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MEADOW CREEK SUBDIVISION PHASE I
TO PROVIDE STREET, SANITARY SEWER,WATER EN6INEERINQr, INC.
Ia I AND STORM DRAIN IMPROVEMENTS A Consulting Engineers and Land Surveyors
!�4 BOZEMAN. MONTANA u-mod
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Appendix H:
Meadow Creek sub Ph I
,Stormwater Design Report
ENGIIIEERIN G INC .
A Consulting Engineers and Land Surveyors ��IFta)_ O � 2006
l.,LD �J l._3� .
STO RM WATER MANAGEMENT
DESIGN RE"�'Offf
FOR
Meadow Creek Subdivision, Phase I
Bozeman, Montana
Prepared For:
Meadow Creek Partners, LLC
924 Stoneridge Drive, Suite 1
Bozeman, MT 59718
February 2006
BOZ-05021.02
705 Osterman Drive, Suite F
Bozeman,MT 59715
Phone 406.522.9876
Fax 406.922.2768
info.bozeman@enginc.com
www.enginc.com
STORM WATER MANAGEMENT
DESIGN REPORT
FOR
Meadow Creek Subdivision, Phase I
Bozeman, Montana
Prepared For:
Meadow Creek Partners,LLC
924 Stoneridge Drive,Suite 1
Bozeman,MT 59718
Prepared By:
—11SUlling Engineers and Land Surveyors
MA
BILLINGS ■ BOZEMAN
February 2006
Boz-05021.02
TABLE OF CONTENTS Pg.
Introduction................................................................................................... 1
Site Location and Description.............................................................................. 1
ExistingConditions.......................................................................................... 1
Soils................................................................................................... 1
Drainage.............................................................................................. 2
DesignMethodology......................................................................... .............. 2
Design Considerations.............................................................................. 2
Subbasin Information............................................................................... 2
Storm Runoff Calculations................................................................................. 3
Rational Method Calculations..................................................................... 3
Gutter and Inlet Capacity Calculations........................................................... 3
Pipe Sizing Calculations............................................................................ 5
Detention Pond Calculations....................................................................... 6
Summary...................................................................................................... 7
References.................................................................................................... 8
LIST OF APPENDICES
Appendix A—Soils Information
Appendix B—Inlet Calculations
Appendix C—Pipe Sizing Calculations
Appendix D— Stormwater Service Lots Calculations
Appendix E—Gutter Capacity Calculations
Appendix F—Detention Pond Calculations
Appendix G—Outfall Structure Sizing
LIST OF TABLES
Table 1 —Rational Method Detention Basin Sizing (10-Year Design Storm)...................... 3
Table 2—Rational Method Inlet Basin Results (25-Year Design Storm)........................... 3
Table 3 —Inlet Capacity Summary: 25-Year Design Storm.......................................... 4
Table 4—Pipe Sizing Summary: 25-Year Design Storm............................................. 5-6
Table 5 —Detention Pond Sizing Summary: 1 0-Year Design Storm................................ 6
P:PM\BOZ-05021-02_STORIVI-DESIGN-RF-PORT I
INTRODUCTION
This design report summarizes the management plan for storm water runoff within Meadow Creek
Subdivision,Phase I located in Bozeman,Montana.The information contained in this report
provides the basis of design for the required storm drainage improvements to be completed.
The methodology and analysis procedures utilized in this report are in conformance with the design
standards found in the City of Bozeman Design Standards and Specifications Policy,March 2004.
Recommendations made in this report are based on these standards and the professional judgment
of the author.
SITE LOCATION AND DESCRIPTION
Phase I of Meadow Creek Subdivision is located on Certificate of Survey No. 2286. Generally, the
property is bordered on the east by Minor Subdivision 235; Genesis Business Park to the north;
vacant,undeveloped land to the west;and future phases of Meadow Creek Subdivision to the south.
Phase I of the development will contain four high-density lots with approximately thirty-five
dwelling units per lot.There are two proposed local streets and one collector to serve Phase I. The
two local streets are an extension of Enterprise Boulevard and Stubble Lane. The proposed
collector is Graf Street which will be extended east to connect to South 19`h Avenue. Each of the
internal local and collector streets will be constructed to City of Bozeman standards,having
appropriate right-of-way widths of 60-feet and 90-feet respectively,and street widths of 33-feet and
48-feet from back-of-curb to back-of-curb respectively. Boulevard sidewalks,located seven and a
half feet behind curb and gutter,will be installed at the time building construction occurs on the lots.
