HomeMy WebLinkAbout009 Stormwater Report
STORMWATER MANAGEMENT
DESIGN REPORT
FOR:
Buffalo Restoration
555 Manley Rd,
Bozeman, MT
Prepared By:
WWC/Madison Engineering
895 Technology Drive, Suite 203
Bozeman, MT 59718
(406) 586-0262
August 2024
Page 1 of 3
895 Technology Boulevard, Suite 203, Bozeman, MT 59718 | 406.586.0262
Buffalo Restoration
555 Manley Rd,
Stormwater Design Report
Introduction
This design report will give an overview of the proposed stormwater system for the proposed site
improvements of Buffalo Restoration located at 555 Manley Rd. There is a proposed addition to
the existing site including another building and additional parking. The property is located at
Gallatin Park Sub, S36, T01, RO5E, Block 2, Lot 2-A.
The proposed addition is a building that will accommodate increased services by Buffalo
Restoration and will be constructed in a single phase on M-1 (light manufacturing) zoned
property. The single building will be constructed with associated on-site parking and
landscaping. Open space is not required for the site.
The stormwater system will include utilizing proposed curb chases, a square cast iron area drain,
a curb inlet, storm piping and an on-site detention pond. Water will be conveyed by a
combination of sheet flow, curb and gutter and piping that will direct stormwater to an on-site
detention/infiltration pond on the east end of the site and an area drain on the west side of the
site. The proposed pond has been sized accordingly, and the area drain will be excavated to
native gravels to permit maximum infiltration.
The following references were used in the preparation of this report:
a. City of Bozeman Modifications to Montana Public Works Standard Specifications.
Seventh edition, addendum No 3.
b. City of Bozeman Design Standards and Specifications Policy, March 2004. Addendum
#7
c. Circular DEQ 8, Montana Standards for Subdivision Storm Drainage, 2002 Edition
Runoff and Basin Calculation
A 25-year, 2-hour design rainfall frequency was used for calculating the storm sewer inlet and
piping facilities per City of Bozeman Design Standards. A 10-year, 2-hour storm intensity was
used for calculating the basin sizing utilizing the rational method in accordance with the COB
Design Standards. A runoff coefficient C of 0.90 was used for impervious areas and a C value of
0.20 was used for landscaped areas. The tables below illustrate the calculated runoff coefficients
and areas for each as well as a summary of the stormwater basin calculations.
Page 2 of 3
Table 1: Stormwater Basin Run-Off Calculations
Basin Weighted C Total Area
(sf)
Impervious
Area (sf)
Landscaped
Area (sf)
A 0.75 33,249 16,501 16,748
B 0.90 3,930 3,930 0
Table 2: Stormwater Basin Calculations
Basin Required Storage (cf) Provided Storage (cf)
A 1,245 2,000
B 240 290
Basin B discharges to a low point on the northwest side of the site. This small area drains to a
square cast iron dry well area drain. The area drain is to be excavated down to native soils and
over excavated to place clean washed rock below and around structure to ensure proper drainage.
The washed rock is to be set a minimum of 9” in existing gravels.
Conveyance Capacity
The proposed private stormwater collection and detention/infiltration system was designed to
convey the 25-year storm event per COB Design Standards. The conveyance structures for Basin
A include a curb inlet and piping that directs stormwater run-off to the on-site
Page 3 of 3
detention/infiltration basins. A twelve-inch storm sewer pipe is proposed to collect and convey
the stormwater run-off to a detention/infiltration basin. Stormwater piping calculations, which
are included in Appendix B, indicate that the pipe can convey a maximum of 2.7 cubic feet per
second. The conveyance structures for Basin B include a 24” dry well area drain excavated down
to native gravels and backfilled with clean washed rock to ensure proper drainage. Appendix C
includes 25-year event storm runoff calculations and identifies the anticipated peak runoff
flowrate to be 0.83 cubic feet per second for Basin A and 0.40 cubic feet per second for Basin B.
