22
0.38 2.09 0.35 1.57 0.22 1.30 0.27 0.18 1.5 659.6 316600.4 4.3 0.28
0.45 2.32 0.45 1.74 0.26 1.37 0.32 0.25 2.1 943.0 452616.6 4.7 0.34
0.53 2.53 0.55 1.90 0.29 1.43 0.39 0.34 2.8 1266.1 607722.1 5.1 0.41
0.60 2.74 0.66 2.05 0.32 1.47 0.45 0.44 3.6 1622.6 778866.0 5.5 0.47
0.68 2.94 0.77 2.21 0.35 1.49 0.52 0.55 4.5 2005.6 962707.8 5.8 0.52
0.75 3.14 0.88 2.36 0.38 1.50 0.59 0.68 5.4 2407.6 1155629.5 6.1 0.57
0.83 3.34 1.00 2.51 0.40 1.49 0.67 0.81 6.3 2820.3 1353729.7 6.3 0.62
0.90 3.54 1.11 2.66 0.42 1.47 0.75 0.96 7.2 3235.0 1552796.8 6.5 0.66
0.98 3.75 1.22 2.81 0.43 1.43 0.85 1.12 8.1 3642.2 1748255.8 6.7 0.69
1.05 3.96 1.32 2.97 0.44 1.37 0.96 1.30 9.0 4031.4 1935073.1 6.8 0.72
1.13 4.19 1.42 3.14 0.45 1.30 1.09 1.49 9.8 4390.8 2107585.6 6.9 0.74
1.20 4.43 1.52 3.32 0.46 1.20 1.26 1.70 10.5 4706.6 2259179.2 6.9 0.74
1.28 4.69 1.60 3.52 0.45 1.07 1.49 1.96 11.1 4961.7 2381614.8 6.9 0.74
1.35 5.00 1.68 3.75 0.45 0.90 1.86 2.29 11.4 5131.9 2463333.8 6.8 0.72
1.43 5.38 1.73 4.04 0.43 0.65 2.65 2.82 11.5 5173.9 2483481.5 6.6 0.69
1.50 6.28 1.77 4.71 0.38 0.00 10.7 4816.8 2312040.6 6.1 0.57
Q =
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)ydoT
THETA
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =24.0 Enter Value
Diameter,do (ft) =2.00
Units =1.486
n =0.009
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft
2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.0 0.00
0.10 0.90 0.06 0.90 0.07 0.87 0.07 0.02 0.1 49.8 23902.9 1.9 0.06
0.20 1.29 0.16 1.29 0.13 1.20 0.14 0.06 0.5 216.5 103921.1 3.0 0.14
0.30 1.59 0.30 1.59 0.19 1.43 0.21 0.13 1.1 504.1 241957.1 3.8 0.22
0.40 1.85 0.45 1.85 0.24 1.60 0.28 0.24 2.0 908.1 435893.6 4.5 0.32
0.50 2.09 0.61 2.09 0.29 1.73 0.35 0.37 3.2 1420.5 681838.4 5.2 0.41
0.60 2.32 0.79 2.32 0.34 1.83 0.43 0.52 4.5 2030.8 974766.2 5.7 0.51
0.70 2.53 0.98 2.53 0.39 1.91 0.51 0.70 6.1 2726.7 1308805.1 6.2 0.60
0.80 2.74 1.17 2.74 0.43 1.96 0.60 0.91 7.8 3494.6 1677384.9 6.6 0.68
0.90 2.94 1.37 2.94 0.47 1.99 0.69 1.14 9.6 4319.4 2073311.1 7.0 0.77
1.00 3.14 1.57 3.14 0.50 2.00 0.79 1.39 11.6 5185.0 2488792.0 7.4 0.84
1.10 3.34 1.77 3.34 0.53 1.99 0.89 1.67 13.5 6073.8 2915425.3 7.6 0.91
1.20 3.54 1.97 3.54 0.56 1.96 1.00 1.97 15.5 6967.0 3344141.0 7.9 0.97
1.30 3.75 2.16 3.75 0.58 1.91 1.13 2.30 17.5 7843.9 3765086.5 8.1 1.02
1.40 3.96 2.35 3.96 0.59 1.83 1.28 2.66 19.3 8682.1 4167420.8 8.2 1.05
1.50 4.19 2.53 4.19 0.60 1.73 1.46 3.05 21.1 9456.1 4538947.8 8.3 1.08
1.60 4.43 2.69 4.43 0.61 1.60 1.68 3.50 22.6 10136.3 4865423.5 8.4 1.09
1.70 4.69 2.85 4.69 0.61 1.43 1.99 4.02 23.8 10685.6 5129103.8 8.4 1.09
