HomeMy WebLinkAbout06 - Design Report - Fellowship Baptist Church - N 27th Improvements SEP 2 8 20006
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Stormwater Investigation
For
Fellowship Baptist Church
North 27th Avenue Improvements
Prepared For:
Fellowship Baptist Church
Bozeman, MT 59715
Prepared By:
HKM Engineering Inc.
601 Nikles Dr., Ste. 2
Bozeman, MT 59715
September 22, 2006
04C364.102
North 271h Avenue—Stormwater Investigation August, 2006
Table of Contents
Page
Purpose ...........................................................................................................................................3
ProjectOverview............................................................................................................................3
Preliminary Conditions Summary...................................................................................................3
Basisof Calculations.......................................................................................................................3
StormwaterRetention.....................................................................................................................3
Stormwater Treatment and Release................................................................................................6
ConveyanceFacilities.....................................................................................................................6
Maintenance.................................................................................................................................... 7
A. Inspection Program..............................................................................................................7
B. Maintenance Program ..........................................................................................................7
Conclusion ..................................................................................................................................... 7
Tables
Table I -North 27th Avenue Storage Stormwater Quantities.........................................................4
Table 2 -North 271h Avenue Conveyance Capacity.......................................................................7
Figures
Figure I - Storm Water Plan- Layout............................................................................................5
Appendices
Appendix A - Peak Runoff Rate and Detention Pond Volume Calculations
Appendix B -Conveyance Facility Calculations
Page 2 of 7
North 27th Avenue—Stormwater Investigation August, 2006
Purpose
This engineer's report is intended to address the stormwater management system for the
northbound lane of North 271h Avenue, from Oak Street to Tschache Lane. This report will
determine the recommended sizing of the stormwater retention basins and conveyance facilities
within the northbound lane only. This report was prepared in accordance with the design criteria
set forth in the current edition of the City of Bozeman's Design Standards and Specifications
Policy.
Proiect Overview
This portion of North 27t"Avenue is being constructed in conjunction with the Fellowship
Baptist Church project, bounded on the west by North 271h Avenue, on the east by the proposed
North 25th Avenue, on the north by Tschache Lane and on the south by Oak Street.North 27th
Avenue is classified as a collector in the Bozeman Transportation Plan.
Preliminary Conditions Summary
The pre-development condition of the proposed North improvements is agricultural with no
residential structures on site. North 27th Avenue is currently being constructed from Oak Street
to Baxter Lane, with the southbound lane for the entire distance and the northbound lane from
Tschache Lane to Baxter Lane being constructed by others. The current topography of the site
can be generalized as flat with a consistent slope of approximately 1.4%from south to north.
Basis of Calculations
The calculations and recommendations within this report are based on the regulations set forth in
the City of Bozeman Design Standards and Specifications Policy. The Rational Method was
used to determine the pre-developed release rate and, in turn, the post-developed minimum
required storage volume. All calculations associated with the release rate and required storage
volumes were based on a 10-year, 2-hour storm event. The conveyance facilities, described
further in this report, are based on a 25-year, 2-hour storm event. Calculations are provided in
the appendix of this report.
Stormwater Retention
The proposed system will discharge from North 271h Avenue eastward to the adjacent property
prior to Tschache Lane. Stormwater retention is proposed for this property (Fellowship Baptist
Church). Stormwater retention facilities for the church are being designed by others. HKM
understands that these facilities will include retention storage for post development runoff from
North 27th Avenue.
Page 3 of 7
North 27th Avenue—Stormwater Investigation August, 2006
The site has been analyzed as a single runoff basin. A summary of the pre-developed peak runoff
rate and the post-developed required storage is shown below in Table 1.
Table 1
North 27th Avenue
—Oak Street to Tschache Lane(Northbound Lane)—
Stora a Re uirements
Pre-Developed Post-Developed
Peak Runoff Rate cfs Min. Required Storage ft3
0.50 2,497
The drainage basis is 0.94 acres in size, and composed entirely of the paved northbound lane of
North 27th Avenue and the east half of the raised median. For purposes of this calculation, the
entire area is assumed to be pavement in the post-development analysis. Runoff from the basin
flows north and will be collected in standard storm drain inlets (COB Standard Drawing 02720-1
and 02720-1B)at three locations. Proposed inlet locations are shown on Figure 1. The calculated
minimum storage volume for runoff from North 27th Avenue is 2,497 cubic feet, under
developed conditions.
Page 4 of 7
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North 27`h Avenue—Stormwater Investigation August, 2006
Stormwater Treatment and Release
The Stormwater retention ponds for the adjacent Fellowship Baptist Church property are being
design by others. Thus, stormwater treatment and release is not addressed here.
Conveyance Facilities
Stormwater runoff from this site will be conveyed to stormwater retention ponds by means of
curb and gutter, catch basins and storm main. All conveyance facilities on the site have been
sized to handle the 25-year, 2-hour storm event as required in the City of Bozeman Design
Standards and Specifications Policy. Table 2 summarizes the post-developed runoff rate and
required pipe diameter. The storm sewer mains are shown on Figure 1.
