HomeMy WebLinkAbout016_StormWaterEngineeringReportEngineering Report
Stormwater Design
South University District Phase 3 –
Block 3
Site Plan Submittal
September 2022
Submitted to:
City of Bozeman Engineering Department
20 East Olive
Bozeman, MT 59715
Prepared by:
Stahly Engineering and Associates
851 Bridger Drive, Suite 1
Bozeman, MT 59715
(406) 522-9526
Stormwater Plan 1 10/5/2022
Engineering Report
Table of Contents
General Information and Design Criteria
Existing Site Conditions
Storm Drainage Plan Description
Estimation of Runoff
Sub Drainage Areas
Inlet Capacity
Retention Facilities
Outfall Structure Weir Sizing
Conveyance Capacity
Curb and Gutter
Facilities Maintenance
Figures and Tables
Figure 1. Vicinity Map
Figure 2. Stormwater Plan
UPDATED SUD Phase 3 Calculations
Table 2 UPDATED - Pond Outfall and Overflow Calculations
Table 4 UPDATED - Curb and Gutter Conveyance Calculations
Table 5 UPDATED - Runoff & Capacity Calc’s for SUD PHASE 3 (attached)
Table 6 UPDATED - South 19th Ave Spread Width Calcs (attached)
Table 7 UPDATED - Volume Calculations – Detention Pond (attached)
Table 8 Volume Calculations – Arnold Street - West Pond (attached)
Table 9 Volume Calculations – Arnold Street - East Pond (attached)
Stormwater Plan 2 10/5/2022
General Information and Design Criteria
The intent of this report is to provide an updated to the SUD Phase 3 Subdivision
infrastructure stormwater engineering report dated January 2020 and included as
attachment to this report. This report will demonstrate conformance to the
previously-designed, and partially-constructed stormwater infrastructure.
The proposed South University District Phase 3 Block 3 Development is located
southeast of the intersection of 19th Avenue and Stucky Road. This development will
consist of 256 residential units on an 18.85-acre lot.
With 8 different building types: 3BR Cottages, tuck-under townhouses, 2BR Cottages,
2BR Townhouses, 1BR Large Cottages, 1BR Small Cottages, 1BR Lofts, and 1BR
Carriage Houses. The intent of this project is to create 256 residential units over a
variety of building types to create a diverse neighborhood in a growing part of town
adjacent to the Montana State University campus.
Stormwater mitigation is achieved by using a compact, efficient stormwater
management design utilizing Low Impact Design (LID) methodology to mitigate the
impacts of stormwater runoff. The LID stormwater mitigation has been designed in
accordance with City of Bozeman Design Standards and Specifications Policy for
retention/infiltration facilities. Survivability of LID systems through conventional
development is difficult. Erosion control Best Management Practices (BMP’s) will be
utilized during construction to reduce the impacts of construction site runoff, until the
LID systems are constructed.
Plans are provided showing proposed grading, drainage flow paths, and stormwater
retention/infiltration details and locations.
The developer’s contact information is:
Capstone Collegiate Communities
Davis Maxwell
431 Office Park Drive
Birmingham, AL 35223
Water supply and wastewater treatment will be provided by the City of Bozeman’s
municipal systems. The system owner’s contact information is:
City of Bozeman Public Service Department
PO Box 1230
Bozeman, MT 59771-1230
The location of the South University District Phase 3, Block 3 Development is shown on
the Vicinity Map in Figure 1.
Stormwater Plan 3 10/5/2022
Figure 1. Vicinity Map, Bozeman, Montana
Existing Site Conditions
SUD Phase 3 Block 3 is a block parcel created by the South University District Phase 3
Major Subdivision. The SUD Block 3 development site was previously used
agriculturally prior to its subdivision development. The existing ground slopes north at
grades between 1-3%. Existing offsite drainage is minimal, if present it would flow west
to an existing irrigation ditch on the east side of 19th Avenue Right-of-Way and
Mandeville Creek, east to Mandeville Creek or north to an irrigation ditch on the south
side of Kagy Boulevard and either infiltrates or makes its way to Mandeville Creek.
Block 2 cannot utilize Mandeville Creek as an outfall due to the topography, creek
location and adjacent properties. The stormwater management facilities for the Block 3
Development were constructed during the SUD Phase 2 infrastructure project and
located in City Park 4, northeast of the Block 3 site.
A geotechnical evaluation was conducted and is provided in a separate appendix of this
submittal. This site is typical of Bozeman with fine-grained soils overlying gravel
deposits. Geotechnical borings have determined the depth to gravel ranges from 3.5 to
5 feet below existing grade.
Groundwater monitoring was conducted in 2019 and 2022 during the high groundwater
season for the SUD Phase 3 subdivision development. Groundwater monitoring found
groundwater depths ranged from 5.5’ to 10.0’ below existing grade in the areas of the
site proposed for development. The site is not located within a 100-year floodplain.