1.80 5.00 2.98 5.00 0.60 1.20 2.48 4.69 24.6 11052.3 5305095.8 8.3 1.06
1.90 5.38 3.08 5.38 0.57 0.87 3.54 5.80 24.8 11142.7 5348486.4 8.1 1.01
2.00 6.28 3.14 6.28 0.50 0.00 23.1 10373.5 4979267.0 7.4 0.84
Q =
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.00 0.50 1.00 1.50 2.00 2.50
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)ydoT
THETA
Allowable Pavement Encroachment
Given:T =9.5 feet (max per city)
W =1.5 feet
Ts =8 feet
Sw =0.0625 ft/ft
Sx =0.03 ft/ft
a =0.59 inches
d =3.24 inches
n =0.013
Sw/Sx =2.08
T/W =6.333333
Capacity for Gutter
equations:
Where:
Qs =Discharge within the Roadway
above the depressed section (cfs)
Qw =Discharge within the depressed
(gutter) section (cfs)
Cf =0.56 for English units
Sx =Pavement cross slope (ft/ft)
Ts =Width of flow in the roadway above
depressed section
So =Gutter longitudinal slope (ft/ft)
Sw =Gutter depression cross slope (ft/ft)
T =Spread (ft)
W =Width of gutter depression (ft)
Capacity solution
Gutter Capacity - Drainage Area A Gutter Capacity - Drainage Area B
So =0.0100
Qs =3.19 cfs
Eo =0.40 cfs
Q =5.35 cfs
Gutter Capacity - Drainage Area C Gutter Capacity - Drainage Area D
So =0.0100
Qs =3.19 cfs
Eo =0.40 cfs
Q =5.35 cfs
Gutter Capacity - Drainage Area E Gutter Capacity - Drainage Area F
So =0.0100
Qs =3.19 cfs
Eo =0.40 cfs
Q =5.35 cfs
Gutter Capacity - Drainage Area G Gutter Capacity - Drainage Area H
So =0.0125 So =0.0050
Qs =3.57 cfs Qs =2.26 cfs
Eo =0.40 cfs Eo =0.40 cfs
Q =5.99 cfs Q =3.79 cfs
Gutter Capacity - Drainage Area I Gutter Capacity - Drainage Area J
So =0.0100 So =0.0140
Qs =3.19 cfs Qs =3.78 cfs
Eo =0.40 cfs Eo =0.40 cfs
Q =5.35 cfs Q =6.34 cfs
Four Points PH 2 Subdivision
Gutter Capacity Calculations
N/A - This flow is directed via existing pipes
into an existing 18" storm drain pipe
N/A - This lot will flow into an
existing 15" storm drain stub
N/A - This lot overland flows into
the existing park pond
SWQQQ
QEQoW
0
S
E1
QQ
2
1
O3
8
S3
5
XfS STSn
CQ
1
8/3
XW
XWo
11T/W
/SS1
/SS1E
Page 1 of 2
Gutter Capacity - Drainage Area K
Summary
DA
Gutter
Capacity (cfs)
25 Yr Design
Flow (cfs)
Capacity
greater than
25- yr flow?
A 5.35 1.19 Yes
B N/A N/A N/A - This runoff overland flows into the existing park pond
C 5.35 1.66 Yes
D N/A N/A N/A - This flow will be directed into an existing 15" storm drain pipe stub
E N/A N/A N/A - This flow is directed via existing pipes into an existing 18" storm drain pipe
F 5.35 2.34 Yes
G 5.99 3.31 Yes
H 3.79 1.95 Yes
I 5.35 3.85 Yes
J 6.34 1.41 Yes
K N/A N/A N/A - This flow will be directed into an existing 18" storm drain pipe stub
Verdict
The gutter capacity is adequate for each drainage area.