The PVC storm mains are the minimum required 15"diameter. The rational method and
Manning's Equation were used to size the storm main. All calculations can be found in the
Appendix of this report.
Standard 36"standard storm drain inlets (C.O.B Standard Drawing No. 02720-1)will be used to
capture the stormwater runoff at the points specified on Figure 1.
Table 2
North 27`h Avenue
—Oak Street to Tschache Lane (Northbound Lane)—
Conveyance Capacity
Post-Developed Pipe Diameter Pipe Capacity
Runoff Rate cfs in cfs
1.97 15 4.09
Page 6 of 7
North 271h Avenue—Stormwater Investigation August, 2006
Maintenance
The storm drainage system within the publicly dedicated right-of-way is defined as a public
system. The public system shall be maintained by the City of Bozeman. The private system,
those facilities that do not lie within the publicly dedicated right-of-ways, will be maintained by
the property owner.
Due to sediment in the storm runoff and other variables, regular maintenance will be required by
the City to maintain proper performance of the storage and drainage network. The following
steps are minimum requirements for the maintenance of the storm facilities.
A) Inspection Program—On an annual basis, the following elements of the storm water
facilities should be inspected for excessive sediment deposits:
1) Catch Basins
2) Curb Cut Openings
3) Storm Mains
4) Detention/Retention Ponds
B) Maintenance Program—The following maintenance measures should be completed
based on the inspection program:
1) Catch Basin, & Curb Cut Openings—excessive sediments shall be removed either
manually(with a shovel)or with a vacuum truck and flushed.
2) Storm Mains—Mains shall be flushed if necessary.
3) Detention/Retention Ponds—A stake will be set six(6) inches above the original
bottom of the basin. If sediment is over the stake, it must be removed and the basin
must be revegetated according to the original landscape plan.
Conclusion
This report establishes the projected stormwater flows, retention requirements and conveyance
recommendations for the northbound lane of North 27th Avenue (Oak Street to Tschache Lane).
These facilities will be constructed in conjunction with improvements to property owned by
Fellowship Baptist Church, located at the intersection of Oak Street and North 271h Avenue in
Bozeman.
Page 7 of 7
P
PEAK RUNOFF RATE P
AND RETENTION POND
VOLUME CALCULATIONS
D
I
X
North 27th Avenue Storm Drainage Fellowship Baptist Church
04C364.102 Retention Volume Calculations Bozeman , MT
Drainage Basin -North 27th Avenue ROW(Oak St to Tschache Ln)
The following calculations were used to determine the minimum required storage volume for storm
water runoff. The volumes were calculated using the Rational Method, and the retention facilities were
sized based on a 10-year 2-hour storm event.
Area= 0.94 Acre
C= 0.9 Impervious
I = 0.41 in./hr.
Determine post-developed runoff rate:
Q = C x I x A
0.34686 cfs
Determine minimum required storage volume:
V= 7200xQ
2497.392 cf
E NO IN E E R ING
Appendix A Page 1 of 1
FACILITY
CONVEYANCE P
CALCULATIONS
D
X
B
North 27th Avenue Storm Drainage Fellowship Baptist Church
04C364.102 Retention Volume Calculation Bozeman, MT
Storm Drainage Main-North 27th Avenue
The following calculations were used to size the conveyance facilities for stormwater runoff.
The volumes were calculated using the Rational Method,and the conveyance facilities were
sized based on a 25-year 2-hour storm event.
Contributing Basin(s)
A= 0.94 Acre
C= 0.9 Paved Roadway
Calculate Time of Concentration(Tc)
Developed Conditions:
S= 1.40%
0.9 Paved Roadway
Find Sheet/Shallow Concentrated Tc
Assume: L=700 ft. (300 ft-sheet flow/400 ft-shallow flow)
From Figure 1-1,Tc(SF)= 10 min.
Find Channel Flow Tc(Gutter Flow)
Using Mannings Equation, n=0.013,S= 1.4%,calculate channel flow
L= 550 ft
R= 0.92 ft
v= 11.09 ft/sec
Tc(cF)= 0.83 min
Find Total Tc
Tc=Tc(SF)+Tc(cF)
Total Tc(easin F)= 10.83 min
CalculatePre-developed Storm Intensity at Tc
From Figure 1-3, using the 25 year event, I=0.78Tc-°_64
I= 2.33 in/hr
Calculate Post-developed Peak Runoff Rate
Q= ciA, using the above parameters.
Q= 1.97 cfs
Calculate Pipe Capacity Provided
Q=(1.486/n)*A"R"'S"
Given: n= 0.013 Pipe Diameter=15"
A= 1.22718 sf Material=PVC
R= 0.31250 ft
S= 0.00400 ft/ft
Q= 4.08553 cfs> 1.97 cfs ok
V= 3.32919 fps
Appendix B 1 of 1