EXISTING CONDITIONS
Soils
According to the Soil Survey of Gallatin Couno Area,Montana (1996),the natural soil type is
predominantly Turner Loam and Meadowcreek Loam. Groundwater in the development area is as
high as 18-inches below the natural surface to 8 feet below the surface. Dewatering techniques will
be used during construction to control groundwater.
The site soils are gently sloping with moderate organic-matter content. The risk of soil blowing and
water erosion is moderate to low.The existing area is primarily rangeland, having a moderate cover
of native vegetation.A brief summary of the soils located in the subdivision is located in Appendix
A of this report. A more detailed description of the soils in this development can be found in the
Geotechnical Report for Meadow Creek Subdivision (December 2005,Allied Engineering Services,
Inc.).
P:PM\BOZ-05021_02_STORM_DESIGN_REPORT 1 02/22/2006
Drainage
The existing ground is sloped,having an approximate 2%gradient from south to north. Surface
runoff currently drains to existing creeks that run from south to north through Phase I of die
development. Some runoff drains via sheet flow to the northern boundary of the development and
eventually finds its way to the creeks that flow to the north from the property. Runoff from
adjacent property to the east and west flows to the north and does not enter Phase I of the
subdivision. Runoff from the southern boundary of Phase I flows to the existing creeks which flow
through the development from south to north.
DESIGN METHODOLOGY
Design Considerations
Phase I of Meadow Creek Subdivision has a gross area of 23.91 Acres. It is proposed to utilize a
system of inlets and storm drain piping to collect storm water runoff from Meadow Creek
Subdivision,Phase I. The storm drain piping will connect to detention areas located in two areas in
Phase 1. The detention areas will be designed to release only the pre-developed runoff from the 10-
year design storm event. In addition to Phase I of Meadow Creek Subdivision,other phases of the
subdivision will contribute to runoff to be collected in one of the two detention ponds located on
Phase I. Runoff from the contributing basins has been included in the analysis to properly size the
detention pond as well as the conveyance system which feeds the pond. Some of the area in Phase I
will be park and wetland area which will remain in pre-developed runoff condition and therefore this
area was not analyzed as part of this report. A stormwater exhibit has been included which
delineates the drainage basins that drain to the two detention ponds and the inlet basins that drain to
the inlet locations.
The detention ponds located in Phase I have been sized using the 10-year design storm event with
pre-development runoff as required by the City of Bozeman Design Standards and Specifications
Policy. All conveyance systems including gutters,inlets, and pipe have been sized to accept the 25-
year design storm as required by the City of Bozeman Design Standards and Specifications Policy.
The Rational method was used in calculating the storm runoff from the proposed development and
all contributing areas.
Subbasin Information
The storm water runoff analysis area for Meadow Creek Subdivision, Phase I has two drainage
basins which drain to two detention pond areas. These two drainage basins have been divided up
into smaller inlet basin areas. The inlet basin areas were used to space inlets and calculate the
needed conveyance system to accept the 25-year design storm. These basins can be seen on the
stormwater exhibit that is included in this report.
P:PM\BOZ-05021_02_STOR.i4.DESIGN_REPORT 2 02/22/2006
STORM RUNOFF CALCULATIONS
Rational Method Calculations
Storm water runoff calculations were performed using the Rational Method as outlined in the City
of Bozeman Design Standards and Specifications Policy. A Rational Method"C" factor of 0.50 was
taken from the Design Standards and Specifications Policy for basins that contained dense
residential lots and 0.35 for basins that contained low to medium density residential lots. The "C"
factor of 0.60 used for basins that contained only right-of-way area was taken from a weighted
average of"C" factors contained in HydmlogicAna#sis and Design, Second Edition (McCuen). Table 1
and Table 2 summarize the results of the Rational Method calculations used to size the detention
ponds and the conveyance systems in Phase I of Meadow Creek Subdivision. More detailed
calculations can be found in Appendix B and Appendix F of this report.
Table 1 Rational Method: Detention Basin Sizing (10-Year Design Storm)
Drainage Basin Area (Acre) "C" Factor Required Storage (cl)
14 16.26 0.50 11,396
4 35.42 0.35 14,005
Table 2 Rational Method: Inlet Basin Results (25-Year Design Storm)
Inlet Basin Area (Acre) "C" Factor Peak Runoff(efs)
14A 2.94 0.60 2.71
14B 1.02 0.50 0.66
14C 1.04 0.60 2.14
14D 1.02 0.60 1.46
4A 1.53 0.60 2.81
4B 4.87 0.35 2.60
4C 5.92 0.35 3.45
4D 9.19 0.35 5.13
4E 2.66 0.35 1.56
4F 1.36 0.60 2.09
4G 5.49 0.35 3.13
4H 0.76 0.60 1.39
Gutter and Inlet Capacity Calculations
The City of Bozeman Design Standards and Specifications provides that for city streets, the flow in
the gutters shall not be greater than 0.15 feet below the top of the curb. Calculations for available
gutter capacity for various street locations are located in Appendix K These gutter capacities were
used to place inlets at needed locations on the gutter.