N/A - This lot will flow into an existing 18"
storm drain stub
Page 2 of 2
Gutter Section
Given: T =9.0 feet
W =1.50 feet
Ts =7.50 feet
Sw =0.0625 ft/ft
Sx =0.03 ft/ft
a =0.59 inches
d =3.24 inches
n =0.015
Where:
Qs = Discharge within the Roadway
above the depressed section (cfs)
Qw = Discharge within the depressed
(gutter) section (cfs)
Capacity for Inlets on Grade Cf = 0.56 for English units
(Standard 24x36 Curb inlet) Sx = Pavement cross slope (ft/ft)
Ts = Width of flow in the roadway above
Drainage Area A - Existing Curb Inlet depressed section
So = Gutter longitudinal slope (ft/ft)
Qw =2.16 cfs Sw = Gutter depression cross slope (ft/ft)
Qs =3.19 cfs T = Spread (ft)
Cross-sectional area of flow W = Width of gutter depression (ft)
A =1.22 ft2
Gutter Velocity
V =4.41 ft/sec
Fraction of side flow intercepted
Rs =0.15
Total flow capacity intercepted by the inlet
Qint =2.80 cfs
Qbypass =2.56 cfs
Design Q for inlet
Q25 =1.19 cfs Single Inlet Sufficient
Drainage Area C - Existing Curb Inlet
Qw =2.16 cfs
Qs =3.19 cfs
Cross-sectional area of flow
A =1.22 ft2
Gutter Velocity
V =4.41 ft/sec
Fraction of side flow intercepted
Rs =0.15
Total flow capacity intercepted by the inlet
Existing Weir Type Inlet Capacity Calculations
Four Points Phase 2
Page 1 of 2
Qint =2.80 cfs
Qbypass =2.56 cfs
Design Q for inlet
Q25 =1.66 cfs Single Inlet Sufficient
Drainage Area H - Existing Curb Inlet
Qw =0.91 cfs
Qs =2.26 cfs
Cross-sectional area of flow
A =1.22 ft2
Gutter Velocity
V =2.61 ft/sec
Fraction of side flow intercepted
Rs =0.31
Total flow capacity intercepted by the inlet
Qint =1.94 cfs
Qbypass =1.23 cfs
Design Q for inlet
Q25 =1.95 cfs Single Inlet Sufficient
Drainage Area J - Existing Curb Inlet
Qw =2.56 cfs
Qs =3.78 cfs
Cross-sectional area of flow
A =1.22 ft2
Gutter Velocity
V =5.21 ft/sec
Fraction of side flow intercepted
Rs =0.11
Total flow capacity intercepted by the inlet
Qint =3.19 cfs
Qbypass =3.15 cfs
Design Q for inlet
Q25 =1.41 cfs Single Inlet Sufficient
Page 2 of 2
Basins F & G
East Jordan Iron Works Orifice Flow Calculations: From Manufacturer's Website
Where: Q = Flow (cfs)
A = Open area in grate (in^2)
d = Depth of water over grate (in)
C = Rating Coefficient
C = 0.0108 *From Manufacturer
A = 225 in^2 *From Shop Drawing Submittal
d = 4 in *City Maximum
Q =4.86 cfs
Basin Flows
Half of Basin F 1.17 *Half is appropriate as Basin F flows into two sag inlets
Half of Basin F plus Basin G 4.48 *Half of Basin F and all of Basin G will flow into one sag inlet
Four Points Phase 2
Existing Orifice Type (Sag) Curb Inlet Capacity Calculations
𝑄=𝐶∗𝐴∗√𝑑
Appendix D:
Detention Facility Calculations
Four Points Phase 2
Existing Park Detention Pond
Calculation of Required Volume for Storm Detention Pond
(Reference: Bozeman Stormwater Master Plan - 1982)
Design Rainfall Freq.10 year (see page III - 5 of master plan)
IDF coefficient a 0.64
IDF coefficient b 0.00
IDF coefficient n 0.65
Pre-development Calculations Post-development Calculations
Area (AC)C Area (AC)C