Curb and Curb Inlet calculations are included in Appendix F of this report.
Stormwater Detention/Infiltration Basin
All the stormwater runoff from the site is proposed to be conveyed to on-site
detention/infiltration basins and ultimately infiltrate into native gravels. The detention storage
volumes were sized based on the 10-year, 2-hour design rainfall frequency per the COB Design
Standards. The rational method was used to determine post-development stormwater flows. The
calculations for all stormwater storage facilities are included in Appendix D of this report. The
proposed stormwater facilities reduce the post-development runoff rate to zero. All impervious
surface runoff is conveyed to the infiltration systems and then infiltrates into the ground.
Stormwater Facility Maintenance
The proposed storm drainage facilities will be privately operated and maintained by the property
owner of the on-site development. Included in this report is Appendix E, a stormwater
maintenance plan.
Conclusion
The proposed stormwater drainage facilities for Buffalo Restoration site improvements have
adequate capacity to accommodate the 25-year storm event per City of Bozeman design
standards. The proposed detention facilities have adequate capacity to accommodate the 10-year,
2-hour event per City of Bozeman standards. Based on the calculations provided in the appendix,
the proposed system has adequate capacity to handle the stormwater. The existing system is not
being affected or being distributed any additional runoff, therefore calculations for the existing
system are not required.
Appendices
A. Grading/Drainage Plan
B. Storm Piping Calculations
C. Stormwater Runoff Calculations
D. Detention Pond Sizing Calculations
E. Stormwater Maintenance Plan
F. Curb and Gutter Capacity
APPENDICES
Appendix A – Grading/Drainage Plan &
Detail Sheet
F
F
F
DFOFO
FOFOFOFO
UGPUGPUGP
XX FONGNGNGFOFOSTSS
SS
SS
SSSS O
OOF
F
P
E
P
E
ST
FF = 4698.63 (APPROX)-1.18%
-1
.
7
4%
TBC 4697.45
BEGIN LAYDOWN
TBC 4697.74
BEGIN LAYDOWN
TBC 4698.32
TBC 4698.50
GRADE BREAK
TBC 4699.61
TBC 4698.49
TBC 4699.52
TBC 4699.54
TBC 4699.60
TBC 4699.78
18" WIDE
CURB CHASE
S = -0.50%
12" PVC
UNDERGROUND
STORM PIPE
L=77 LF, S=0.5%
CURB
INLET
12" PVC STORM PIPE
INV 4695.21
SQUARE CAST IRON
DRY WELL AREA
DRAIN. EXCAVATE
TO NATIVE SOILS.
INSTALL CLEAN
WASHED ROCK
AROUND AND BELOW
STRUCTURE
11'x11'x6'.
12" PVC STORM PIPE
INV 4694.82
GRADE BREAK
TBC 4698.43
EXISTING
SWALE TO REMAIN
4'x4' GRAVEL
INFILTRATOR
EXCAVATE TO NATIVE
SOILS AND BACKFILL
WITH WASHED ROCK
STORM WATER
POND 3:1 SIDE
SLOPES
AREA = 2,000 CF
46
9
8
.
5
0
4699.
0
0
4698.00
4698.00
GRADE BREAK 469
8
.
0
0
469
7
.
5
0
FG 4697.90
469
9
TEL
GAS
OHP
UP
LEGEND
ST
DESIGNED BY:
DRAWN BY:
CHECKED BY:
DATE:
PCR
PCR
EWR
7/25/2024
SHEET
7NO.DATEREVISIONPREPARED BYBYGRADING & DRAINAGE PLANFORMESCENT ARCHITECTSBOZEMAN, MTBUFFALO RESTORATIONENGINEERINGPROJECT NO. 2023507 895 TECHNOLOGY BLVD., SUITE 203BOZEMAN, MT 59718(406) 624-3910www.wwcengineering.com0
SCALE: 1" = 30'
30'15'1.REVISED PER CITY REVIEWPCR10/21/24
*SEE O.S.H.A. CONSTRUCTION STANDARDS FOR EXCAVATION
TYPE II PIPE BEDDING
WHERE REQUIRED FOR
SOFT OR UNSTABLE
FOUNDATION
TYPE I PIPE BEDDING
EXISTING
STREET
SURFACE
SPECIFIED BACKFILL MATERIAL
COMPACTED AS SPECIFIED IN
SECTION 02201
TRENCH WIDTH=O.D.