P:PM\BOZ-05021_02_STORM_DESIGN_REPOR7I' 3 02/22/2006
Type III inlets are to be installed in basins where the inlets are on-grade. Inlet capacities for the on-
grade inlets were determined using dimensional data for a Neenah Foundry R-3278-AL inlet and the
following:
Q = K&/s
Q = captured flow (cfs)
K= inlet grate coefficient from Neenah Foundry K-charts
d = flow depth of runoff at inlet (ft)
Type II inlets will collect any flow directed to low points in the gutter. The capacity of the inlet was
calculated using a gutter depth of 0.35 feet (0.15 feet below top of curb). Using the nomograph
contained in the Neenah Foundry Company Catalog"R", 1 Vh Edition (R-3150 inlet), the inlet
capacities for the Type II inlet was determined to be 3.1 cubic feet per second. This capacity was
used to determine spacing and density of inlets at low points in the gutter.
The calculated capacities for the inlets proposed within Meadow Creek Subdivision,Phase I are
summarized in Table 3. More detailed calculations for the inlet capacities can be found in Appendix
B.
Table 3 Inlet Capacity Summary: 25-Year Design Storm
Total Theoretical Flow Allowable
Flow Captured By-Pass Gutter
Down- To Flow Into From Flow
Inlet stream Subbasin Inlet Inlet Inlet At Inlet
Inlet Type Inlet# Area (cfs) (cfs) (cfs) (cfs)
B1 Ponded NA Inlet Basin 14A 2.71 2.71 0.00 3.10
B2 Ponded NA Inlet Basin 14D 1.46 1.46 0.00 3.10
H1 Ponded NA Inlet Basin 14B 0.66 0.66 0.00 3.10
H2 Ponded NA Inlet Basin 14C 2.14 2.14 0.00 3.10
I1 Ponded NA Inlet Basin 4G 3.13 3.13 0.00 3.10
I2 Ponded NA Inlet Basin 4H 1.39 1.39 0.00 3.10
K1 On-Grade Il Inlet Basin 4E 1.94 1.94 0.00 4.09
1<2 On-Grade NA Inlet Basin 4F 2.25 2.25 0.00 4.09
01 On-Grade K1 Inlet Basin 4A 2.81 2.43 0.38 4.09
02 On-Grade K2 Inlet Basin 4B 2.60 2.43 0.16 4.09
P1 Ponded NA Inlet Basin 4C 3.45 3.10 0.35 3.10
P2 Ponded NA Inlet Basin 4C 0.35 0.35 0.00 3.10
Q1 Ponded NA Inlet Basin 4D 5.13 3.10 2.03 3.10
Q2 Ponded N:1 Inlet Basin 4D 2.03 2.03 0.00 3.10
P:PM\BOZ-05021._02_STORM_DESIGN_REPORT 4 02/22/2006
Pipe Sizing Calculations
Design of the system to convey storm water runoff for Meadow Creek Subdivision, Phase I included
analysis of the 25-year storm event as required by the City of Bozeman Design Standards and
Specifications Policy. The system was designed to accommodate the 25-year event, conveying runoff
captured by the system inlets to detention ponds.
Design calculations were performed by direct application of the Manning Equation. The minimum
pipe diameter for the storm drain main lines (non-service) shall be 12-inches. Service lines will
provide four lots (Block 2,Lots 1-3 and Block 4,Lot 5)with storm drain service. Calculations for
the flow generated from these lots can be found in Appendix D. The calculated piping system is
summarized in Table 4. Actual design slopes are greater than or equal to the minimum slopes in
Table 4 More detailed calculations of the piping system can be found in Appendix C.