Areas (ft2):Basin 1 9.49 0.20 Areas (AC):Basin A 1.26 0.67
Basin B 5.36 0.20
Basin C 1.25 0.74
Basin D 1.62 0.65
Total:9.49 Total:9.49
total area:9.49 acres total area:9.49 acres
composite C:0.20 composite C:0.41
Overland tc Overland tc
average slope:1.00 percent average slope:1.5 percent
travel distance:900 feet travel distance:900 feet
tc:50 minutes tc:34 minutes
Channel tc Channel tc
channel tc:minutes channel tc:2.6 minutes
Total tc:50 minutes Total tc:36 minutes
intensity at tc (fig 23):0.72 in/hr intensity at tc (fig 23):0.89 in/hr
pre-devel peak runoff:1.36 cfs post-devel peak runoff:3.45 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
24 1.16 4.52 6511 1957 4554
25 1.13 4.40 6604 2038 4566
26 1.10 4.29 6696 2120 4576
27 1.08 4.19 6785 2201 4583
28 1.05 4.09 6872 2283 4589
29 1.03 4.00 6956 2365 4592
30 1.00 3.91 7039 2446 4593
32 0.96 3.75 7200 2609 4591
34 0.93 3.61 7355 2772 4583
36 0.89 3.47 7503 2935 4568
38 0.86 3.35 7647 3098 4548
40 0.83 3.24 7785 3261 4524
42 0.81 3.14 7919 3424 4495
44 0.78 3.05 8049 3588 4462
46 0.76 2.96 8175 3751 4425
48 0.74 2.88 8298 3914 4385
50 0.72 2.81 8418 4077 4341
52 0.70 2.74 8534 4240 4294
54 0.69 2.67 8647 4403 4245
56 0.67 2.61 8758 4566 4192
58 0.65 2.55 8866 4729 4137
60 0.64 2.49 8972 4892 4080
required detention storage (ft3) =4,593
Detention Pond Calculations:
design depth of pond 1.50 feet
max side slope 4.00 horizontal to 1.00 vertical
length/width ratio 3.00
min. particle removed 40 microns (1 micron = 1 x 10-6 meters)
settling velocity of particle 0.0069 feet/second
min. pond to settle particle 499 square feet
Existing approximate pond dimensions
width 46
length 100
Volume held between contours:
Cumulative
Contour Area (ft2)Delta V (ft3)Volume (ft3)
4688.21 3,834 0 0
4689.00 4,681 3,363 3,363
4689.71 5,509 3,617 6,981
Design storage at 1.5' depth (ft3) =6,981
0.5 inch stormwater in roadways calculations within Basins A & C
C
Areas (ft2):asphalt 59,271 0.90
A =1.36 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.03 cfs
Volume = 2,204 cf
*0.5 inch stormwater from asphalt areas in Basins D
C
**Areas (ft2):asphalt 10,585 0.90 * Assumes 15% of the developed lot will be asphalt
A =0.24 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.005 cfs
Volume = 394 cf
Total Volume=2,598 cf
Elevated Weir Elevation above pond bottom
Use Interpolation to solve for the pond height at the required volume
0.5" storm Volume 2,598 cf
Volume of Pond at 0'=0 cf
Volume of Pond at 0.79'=3,363 cf
Interpolated Depth=0.61 ft
slot weir h =0.61 ft
overflow weir h =1.50 ft
proposed slot elev =4688.82 ft
prop. overflow weir elev =4689.71 ft
existing slot elev = 4687.36 ft *the slot is lower than the pond bottom because there is a pipe from pond to outfall structure
existing overflow elev =4689.71 ft
existing slot width =0.25 ft
proposed slot width =0.49 ft
Flow Structure Calculations - Park Pond
(Reference: City of Bozeman, Design Standards and Specifications Policy, March 2004, II.D.2, page 24)
Note: see Figure A-2 in above reference.