Stormwater Plan 4 10/5/2022
Storm Drainage Plan Description
The storm drainage plan for the SUD Phase 3 Block 3 site development consists of
conveying stormwater runoff to an existing retention basin in City Park 4 located
northeast of the intersection of Stucky Rd. and South 17th Ave. This pond has been
constructed as a part of the subdivisions “Common Subdivision Improvements (CSIs)”
and a 15” outfall flows to Mandeville Creek. The overall storm drainage plan for Block 3
is depicted on attached Figure 2. This plan shows proposed drainage basin areas, flow
paths, and retention/infiltration system locations. In general, grades will be sloped away
from buildings towards interior drive aisles. The sub drainage areas typically drain north
via curb and gutter that conveys runoff to inlets and storm drains connected to
retention/infiltration system located within the park. The site will be divided into 2
primary sub-drainage areas as shown on attached Figure 2 and described below.
Sub Drainage Area Description
Sub-drainage area 16B is located on the north half of the site and drains north to the
existing 24” storm drain stub on the south side of Stucky Road. Sub-area 16C is located
on the south half of the site and drains northeast to the proposed private Student Drive
which then conveys storm drainage to the proposed South 17th Avenue storm drainage
system. South 17th Avenue will be designed and constructed concurrently with the SUD
Phase 3 Block 3 project. Storm drains will be located within South 17th Avenue and
convey runoff to an existing 24” storm drain located on the south side of Stucky Road.
Future Arnold Street, which borders the southern boundary of the site, will also be
designed and constructed concurrently with the SUD Phase 3 Block 3 project. The
proposed Arnold Street will provide stormwater detention / infiltration basins to mitigate
its stormwater runoff. The detention / infiltration basins will be located at the southern
edge of the adjacent City Park which was created during the SUD Phase 3 subdivision
process.
Estimation of Runoff
Runoff estimates were obtained for each sub-drainage area using City of Bozeman
standards. The sites stormwater facilities have been sized to fully capture the 10-year,
2-hour storm event. The Bozeman IDF (Intensity, Duration, and Frequency) curves
show a rainfall intensity of 0.41 in/hour for the 10-year, 2-hour storm, totaling a 0.82-
inch storm event. The basin runoff calculations are displayed in the updated Table 3 for
the retention-destined basins, and the updated Table 5 for detention-destined basins.
These tables are included in the Appendix.
Inlet Capacity
The curb inlets on the roadways in the development were analyzed to ensure they have
capacity to accept flows conveyed to them without reaching a point 0.15 feet from the
top of the curb. The COB-approved Neenah Foundry R-3067-L inlet structure has a
Stormwater Plan 5 10/5/2022
capacity of 5.98 cfs at 0.35 feet of head (0.15 below top of curb). This capacity will
convey the necessary flows.
Retention Facilities
The exiting retention basin located in in City Park 4 was designed to account for the
stormwater runoff from SUD Block 3, as detailed in the updated Table 3 and Table 5 in
the attached appendix of this report. Two additional stormwater retention facilities are
proposed for the mitigation of stormwater runoff associated with the proposed Arnold
Street construction. The Arnold Street storm retention basins will be in the southern
edge of the adjacent City Park 3. They will be designed and included with the onsite
infrastructure submittal. Preliminary runoff calculations were made to size the basins
and are included in the updated Table 3 and Table 5 in the attached appendix. The
addition of the two Arnold Street stormwater basins reduces to overall drainage area to
the existing pond by approximately 2.29 acres from 28.19 acres to 25.90 acres.
Outfall Structure Weir Sizing
The Detention basin outflow is restricted by a typical control structure as depicted in
COB Standards Figure A-2. Using the weir calculation equation given in Section II.D.2
of the COB Standards, the slot width of the outlet structure was determined to be 8”.
The slot width limits the discharge from the structure to pre-developed rates at the
maximum pond depth of 1.5’. The pre-developed rate is estimated to be 3.54 cfs,
calculations are included in Table 5 of the appendix. In the occurrence of an event
greater than the 10-year event, the ponds are sized for the emergency overflow of the
ponds directs flow to the east to Mandeville Creek. The emergency overflow will be
sized for the 100-year, 2-hour event. The following table provides the outfall and
overflow calculations. Preliminary overflow calculations for the Arnold Street stormwater
basins are also provided below.
Table 2: Pond Outfall and Overflow Calculations.
Phase 3 Pond Outfall Weir Calcs Phase 3 Pond Overflow Weir Calcs
Pre-developed Runoff (cfs) 3.54 Post-developed Runoff (cfs) 43.19
Weir Coefficient "C" 3.33 Weir Coefficient "C" 3.33
Head (ft) 1.5 Head (ft) 0.75
Slot Width (in) 7 Overflow Width (ft) 20
Arnold Street West Outfall Weir Calcs Arnold Street West Outfall Weir Calcs
Pre-developed Runoff (cfs) 0.17 Post-developed Runoff (cfs) 4.46
Weir Coefficient "C" 3.33 Weir Coefficient "C" 3.33
Head (ft) 1.5 Head (ft) 0.75
Slot Width (in) 0 Overflow Width (ft) 2
Arnold Street East Outfall Weir Calcs Arnold Street East Outfall Weir Calcs
Pre-developed Runoff (cfs) 0.14 Post-developed Runoff (cfs) 3.64
Weir Coefficient "C" 3.33 Weir Coefficient "C" 3.33
Head (ft) 1.5 Head (ft) 0.75
Slot Width (in) 0 Overflow Width (ft) 2
Stormwater Plan 6 10/5/2022
Conveyance Pipe Capacity
Conveyance pipes were sized by adding the 25-year peak runoff rates of contributing
basins without routing or attenuation. The pipe size calculations are displayed in the
updated Table 5 of the Appendix.