Table 4 Pipe Sizing Summary: 25-Year Design Storm
Pipe Location Diameter Pipe Slope Pipe Capacity Flow in Pipe
From To (inches) (ft/ft) (efs) (cfs)
Inlet H1 MH H 12 0.005 2.519 0.660
Inlet H2 MH H 12 0.005 2.519 2.142
MH H MH G 15 0.0108 6.713 2.803
MH G MH F 15 0.0117 6.987 2.803
MH F MH E 15 0.0127 7.280 2.803
MH E MH D 15 0.0065 5.208 2.803
MH D MH C 15 0.0065 5.208 2.803
MH C MH B 15 0.0065 5.208 2.803
Inlet B1 MH B 12 0.010 3.563 2.707
Inlet B2 MH B 12 0.010 3.563 1.459
MH B Outfall 18 0.005 7.428 6.968
Inlet Q1 Inlet Q2 12 0.010 3.563 3.100
Inlet Q2 MH Q 15 0.010 6.460 5.130
MH Q MH P 15 0.007 5.405 5.130
Inlet P1 Inlet P2 12 0.010 3.563 3.100
Inlet P2 MH P 12 0.010 3.563 3.450
MH P MH 0 18 0.007 8.789 8.580
Inlet 01 MH 0 12 0.010 3.563 2.434
Inlet 02 MH 0 12 0.010 3.563 2.434
MH O MH N 21 0.0075 13.722 13.447
MH N MH M 21 0.0083 14.436 13.450
MH M MH 1, 21 0.0174 20.901 13.450
MH L MH K 21 0.0165 20.353 13.450
Inlet K1 MH K 12 0.010 3.563 1.937
P:PM\BOZ-05021_02_STORM_DESIGN_REPORT 5 02/22/2006
Table 4 (Cont.)
Pipe Location Diameter Minimum Slope Pipe Capacity Flow in Pipe
From To (inches) (ft/ft) (cfs) (cfs)
Inlet K2 MH K 12 0.010 3.563 2.252
MH K MH j 24 0.0065 18.239 17.639
MH 1 MH I 24 0.0065 18.239 17.639
Inlet I MH I 12 0.010 3.563 3.131
Inlet I2 MH 1 12 0.010 3.563 1.395
MH I Out£all 24 0.010 22.622 22.165
Blk 2,Lot 3 Service 12 0.010 3.563 1.700
Blk 2,Lot 3 Service 12 0.010 3.563 1.900
131k 2, Lot 3 Sen-icc I? 0.010 3.563 1.650
BU( 2,Lot 3 Service 12 0.010 3.563 1.350
Detention Pond Sizing Calculations
There are two proposed detention ponds located in Phase I of Meadow Creek Subdivision.
These two ponds will detain storm runoff from the two drainage basins as shown on the
stormwater exhibit. The ponds were sized to hold the 10-year design storm event while releasing
only the pre-developed runoff from the basins. Both ponds were designed to allow for treatment
of the stormwater and have adequate surface area to allow for particle settling. Discharge
structures will be designed to limit the flow out of both ponds to the pre-developed runoff flow.
Sizing for the discharge structures can be found in Appendix G. Overflow areas for both ponds
will direct flow from storm events greater than the 10-year event to natural drainage areas.
Overflow during these events will not flood or damage any structures on the site. A summary of
the detention pond sizing calculations is in Table 5. More detailed detention pond calculations
can be found in Appendix F.
Table 5 Detention Pond Sizing Summary: 10-Year Design Storm
Detention Drainage Required Required Surface Area Pre-developed
Pond Basin Storage (cf) with 1.5 ft depth (so Runoff(cfs)
14 14 11,396 7,597 2.06
4 4 14,005 9,337 4.69
P:PM\BOZ-05021_02_STORM_DESIGN_REPORT 6 02/22/2006
SUMMARY
The included analyses and calculations show that the proposed storm water management system for
Meadow Creek Subdivision,Phase I will adequately store the 10-year storm event and adequately
convey the 25-year storm event.Available gutter capacity and the location and spacing of inlets will
limit encroachment of runoff on pavement surfaces to acceptable levels.The recommended pipe
sizes would effectively convey storm runoff from Meadow Creek Subdivision,Phase I to designated
detention areas.Therefore, the proposed storm water managements system meets the requirements
of the City of Bozeman Design Standards and Specifications Policy and will satisfy the needs of the
owner of the property.
P:PM\BOZ-05021_02_STORM_DESIGN_REPDXI' 7 02/22/2006
REFERENCES
1. McCuen, Richard H. (1998). I lydrologic Analysis anti Dcsig;n. Second ldirion. Upper Saddle
River,NJ: Prentice Hall.
2. City Engineering Division. Quly, 2005). Design Standards and Specificnrio►is Polic;. City of
Bozeman,Montana:Author.
3. Allied Engineering Services, Inc. (2005). Geotechnical Report,Meadow Creek Subdivision,
South 19ffi Avenue,Bozeman,Montana.:Author.
4. United States Department of Agriculture Soil Conservation Service;Natural Resources
Conservation Services; and Montana Agricultural Experiment Station. (1996). Soil Survey of
Gallatin County Area Nlontana.Washington,DC: U.S. Government Printing Office
P:PM\BOZ-05021_02_STORM_DESIGN_REPORT 8 02/22/2006
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