Rectangular weir - Q=3.33LH3/2
Determine Outlet Slot Width needed:
Pre-development flow rate = 1.36 cfs
Vertical Slot Height = 10.68 inches
Req'd Outlet Slot Width = 0.49 feet or 5 7/8 inches
Determine Outlet Flow:
Outlet Slot Width = 5.83 inches
stage above weir (ft)stage above bottom (ft)Q (cfs)Q (gpm)
0.00 0.61 0.00 0
0.10 0.71 0.05 23
0.20 0.81 0.14 65
0.30 0.91 0.27 119
0.40 1.01 0.41 184
0.50 1.11 0.57 257
0.60 1.21 0.75 338
0.70 1.31 0.95 426
0.80 1.41 1.16 520
0.89 1.50 1.36 610
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.00 0.50 1.00 1.50Discharge (cfs)Stage (ft)
Flow through outlet
Stage vs. Discharge
Four Points Phase 2
Existing Blondie St Detention Pond
Calculation of Required Volume for Storm Detention Pond
(Reference: Bozeman Stormwater Master Plan - 1982)
Design Rainfall Freq.10 year (see page III - 5 of master plan)
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Pre-development Calculations Post-development Calculations
Area (AC)C Area (AC)C
Areas (ft2):Basin E, F & G 10.12 0.20 Areas (AC):Basin E 5.52 0.65
Basin F 1.92 0.74
Basin G 2.68 0.65
Total:10.12 Total:10.12
total area:10.12 acres total area:10.12 acres
composite C:0.20 composite C:0.67
Overland tc Overland tcaverage slope:1.38 percent average slope:2.0 percent
travel distance:800 feet travel distance:800 feet
tc:43 minutes tc:18 minutes
Channel tc Channel tc
channel tc:minutes channel tc:2.6 minutes
Total tc:43 minutes Total tc:21 minutes
intensity at tc (fig 23):0.80 in/hr intensity at tc (fig 23):1.27 in/hr
pre-devel peak runoff:1.61 cfs post-devel peak runoff:8.60 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
30 1.00 6.78 12203 2904 9300
32 0.96 6.50 12482 3097 9385
34 0.93 6.25 12750 3291 9459
36 0.89 6.02 13007 3485 9523
38 0.86 5.81 13256 3678 9578
40 0.83 5.62 13496 3872 9624
42 0.81 5.45 13728 4065 9663
44 0.78 5.29 13954 4259 9695
46 0.76 5.14 14173 4452 9720
48 0.74 4.99 14385 4646 9739
50 0.72 4.86 14592 4840 9753
52 0.70 4.74 14794 5033 9761
54 0.69 4.63 14991 5227 9764
56 0.67 4.52 15183 5420 9762
58 0.65 4.42 15370 5614 9756
60 0.64 4.32 15554 5808 9746
62 0.63 4.23 15733 6001 9732
required detention storage (ft3) =9,764
Detention Pond Calculations:
design depth of pond 2.00 feet
max side slope 4.00 horizontal to 1.00 vertical
length/width ratio 3.00
min. particle removed 40 microns (1 micron = 1 x 10-6 meters)
settling velocity of particle 0.0069 feet/second
min. pond to settle particle 1246 square feet
existingpond dimentions assuming vertical side slopes
width 35
length 148
Volume held between contours:
Cumulative
Contour Area (ft2)Delta V (ft3)Volume (ft3)
4691.00 757
4691.50 3,412 1,042 1,042
4692.00 5,974 2,347 3,389
4692.50 6,714 3,172 6,561
4693.00 8,101 3,704 10,265
Design storage at 2' depth (ft3) =10,265
0.5 inch stormwater in roadways calculations within Basin F
C
Areas (ft2):asphalt 39,262 0.90
A =0.90 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.02 cfs
Volume = 1,460 cf
*0.5 inch stormwater from asphalt area in Basin E & G
C
*Areas (ft2):asphalt 53,579 0.90 *Assumes 15% of the lot will be asphalt.