Curb and Gutter
Curb and gutter is used on the site to direct runoff into the underground storm pipe
network. To ensure the standard curb design will provide adequate conveyance
capacity for peak flows, curb and gutter with the greatest flows and least amount of
redundant or secondary storm conveyance options was identified and analyzed for
conveyance capacity. The critical curb required to convey the maximum flow was
identified as the approximately 548’ length of curb running from south to north along S.
17th Ave, serving a catchment area of approximately 43124.4 sf. This catchment area
produces a peak flow of 2.36 cfs for the 25-year design storm. At the minimum slope of
0.5%, the curb on site has a conveyance capacity of 5.03 cfs.
Table 4 – Curb and Gutter Conveyance Calculations
Curb and Gutter Capacity Calcs
Max Curb Conveyance Req'd
(ft^3/sec) 2.36
Right-side Slope X:1 0.06
Left-side Slope X:1 33.00
Channel Bottom Width (ft) 0
Flow Depth (ft) 0.350
Flow Area (ft^2) 2.025
Wetted Perimeter (ft) 11.906
Width 0.044
Hydraulic Radius (ft) 0.170
Manning's Roughness 0.013
Slope (ft/ft) 0.005
Average Velocity (ft/sec) 2.49
Flow (ft^3/sec) 5.03
Stormwater Plan 7 10/5/2022
[It should be noted that the following Storm Water Maintenance plan was filed for
SUD Ph3, Block 3. The developer’s legal team are planning on amending the
Storm Water Maintenance Plan to include maintaining a piped irrigation ditch in
the Arnold Street ROW before it empties in the ‘Park 3’ lot and becomes
Mandeville Creek.]
Storm Water Maintenance Plan
The proposed storm drainage facilities will be privately operated and maintained by the
Property Owners Association (POA). The POA Covenants should include the following
stormwater maintenance provisions:
(a) General Information.
The South University District Phase 3 utilizes conventional stormwater collection
to mitigate storm water impacts. The stormwater facilities consist of curb and
gutter, curb inlets, sumped manholes, onsite and offsite conveyance piping,
underground retention chambers, and an existing offsite detention basin located
in the city park. The system is designed to accommodate all storm water from the
Property.
The storm water conveyance facilities located on the property are privately
owned and maintained. It is the property owner association's responsibility to
maintain the storm water facilities located on the property. The storm water
facilities are designed to operate without excessive maintenance. However, like
all infrastructure, periodic maintenance will prevent costly repair and
replacement. The maintenance plan set forth in this Section has been prepared
in accordance with City of Bozeman guidelines. Over time, recommended
maintenance guidelines may evolve. Please contact the City of Bozeman
Stormwater Division if any questions arise.
(b) Storm Water Facilities Maintenance Schedule.
(i) Site Housekeeping. Site housekeeping is to be conducted
continuously as needed. The main cause of storm water facility damage is
poor site housekeeping. Sediment tracked onto pavement can be washed
into storm water inlets/ conveyance piping and damage these facilities.
Trash can clog pipes and inlet structures causing property damage. Site
housekeeping consists of the following:
• Keep sidewalk and pavement areas clean.
• Pick up trash.
• Restore damaged landscaping in order to prevent sediment runoff.
(ii) System Monitoring: System monitoring is to be conducted quarterly,
except in winter. The storm water facilities shall be inspected quarterly to
Stormwater Plan 8 10/5/2022
quickly identify small issues before expensive damage can occur. In
addition to regular monitoring, the best time to inspect the performance of
storm water facilities is during runoff events. System monitoring consists
of the following:
• Observe system during runoff. Look for ponding outside of
stormwater inlets. This can indicate a clogged inlet or pipe.
• Inspect inlets, manholes and pipes.
(iii) Inlet, Manhole, and Piping Quarterly Maintenance: All stormwater
inlets and manholes have a sump to capture sediment. If this sediment is
not periodically removed it can wash downstream and clog infiltration
facilities. The sump is typically visible from the surface through the inlet
grate. Inlet, manhole, and piping maintenance consists of the following:
• Remove visible sediment from sump.
• Inspect pipe inlets and outlets for sediment in pipe and remove if
present.
(iv) Inlet, Manhole, and Piping Long-term Maintenance. This
maintenance is to be conducted long-term if and when necessary. If
regular housekeeping and maintenance is not performed adequately,
sediment and debris can accumulate in the stormwater conveyance
piping, and pipes may become clogged. Long-term inlet, manhole, and
piping maintenance consist of the following:
• Hiring a contractor to clean pipes and remove all sediment
encountered from manhole sumps, inlet sumps and/or piping.