OF PIPE PLUS 2'
MIN. TRENCH WIDTH=3.5'
4"
6"
TYPE "A"
OR "B"
TRENCH
BACKFILL
INSTALL DETECTABLE WARNING
TAPE 18" MIN. 24" MAX DEPTH.
PAVEMENT SECTION PLACED
AND COMPACTED PER CITY
OF BELGRADE STDS.
GROUND
SURFACE OR
SUBGRADE
NOTE: WHERE TRENCH PASSES THROUGH EXISTING PAVEMENT THE
PAVEMENT SHALL BE CUT ALONG A NEAT VERTICAL LINE A MINIMUM OF 12"
FROM THE EDGE OF THE TRENCH OPENING. WHERE NEAT LINE IS LESS THAN
3" FROM EDGE OF EXISTING PAVEMENT OR CURB AND GUTTER SECTION.
REMOVE AND REPLACE ENTIRE PAVEMENT SECTION BETWEEN TRENCH AND
EDGE OF PAVEMENT.
VERTICAL TRENCH WALLS
WITH SHORING TO CONFORM
TO O.S.H.A. REGULATIONS*
TYPE 2 EXC.
BACKSLOPE AS
SPECIFIED TO
CONFORM TO O.S.H.A.
REGULATIONS*
TYPE 1 EXC.
#10 AWG INSULATED
TRACER WIRE
NOTES:
TOPSOIL
(TYP.)
CRUSHED
GRAVEL BASE -
3" MIN.
SUB BASE
COURSE AS
REQUIRED
CATCH CURB
SPILL CURB
DEPRESS CURB TO THIS
LINE FOR CURB DROP.
COMPACTED SUBGRADE
1. SUBGRADE AND SUB BASE COURSE COMPACTION SHALL CONFORM TO
SECTION 02230 (MPWSS)
2. CONTRACTION JOINTS SHALL BE PLACED AT 10' INTERVALS AND SHALL HAVE A
MINIMUM DEPTH OF 3/4" AND MINIMUM WIDTH OF 1/8".
3. 1/2" EXPANSION JOINT MATERIAL SHALL BE PLACED AT ALL P.C.S, P.T.S, CURB
RETURNS AND AT NOT MORE THAN 300' INTERVALS. THE EXPANSION MATERIAL
SHALL EXTEND THROUGH THE FULL DEPTH OF THE CURB AND GUTTER.
4. NO CURB AND GUTTER SHALL BE PLACED WITHOUT A FINAL FORM INSPECTION
BY CITY ENGINEER OR HIS REPRESENTATIVE.
5. CONCRETE SHALL BE CLASS M-4000.
6. CRUSHED GRAVEL BASE SHALL MEET THE REQUIREMENTS OF SECTION 02235
(MPWSS).