A =1.23 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.023 cfs
Volume = 1,993 cf
Total Volume=3,453 cf
Elevated Weir Elevation above pond bottom
Use Interpolation to solve for the pond height at the required volume
0.5" storm Volume 3,453 cf
Volume of Pond at 1.0'=3,389 cf
Volume of Pond at 1.5'=6,561 cf
Interpolated Depth=1.01 ft
slot weir h =1.01 ft
overflow weir h =2.00 ft
proposed slot elev =4692.01 ft
prop. overflow weir elev =4693.00 ft
existing slot elev =4690.84 ft
existing overflow elev =4692.35 ft
existing slot width =0.33 ft
proposed slot width =0.49 ft
Flow Structure Calculations - Blondie St Pond
(Reference: City of Bozeman, Design Standards and Specifications Policy, March 2004, II.D.2, page 24)
Note: see Figure A-2 in above reference.
Rectangular weir - Q=3.33LH3/2
Determine Outlet Slot Width needed:
Pre-development flow rate = 1.61 cfs
Vertical Slot Height = 11.88 inches
Req'd Outlet Slot Width = 0.49 feet or 5 7/8 inches
Determine Outlet Flow:
Outlet Slot Width = 5.90 inches
stage above weir (ft)stage above bottom (ft)Q (cfs)Q (gpm)
0.00 1.01 0.00 0
0.10 1.11 0.05 23
0.20 1.21 0.15 66
0.30 1.31 0.27 121
0.40 1.41 0.41 186
0.50 1.51 0.58 260
0.60 1.61 0.76 342
0.70 1.71 0.96 431
0.80 1.81 1.17 526
0.90 1.91 1.40 628
0.99 2.00 1.61 724
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.00 0.50 1.00 1.50Discharge (cfs)Stage (ft)
Flow through outlet
Stage vs. Discharge
Four Points Phase 2
Existing Cattail St Detention Pond
Calculation of Required Volume for Storm Detention Pond
(Reference: Bozeman Stormwater Master Plan - 1982)
Design Rainfall Freq.10 year (see page III - 5 of master plan)
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Pre-development Calculations Post-development Calculations
Area (AC)C Area (AC)C
Areas (ft2):Basin 1 13.23 0.20 Areas (AC):Basin H 2.40 0.67
Basin I 3.05 0.65
Basin J 0.95 0.74
Basin K 6.83 0.65
Total:13.23 Total:13.23
total area:13.23 acres total area:13.23 acres
composite C:0.20 composite C:0.66
Overland tc Overland tc
average slope:1.07 percent average slope:1.2 percent
travel distance:1400 feet travel distance:1198 feet
tc:62 minutes tc:27 minutes
Channel tc Channel tc
channel tc:minutes channel tc:2.6 minutes
Total tc:62 minutes Total tc:29 minutes
intensity at tc (fig 23):0.63 in/hr intensity at tc (fig 23):1.02 in/hr
pre-devel peak runoff:1.67 cfs post-devel peak runoff:8.89 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
30 1.00 8.77 15786 2998 12788
32 0.96 8.41 16147 3198 12949
34 0.93 8.09 16493 3398 13095
36 0.89 7.79 16827 3598 13229
38 0.86 7.52 17148 3798 13350
40 0.83 7.27 17459 3998 13461
42 0.81 7.05 17759 4198 13562
44 0.78 6.84 18051 4398 13653
46 0.76 6.64 18334 4598 13737
48 0.74 6.46 18609 4797 13812
50 0.72 6.29 18877 4997 13880
52 0.70 6.13 19138 5197 13941
54 0.69 5.99 19392 5397 13995
56 0.67 5.85 19641 5597 14044
58 0.65 5.71 19883 5797 14087
60 0.64 5.59 20121 5997 14124
62 0.63 5.47 20353 6197 14156
64 0.61 5.36 20581 6397 14184
66 0.60 5.25 20803 6596 14207
68 0.59 5.15 21022 6796 14226
70 0.58 5.06 21236 6996 14240
72 0.57 4.96 21447 7196 14251
74 0.56 4.88 21653 7396 14257
76 0.55 4.79 21856 7596 14260
78 0.54 4.71 22056 7796 14260
80 0.53 4.64 22252 7996 14257
82 0.52 4.56 22445 8196 14250
84 0.51 4.49 22636 8395 14240
required detention storage (ft3) =14,260
Detention Pond Calculations:
design depth of pond 1.50 feet
max side slope 4.00 horizontal to 1.00 vertical
length/width ratio 3.00
min. particle removed 40 microns (1 micron = 1 x 10-6 meters)
settling velocity of particle 0.0069 feet/second