(v) Retention Pond Long-term Maintenance. This maintenance is to be
conducted on an annual basis at a minimum. If regular housekeeping and
maintenance is not adequately performed, sediment and debris will
accumulate in the underground stormwater retention basins and could
negatively affect the stormwater percolation rate. Retention pond
maintenance consist of the following:
• Remove the underground chamber’s inspection port covers.
• Record the depth from the rim of the inspection port to the
chamber’s floor. If the measurement changes by 0.1’ between any
reading, or sediment accumulates to a depth of 0.1’ above the
bottom of the chamber,
• Hire a contractor to flush and clean out the stormwater storage
chambers.
SDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSOUTH 14TH AVESDSDSDSDSDSDSDSDSDSDWILLOW WAY
SD SDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSD SDSDSDSDSDSDSDSD
SOUTH 14TH AVESDSTUCKY RD(48' WIDTH - 90' ROW)SDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSDSD STATE ST(35' WIDTH - 60' ROW)SDSDSDSDSDEXISTING
TRAILS (TYP)S 19TH AVE(47' WIDTH - 70' ROW) SOUTH 17TH AVE(47' WIDTH - 70' ROW)SDSD
KAGY BLVD(ROW VARIES)
STUCKY RD(48' WIDTH - 90' ROW)
KAGY BLVD(ROW VARIES)
ARNOLD ST(35' WIDTH - 70' ROW)
SD
SD
SD
SOUTH 14TH AVESOUTH 17TH AVE(47' WIDTH - 70' ROW)(ROW WIDTH VARIES)S 19TH AVE(ROW WIDTH VARIES)S 19TH AVE(ROW WIDTH VARIES)SD
EXISTING
TRAILS (TYP)
EXISTINGTRAILS (TYP)STORM BASINSTORM
BASIN (47' WIDTH - 70' ROW) SOUTH 18TH AVESTUDENT DRIVES 19TH AVE(ROW WIDTH VARIES)EXISTING
STORM BASIN
CITY PARK 1
4.41 ACRES
PLAT J-605
Tract 3ACOS 2661BTract 1ACOS 2661B
CITY PARK 2
9.64 ACRES
PLAT J-605
LOT 1, BLOCK 1"PHASE 3"8.20 ACRESPLAT J-695
CITY PARK 4
1.83 ACRES
PLAT J-695
COMMON OPEN SPACELOT 1, BLOCK 1, 0.09 ACPLAT J-695COMMON OPEN SPACELOT 2, BLOCK 1, 0.07 ACPLAT J-695COMMON OPEN SPACELOT 1, BLOCK 2, 0.07 ACPLAT J-695 COMMON OPEN SPACELOT 2, BLOCK 2, 0.07 ACPLAT J-695
LOT 1, BLOCK 3
"PHASE 3"
18.85 ACRES
PLAT J-695
CITY PARK 3
13.36 ACRES
PLAT J-695
LOT 2 "PHASE 1"6.41 ACRESLOT 1, BLOCK 2
"PHASE 3"
8.60 ACRES
PLAT J-695
ARNOLD ST(35' WIDTH - 70' ROW) SOUTH 18TH AVESTUDENT DRIVE
SOUTH 17TH AVEARNOLD STS 19TH AVESTUCKY RD
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>STORM WATERBASIN 1 1.03AC GROSSSTORM WATERBASIN 30.36 AC GROSS STORM WATERBASIN 20.36 AC GROSS STORM WATER BASIN 60.32 AC GROSS
STORM WATER
BASIN 12
0.49 AC GROSS
STORM WATER
BASIN 11 0.44 AC
GROSS
STORM WATERBASIN 4 2.26 ACGROSS
STORM WATER
BASIN 13
3.96 AC GROSS
STORM WATER
BASIN 14
1.98 AC GROSS
STORM WATER
BASIN 9
0.85 AC GROSS
STORM WATER
BASIN 7
0.21 AC GROSS
STORM WATER
BASIN 10
0.94 AC GROSS
STORM WATER
BASIN 8
0.19 AC GROSS
STORM WATER
BASIN 15
0.97 AC GROSS
STORM WATER
BASIN 18
1.03 AC GROSS
STORM WATER
BASIN 17
1.26 AC GROSS
9A
14A
12B
15A8A7A
11A12A13B
13A
15B10A15C3A5A2A1B1A6ASTORM WATERBASIN 50.33 AC GROSS
16A17A
STORM WATER
BASIN 16B
7.73 AC GROSS
STORM WATER
BASIN 16 C
9.43 AC GROSS
STORM WATER
BASIN 16A
0.67 AC GROSS
16C16B
17B18A1 12/2/2021 DRAFT CONCEPT PLAN
2 1/27/2022 COB CONCEPT SUBMITTAL ZWL CDP
3 10/3/2022 SITE PLAN SUBMITTAL ZWL CDP PROFESSIONALENGINEERS &SURVEYORSSTAHLYENGINEERING& ASSOCIATESTHE COTTAGES AT
BOZEMAN
CAPSTONE COLLEGIATE
COMMUNITIES LLCFIGURE 2SUD PH3 BLOCK 3STORM DRAINAGEFIGURE