6
9 INTEGRAL CONCRETE CURB AND GUTTER
4
9 TYPICAL TRENCH DETAIL
24" DIA
6'
VARIES
5
9 24-INCH I.D.DRY WELL AREA DRAIN
18"
5"
9"
DESIGNED BY:
DRAWN BY:
CHECKED BY:
DATE:
PCR
PCR
EWR
7/25/2024
SHEET
9NO.DATEREVISIONPREPARED BYBYDETAILSFORMESCENT ARCHITECTSBOZEMAN, MTBUFFALO RESTORATIONENGINEERINGPROJECT NO. 2023507 895 TECHNOLOGY BLVD., SUITE 203BOZEMAN, MT 59718(406) 624-3910www.wwcengineering.com
Appendix B – Storm Piping Calculations
12" PVC Appendix B
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =12 Enter Value
Diameter,do (ft) =1
Units =1.486
n =0.013
Slope, S (ft/ft)0.005
Depth, y (ft)Theta (rad)
Area, A
(ft2)
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
0.05 0.90 0.01 0.45 0.03 0.44 0.03 0.00 0.0 5.4 2606.2 0.8 0.01
0.10 1.29 0.04 0.64 0.06 0.60 0.07 0.01 0.1 23.6 11330.7 1.3 0.03
0.15 1.59 0.07 0.80 0.09 0.71 0.10 0.02 0.1 55.0 26381.0 1.7 0.04
0.20 1.85 0.11 0.93 0.12 0.80 0.14 0.04 0.2 99.0 47526.2 2.0 0.06
0.25 2.09 0.15 1.05 0.15 0.87 0.18 0.06 0.3 154.9 74342.0 2.2 0.08
0.30 2.32 0.20 1.16 0.17 0.92 0.22 0.09 0.5 221.4 106280.3 2.5 0.10
0.35 2.53 0.24 1.27 0.19 0.95 0.26 0.12 0.7 297.3 142701.2 2.7 0.11
0.40 2.74 0.29 1.37 0.21 0.98 0.30 0.16 0.8 381.0 182888.0 2.9 0.13
0.45 2.94 0.34 1.47 0.23 0.99 0.34 0.20 1.0 471.0 226056.5 3.1 0.15
0.50 3.14 0.39 1.57 0.25 1.00 0.39 0.25 1.3 565.3 271357.0 3.2 0.16
0.55 3.34 0.44 1.67 0.26 0.99 0.44 0.30 1.5 662.2 317873.6 3.3 0.17
0.60 3.54 0.49 1.77 0.28 0.98 0.50 0.35 1.7 759.6 364617.1 3.4 0.18
0.65 3.75 0.54 1.88 0.29 0.95 0.57 0.41 1.9 855.2 410513.5 3.5 0.19
0.70 3.96 0.59 1.98 0.30 0.92 0.64 0.47 2.1 946.6 454380.7 3.6 0.20
0.75 4.19 0.63 2.09 0.30 0.87 0.73 0.54 2.3 1031.0 494888.9 3.6 0.21
0.80 4.43 0.67 2.21 0.30 0.80 0.84 0.62 2.5 1105.2 530485.1 3.7 0.21
0.85 4.69 0.71 2.35 0.30 0.71 1.00 0.71 2.6 1165.1 559234.5 3.6 0.21
0.90 5.00 0.74 2.50 0.30 0.60 1.24 0.83 2.7 1205.0 578423.2 3.6 0.20
0.95 5.38 0.77 2.69 0.29 0.44 1.77 1.02 2.7 1214.9 583154.2 3.5 0.19
1.00 6.28 0.79 3.14 0.25 0.00 2.5 1131.0 542897.6 3.2 0.16
Q =
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.00 0.20 0.40 0.60 0.80 1.00 1.20
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)ydoT
THETA
Appendix C – Stormwater Runoff
Calculations
Buffalo Restoration
25 year Storm Event
Stormwater Run-off Calculation
Design Rainfall Freq.25 year
IDF coefficient a 0.78
IDF coefficient b
IDF coefficient n 0.64
Stormwater Drain to Pond
Basin A Post-Development Calculations
C
Areas (ft2):Landscape 16,748 0.20
Impervious 16,501 0.90
Total:33,249 0.55
total area:0.763 acres
composite C:0.55
Overland tc
average slope:1.1 percent
travel distance:181 feet
tc:13 minutes
Total tc:13 minutes
intensity at tc (fig 23):2.03 in/hr
Peak runoff:0.85 cfs
Pipes Max Flow:2.7 cfs
Storm Runoff Calculation - 25 Year Event.xls
Appendix D – Detention Pond Sizing
Calculations
Buffalo Restoration
Stormwater Detention/Infiltration Calculations
Basin A + B
Calculation of Required Volume for Storm Water Retention & Infitration System
Design Rainfall Freq.10 10 Year - 2 Hour event
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations:
Basin A