min. pond to settle particle 1288 square feet
Existing approximate pond dimensions
width 55
length 270
Volume held between contours:
Cumulative
Contour Area (ft2)Delta V (ft3)Volume (ft3)
4686.62 11,054
4687.00 11,941 4,369 4,369
4688.00 14,478 13,210 17,579
4688.10 14,737 1,461 19,039
Design storage at 1.5' depth (ft3) =19,039
0.5 inch stormwater in roadways calculations within Basins H & J
C
Areas (ft2):asphalt 69,779 0.90
A =1.60 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.03 cfs
Volume = 2,595 cf
*0.5 inch stormwater from asphalt areas in Basins I & K
C
**Areas (ft2):asphalt 64,556 0.90 * Assumes 15% of the developed lot will be asphalt
A =1.48 acres
I = 0.021 in/hr (0.5" in 24 hrs)
C =0.90
Q = 0.028 cfs
Volume = 2,401 cf
Total Volume=4,996 cf
Elevated Weir Elevation above pond bottom
Use Interpolation to solve for the pond height at the required volume
0.5" storm Volume 4,996 cf
Volume of Pond at 0.38'=4,369 cf
Volume of Pond at 1.38'=17,579 cf
Interpolated Depth=0.53 ft
slot weir h =0.53 ft
overflow weir h =1.50 ft
proposed slot elev =4687.15 ft
prop. overflow weir elev =4688.10 ft
existing slot elev =4686.1 ft *the slot is lower than the pond bottom because there is a pipe from pond to outfall structure
existing overflow elev =4689.93 ft
existing slot width =0.25 ft
proposed slot width =0.54 ft
Flow Structure Calculations - Cattail St Pond
(Reference: City of Bozeman, Design Standards and Specifications Policy, March 2004, II.D.2, page 24)
Note: see Figure A-2 in above reference.
Rectangular weir - Q=3.33LH3/2
Determine Outlet Slot Width needed:
Pre-development flow rate = 1.67 cfs
Vertical Slot Height = 11.43 inches
Req'd Outlet Slot Width = 0.54 feet or 6 4/8 inches
Determine Outlet Flow:
Outlet Slot Width = 6.46 inches
stage above weir (ft)stage above bottom (ft)Q (cfs)Q (gpm)
0.00 0.53 0.00 0
0.10 0.63 0.06 25
0.20 0.73 0.16 72
0.30 0.83 0.29 132
0.40 0.93 0.45 203
0.50 1.03 0.63 284
0.60 1.13 0.83 374
0.70 1.23 1.05 471
0.80 1.33 1.28 575
0.90 1.43 1.53 687
0.97 1.50 1.71 768
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.00 0.50 1.00 1.50Discharge (cfs)Stage (ft)
Flow through outlet
Stage vs. Discharge
Appendix E:
Stormwater Maintenance Plan
Four Points Phase 2
Storm Water Maintenance Plan
The stormwater facilities will be maintained and operated by the Owner of the development.
The storm water facilities are intended to be operated with minimal maintenance. The suggested
minimum maintenance, which will prevent system failure and reduce repair fees, are described
below:
1. Site Housekeeping – regularly inspect all stormwater infrastructure and keep them free of
leaves, rocks, trash, and other debris.
2. Monitoring – inspect the facilities periodically, especially after heavy rains (preferably
monthly and after each storm event that delivers 0.5 inches or more of rainfall), to observe
system performance. Significant ponding can be a warning sign of a plugged pipe or inlet.
3. Quarterly Maintenance - re-sod damaged or maintained landscaped areas. Inspect the flow
control outfall structures to ensure that they are functioning properly and are free of debris.
If needed, clean accumulated soil in stormwater pipes, culverts, or inlets.
4. Annual Maintenance - Remove accumulated sediment in sumps during the summer months.
If accumulated sediment covers vegetation within the pond, remove it. Perform weed
control within the pond and landscaped areas annually.
5. Owner to maintain and fund Operation and Maintenance of stormwater facilities.
_______________________________
Steve Moore, Four Points MT LLC