Table 5Runoff and Capacity Calculations for S 19th Ave & Campus BlvdInlet Drainage BasinInlet Basin 6 5 2 3 4 13 11 12 7 8 9 10 14 15 17 18 16A 16B 16C 4 17 18Land Use REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMU REMUDrainage Area (acres) 0.517 0.517 0.32 0.33 0.36 0.36 2.26 1.98 0.44 0.49 0.21 0.19 0.85 0.94 1.98 0.97 1.26 1.03 0.67 7.73 9.43 2.26 1.26 1.03Slope (%) 2 2 1.7 1.7 0.55 0.55 1.7 1.7 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 1.7 1.7 1.7Runoff Coefficients 0.8 0.8 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6Frequency Adjustment Factor, Cf 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1Basin Length (ft) 670 670 425 425 286 286 963 1322 283.5 283.5 97 66 380 380 430 430 344 421 350 350 350 963 648 435Time of Concentration (min) 8.5 8.5 7.1 7.1 8.5 8.5 6.0 10.0 5.0 5.0 5.0 5.0 5.0 5.0 10.0 10.0 8.0 8.0 10.0 10.0 10.0 6.0 5.0 5.0 MANUAL ESTIMATESPeak Flow CalculationsDesign Storm 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 25yr 100yr 100yr 100yrIntensity at Tc (Figure I-2 pg. 29) (in/hr) 2.73 2.73 3.05 3.05 2.73 2.73 3.40 2.46 3.83 3.83 3.83 3.83 3.83 3.83 2.46 2.46 2.83 2.83 2.46 2.46 2.46 4.72 5.34 5.34Peak Runoff Rate at Tc (Q = CIA) (cfs)1.13 1.13 0.78 0.81 0.79 0.79 4.62 2.92 1.01 1.12 0.49 0.44 1.95 2.16 2.92 1.43 2.14 1.75 0.99 11.39 13.89 6.41 4.04 3.30Detention Basin A - Pipe Network A CapacityPipe Number 1B 1A 6A 5A 2A 3A 15C 9A 10A 15A 14A 7A 8A 12B 11A 12A 13B 13A 16A 16B 16C 15B 17A 17A 18APipe Size (in) 15 15 15 15 15 15 36.00 15.00 15.00 24.00 15.00 15.00 15.00 30.00 15.00 24.00 24.00 18.00 18.00 24.00 24.00 30.00 15.00 18.00 18.00Manning's "n" (PVC) 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013 0.013Area (ft2)1.23 1.23 1.23 1.23 1.23 1.23 7.07 1.23 1.23 3.14 1.23 1.23 1.23 4.91 1.23 3.14 3.14 1.77 1.77 3.14 3.14 4.91 1.23 1.77 1.77Wetted Perimeter (ft) 3.93 3.93 3.93 3.93 3.93 3.93 9.42 3.93 3.93 6.28 3.93 3.93 3.93 7.85 3.93 6.28 6.28 4.71 4.71 6.28 6.28 7.85 3.93 4.71 4.71Hydraulic Radius (ft) 0.31 0.31 0.31 0.31 0.31 0.31 0.75 0.31 0.31 0.50 0.31 0.31 0.31 0.63 0.31 0.50 0.50 0.38 0.38 0.50 0.50 0.63 0.31 0.38 0.38Slope (ft/ft) 0.0100 0.0081 0.0100 0.0082 0.0096 0.0096 0.0022 0.0148 0.0100 0.0100 0.0100 0.0100 0.0134 0.0022 0.0153 0.0400 0.0022 0.0022 0.01000.0100 0.0100 0.0356 0.0050 0.0050 0.0050Full Flow Capacity (cfs)6.48 5.83 6.48 5.87 6.35 6.35 31.377.88 6.48 22.68 6.48 6.48 7.50 19.29 8.01 45.37 10.64 4.94 10.53 22.68 22.68 77.60 4.58 7.45 7.45Velocity (ft/sec) 5.28 4.75 5.28 4.78 5.17 5.17 4.44 6.42 5.28 7.22 5.28 5.28 6.11 3.93 6.53 14.44 3.39 2.80 5.96 7.22 7.22 15.81 3.73 4.21 4.21Contributing Inlet Basin 1 (1/2) 15623NONE 9 10 15 14 7 8 NONE 11 12 NONE 13 16A 16B 16B NONEStorm Pond 17 18Contributing Pipes 6A 12B 10A NONE 16C NONE NONE 7A 11A NONE 16B 13A NONE NONE NONE NONE 14A15B12A 16A 15A13BActual Pipe Flow (cfs) 2.26 1.13 0.78 1.59 0.79 0.79 25.26 4.11 2.16 15.32 2.92 0.49 0.93 7.03 1.01 2.11 3.90 2.92 0.99 11.39 13.89 18.24 3.86 4.04 3.30% Capacity 35% 19% 12% 27% 12% 12% 81% 52% 33% 68% 45% 8% 12% 36% 13% 5% 37% 59% 9% 50% 61% 24% 84% 54% 44%1
Table 6 S 19th Ave Spread Width Calcs
Inlet Basin 413
Drainage Area (acres) 2.26 1.98
Slope (%) 1.7 1.7
Runoff Coefficients 0.6 0.6
Frequency Adjustment Factor, Cf 1.1 1.1
Basin Length (ft) 963 1322
Time of Concentration (min) 6.0 10.0
Peak Flow Calculations
Design Storm 25yr 25yr
Intensity at Tc (Figure I-2 pg. 29) (in/hr) 3.40 2.46
Peak Runoff Rate at Tc (Q = CIA) (cfs)4.62 2.92
Spread Width Calculations
Right-side slope X:1 (curb face) 0.05
Left-side slope X:1 (asphalt) 50.00
Channel bottom width (ft) 0
Flow Depth (ft) 0.254
Flow Area (ft^2) 1.615
Wetted Perimeter (ft) 12.957
Width 12.700
Hydraulic Radius (ft) 0.125
Manning's Roughness 0.013
Slope (ft/ft) 0.010
Average Velocity (ft/sec) 2.86
Flow (ft^3/sec) 4.61
Spread Width Length (ft) 12.7
Table 7 23462
Volume Calculations - Detention Pond 18683
21073
Time of Concentration Calculations Preconstruction Postconstruction torm Sewer Flow 1.50