Total Basin Area:33,249 sf
C
Areas (ft2):Roof Area 0.90
Impervious 16,748 0.90
Landscaped 16,501 0.20
Total:33,249 0.55
Retention Basin Calculation:
Q = CIA
C =0.55 (post-development)
I = 0.41 in/hr (10-yr, 2-hr storm)
A = 0.76 acres
Qpost =0.17 cfs
Required retention storage (ft3) =1,245 ft3 (10-yr, 2-hr storm)
Provided retention storage (ft3) =2,000 ft3
Post-development Calculations:
Basin B
Total Basin Area:3,930 sf
C
Areas (ft2):Impervious 3,930 0.90
Landscaped
Total:3,930 0.90
Retention Basin Calculation:
Q = CIA
C =0.90 (post-development)
I = 0.41 in/hr (10-yr, 2-hr storm)
A = 0.09 acres
Qpost =0.03 cfs
Required retention storage (ft3) =240 ft3 (10-yr, 2-hr storm)
Provided retention storage (ft3) =290 ft3
Appendix E – Stormwater Maintenance
Plan
K:\Bozeman\Formescent Architects\2024261 Buffalo Restoration Site Plan\08Reports\Storm
STORMWATER MAINTENANCE PLAN
Buffalo Restoration
Owner’s responsibility for routine inspection and maintenance
1. Keep the outlet and inlets of the facility free of leaves, rocks, and other debris.
2. The storm water detention facilities are to be mowed regularly. During the
summer, approximately once every two weeks, the grass is to be mowed and the cuttings
are to be promptly removed and disposed of. Unless visibly tainted, dispose of lawn
clippings in the same manner as yard waste. Otherwise, bag and take to a sanitary
landfill.
3. Remove sediment by hand with a flat bottom shovel during the summer months
whenever sediment covers vegetation. Have the grass cut short in that particular location
so that the bed can be made as level as possible.
5. Re-sod damaged or maintained areas immediately, or use grass plugs from the
adjacent up-slope area.
6. Inspect the facilities periodically, especially after heavy rains (preferably monthly
and after each storm that delivers .5 inches of rainfall).
7. Inspect flow control outlet semi-annually. Clean outlet when soil and vegetation
buildup interfere with flow introduction.
9. See that litter and other debris are removed in order to reduce the tendency to
channel when trash accumulates.
10. Owner to maintain and fund Operation and Maintenance of stormwater detention
facility.
_______________________________
Owner
Appendix F –
Curb and Gutter Capacity
Appendix F
Pavement Encroachment
Given:T =10 feet
W =1.5 feet
Ts =8.5 feet
Sw =0.083 ft/ft
Sx =0.02 ft/ft
a =1.14 inches
d =2.4 inches
n =0.015 Manning's Coeff.
Sw/Sx =4.15
T/W =6.666667
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/ft)
W =Width of gutter depression (ft/ft)
Q = Calculated flow for half-street (cfs)
Eo =Qw/Q, the ratio of gutter flow, Qw, to total flow, Q
Capacity solution
So =0.018 Summary
Qs =2.19 cfs
Eo =0.45 cfs
Q=3.95 cfs
Q25 =0.85 cfs
Buffalo Restoration
Gutter Capacity Calculations
With a roadway encroachment of 10 feet,
the maximum capacity of all gutters
exceeds the 25-year storm event design
flow.
Buffalo Restoration - Curb Inlet
Q > Q25 3.95 > 0.85
SWQQQ+=
QEQoW=
0
S
E1
QQ−=
2
1
O3
8
S3
5
X
f
S STSn
CQ=
()
1
8/3
XW
XWo
11T/W
/SS1
/SS1E
−
−
−+
+=
Buffalo Restoration
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