Land Use Open Land REMU REMU 31609
Drainage Area (acres) 25.90 25.90 25.90
Slope (%) 2.1 2.1 2.1
Runoff Coefficients 0.2 0.6 0.6
Frequency Adjustment Factor, Cf 1 1 1.1
Basin Length (ft) 1700 425 425 Basin length based on typical inlet area
Time of Concentration (min) 54.2 15.1 13.2
0.5" storm volume (cf) 9401.7 28205.1 28205.1
Peak Flow Calculations
Design Storm 10-Year 10-Year 25-Year 100-year MAX VOL.
Intensity at Tc (Figure I-2 pg. 29) (in/hr) 0.68 1.57 2.05 2.78 23055.02
Peak Runoff Rate at Tc (Q = CIA) (cfs)3.54 24.43 31.87 43.19
(max release rate)
Required Storage Volume
Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage
(minutes) (in/hr) (Q = CIA) (cfs) (cf) (cf) (cf)
2 5.84 90.73 10887.82 425.06 10462.76
4 3.72 57.82 13877.19 850.13 13027.07
6 2.86 44.43 15993.13 1275.19 14717.94
8 2.37 36.85 17687.32 1700.25 15987.07
10 2.05 31.87 19124.08 2125.31 16998.77
12 1.82 28.31 20384.21 2550.38 17833.84
14 1.65 25.61 21514.21 2975.44 18538.77
16 1.51 23.48 22543.56 3400.50 19143.06
18 1.40 21.75 23492.32 3825.56 19666.76
20 1.31 20.31 24374.80 4250.63 20124.17
24 1.16 18.04 25980.92 5100.75 20880.17
26 1.10 17.13 26719.06 5525.81 21193.25
28 1.05 16.32 27421.16 5950.88 21470.29
30 1.00 15.61 28091.37 6375.94 21715.44
32 0.96 14.97 28733.14 6801.00 21932.14
34 0.93 14.39 29349.33 7226.06 22123.26
36 0.89 13.86 29942.39 7651.13 22291.26
38 0.86 13.38 30514.40 8076.19 22438.21
40 0.83 12.94 31067.16 8501.25 22565.91
42 0.81 12.54 31602.24 8926.31 22675.92
44 0.78 12.17 32120.99 9351.38 22769.62
46 0.76 11.82 32624.64 9776.44 22848.20
48 0.74 11.50 33114.25 10201.50 22912.75
50 0.72 11.20 33590.78 10626.57 22964.21
52 0.70 10.92 34055.07 11051.63 23003.44
54 0.69 10.65 34507.89 11476.69 23031.20
56 0.67 10.40 34949.93 11901.75 23048.18
58 0.65 10.17 35381.83 12326.82 23055.02 Required Storage
60 0.64 9.95 35804.16 12751.88 23052.28
62 0.63 9.74 36217.43 13176.94 23040.49
64 0.61 9.54 36622.13 13602.00 23020.12
66 0.60 9.35 37018.68 14027.07 22991.61
68 0.59 9.17 37407.50 14452.13 22955.37
70 0.58 9.00 37788.95 14877.19 22911.76
72 0.57 8.83 38163.39 15302.25 22861.13
74 0.56 8.68 38531.12 15727.32 22803.81
76 0.55 8.53 38892.45 16152.38 22740.07
78 0.54 8.39 39247.65 16577.44 22670.21
80 0.53 8.25 39596.98 17002.50 22594.47
82 0.52 8.12 39940.67 17427.57 22513.11
84 0.51 7.99 40278.96 17852.63 22426.34
86 0.51 7.87 40612.06 18277.69 22334.37
88 0.50 7.75 40940.16 18702.75 22237.40
90 0.49 7.64 41263.44 19127.82 22135.62
92 0.48 7.53 41582.09 19552.88 22029.21
94 0.48 7.43 41896.26 19977.94 21918.32
96 0.47 7.33 42206.13 20403.00 21803.12
98 0.47 7.23 42511.82 20828.07 21683.75
100 0.46 7.14 42813.48 21253.13 21560.35
102 0.45 7.04 43111.25 21678.19 21433.06
104 0.45 6.96 43405.25 22103.26 21301.99
106 0.44 6.87 43695.59 22528.32 21167.27
108 0.44 6.79 43982.39 22953.38 21029.01
110 0.43 6.71 44265.77 23378.44 20887.32
112 0.43 6.63 44545.81 23803.51 20742.30
114 0.42 6.55 44822.62 24228.57 20594.05
116 0.42 6.48 45096.29 24653.63 20442.66
118 0.41 6.41 45366.92 25078.69 20288.22
120 0.41 6.34 45634.57 25503.76 20130.82
Notes
Table 8
Volume Calculations - Arnold Street Detention Pond - West
Time of Concentration Calculations Preconstruction Postconstruction Storm Sewer Flow
Land Use Open Land REMU REMU
Drainage Area (acres) 1.26 1.26 1.26
Slope (%) 2.1 2.1 2.1
Runoff Coefficients 0.2 0.8 0.8
Frequency Adjustment Factor, Cf 1 1 1.1
Basin Length (ft) 1700 425 425 Basin length based on typical inlet area
Time of Concentration (min) 54.2 9.0 6.6
0.5" storm volume (cf) 457.4 1829.5 1829.5
Peak Flow Calculations
Design Storm 10-Year 10-Year 25-Year 100-year MAX VOL.
Intensity at Tc (Figure I-2 pg. 29) (in/hr) 0.68 2.19 3.20 4.42 1746.00
Peak Runoff Rate at Tc (Q = CIA) (cfs)0.17 2.21 3.22 4.46
(max release rate)
Required Storage Volume
Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage
(minutes) (in/hr) (Q = CIA) (cfs) (cf) (cf) (cf)
2 5.84 5.89 706.24 20.68 685.56
4 3.72 3.75 900.14 41.36 858.78
6 2.86 2.88 1037.39 62.04 975.36
8 2.37 2.39 1147.29 82.71 1064.57
10 2.05 2.07 1240.48 103.39 1137.09
12 1.82 1.84 1322.22 124.07 1198.15
14 1.65 1.66 1395.52 144.75 1250.77
16 1.51 1.52 1462.29 165.43 1296.86
18 1.40 1.41 1523.83 186.11 1337.72
20 1.31 1.32 1581.07 206.79 1374.28
24 1.16 1.17 1685.25 248.14 1437.10
26 1.10 1.11 1733.13 268.82 1464.31
28 1.05 1.06 1778.67 289.50 1489.17
30 1.00 1.01 1822.14 310.18 1511.96
32 0.96 0.97 1863.77 330.86 1532.91
34 0.93 0.93 1903.74 351.54 1552.20
36 0.89 0.90 1942.21 372.22 1569.99
38 0.86 0.87 1979.31 392.90 1586.42
40 0.83 0.84 2015.17 413.57 1601.59
42 0.81 0.81 2049.87 434.25 1615.62
44 0.78 0.79 2083.52 454.93 1628.59
46 0.76 0.77 2116.19 475.61 1640.58
48 0.74 0.75 2147.95 496.29 1651.66
50 0.72 0.73 2178.86 516.97 1661.89
52 0.70 0.71 2208.98 537.65 1671.33
54 0.69 0.69 2238.35 558.33 1680.02
56 0.67 0.67 2267.02 579.00 1688.02
58 0.65 0.66 2295.04 599.68 1695.36
60 0.64 0.65 2322.43 620.36 1702.07
62 0.63 0.63 2349.24 641.04 1708.20
64 0.61 0.62 2375.49 661.72 1713.77
66 0.60 0.61 2401.21 682.40 1718.81
68 0.59 0.59 2426.43 703.08 1723.36
70 0.58 0.58 2451.18 723.76 1727.42
72 0.57 0.57 2475.46 744.43 1731.03
74 0.56 0.56 2499.32 765.11 1734.20
76 0.55 0.55 2522.75 785.79 1736.96
78 0.54 0.54 2545.79 806.47 1739.32
80 0.53 0.54 2568.45 827.15 1741.30
82 0.52 0.53 2590.75 847.83 1742.92
84 0.51 0.52 2612.69 868.51 1744.18
86 0.51 0.51 2634.30 889.19 1745.11
88 0.50 0.50 2655.58 909.86 1745.71
90 0.49 0.50 2676.55 930.54 1746.00 Required Storage
92 0.48 0.49 2697.22 951.22 1746.00
94 0.48 0.48 2717.60 971.90 1745.70
96 0.47 0.48 2737.69 992.58 1745.12
98 0.47 0.47 2757.52 1013.26 1744.27
100 0.46 0.46 2777.09 1033.94 1743.15
102 0.45 0.46 2796.41 1054.61 1741.79
104 0.45 0.45 2815.48 1075.29 1740.18
106 0.44 0.45 2834.31 1095.97 1738.34
108 0.44 0.44 2852.91 1116.65 1736.26
110 0.43 0.44 2871.29 1137.33 1733.96
112 0.43 0.43 2889.46 1158.01 1731.45
114 0.42 0.43 2907.41 1178.69 1728.73
116 0.42 0.42 2925.16 1199.37 1725.80
118 0.41 0.42 2942.72 1220.04 1722.67
120 0.41 0.41 2960.08 1240.72 1719.36
Notes
Table 9
Volume Calculations - Arnold Street Detention Pond - East
Time of Concentration Calculations Preconstruction Postconstruction Storm Sewer Flow
Land Use Open Land REMU REMU
Drainage Area (acres) 1.03 1.03 1.03
Slope (%) 2.1 2.1 2.1
Runoff Coefficients 0.2 0.8 0.8
Frequency Adjustment Factor, Cf 1 1 1.1
Basin Length (ft) 1700 425 425 Basin length based on typical inlet area
Time of Concentration (min) 54.2 9.0 6.6
0.5" storm volume (cf) 373.9 1495.6 1495.6
Peak Flow Calculations
Design Storm 10-Year 10-Year 25-Year 100-year MAX VOL.
Intensity at Tc (Figure I-2 pg. 29) (in/hr) 0.68 2.19 3.20 4.42 1280.50
Peak Runoff Rate at Tc (Q = CIA) (cfs)0.14 1.81 2.63 3.64
(max release rate)
Required Storage Volume
Storm Duration Intensity Future Runoff Rate Runoff Volume Release Volume Required Storage
(minutes) (in/hr) (Q = CIA) (cfs) (cf) (cf) (cf)
2 5.84 4.81 577.32 20.68 556.64
4 3.72 3.07 735.83 41.36 694.47
6 2.86 2.36 848.03 62.04 785.99
8 2.37 1.95 937.86 82.71 855.15
10 2.05 1.69 1014.04 103.39 910.65
12 1.82 1.50 1080.86 124.07 956.79
14 1.65 1.36 1140.78 144.75 996.03
16 1.51 1.25 1195.36 165.43 1029.93
18 1.40 1.15 1245.67 186.11 1059.56
20 1.31 1.08 1292.46 206.79 1085.67
24 1.16 0.96 1377.62 248.14 1129.48
26 1.10 0.91 1416.76 268.82 1147.94
28 1.05 0.87 1453.99 289.50 1164.49
30 1.00 0.83 1489.53 310.18 1179.35
32 0.96 0.79 1523.56 330.86 1192.70
34 0.93 0.76 1556.23 351.54 1204.69
36 0.89 0.74 1587.68 372.22 1215.46
38 0.86 0.71 1618.01 392.90 1225.11
40 0.83 0.69 1647.32 413.57 1233.74
42 0.81 0.66 1675.69 434.25 1241.44
44 0.78 0.65 1703.20 454.93 1248.27
46 0.76 0.63 1729.90 475.61 1254.29
48 0.74 0.61 1755.87 496.29 1259.58
50 0.72 0.59 1781.13 516.97 1264.16
52 0.70 0.58 1805.75 537.65 1268.10
54 0.69 0.56 1829.76 558.33 1271.44
56 0.67 0.55 1853.20 579.00 1274.20
58 0.65 0.54 1876.10 599.68 1276.42
60 0.64 0.53 1898.50 620.36 1278.13
62 0.63 0.52 1920.41 641.04 1279.37
64 0.61 0.51 1941.87 661.72 1280.15
66 0.60 0.50 1962.90 682.40 1280.50 Required Storage
68 0.59 0.49 1983.51 703.08 1280.44
70 0.58 0.48 2003.74 723.76 1279.98
72 0.57 0.47 2023.59 744.43 1279.16
74 0.56 0.46 2043.09 765.11 1277.98
76 0.55 0.45 2062.25 785.79 1276.46
78 0.54 0.44 2081.09 806.47 1274.62
80 0.53 0.44 2099.61 827.15 1272.46
82 0.52 0.43 2117.83 847.83 1270.00
84 0.51 0.42 2135.77 868.51 1267.26
86 0.51 0.42 2153.43 889.19 1264.25
88 0.50 0.41 2170.83 909.86 1260.97
90 0.49 0.41 2187.97 930.54 1257.43
92 0.48 0.40 2204.87 951.22 1253.65
94 0.48 0.39 2221.53 971.90 1249.63
96 0.47 0.39 2237.96 992.58 1245.38
98 0.47 0.38 2254.17 1013.26 1240.91
100 0.46 0.38 2270.16 1033.94 1236.23
102 0.45 0.37 2285.95 1054.61 1231.34
104 0.45 0.37 2301.54 1075.29 1226.25
106 0.44 0.36 2316.93 1095.97 1220.96
108 0.44 0.36 2332.14 1116.65 1215.49
110 0.43 0.36 2347.17 1137.33 1209.84
112 0.43 0.35 2362.02 1158.01 1204.01
114 0.42 0.35 2376.69 1178.69 1198.01
116 0.42 0.34 2391.21 1199.37 1191.84
118 0.41 0.34 2405.56 1220.04 1185.51
120 0.41 0.34 2419.75 1240.72 1179.02
Notes