HomeMy WebLinkAboutST1 - Valley Glass Stormwater Design Report
723-00 Valley Glass and Windows - Stormwater Design Report Page 1
February 2025
TABLE OF CONTENTS
Overview ......................................................................................................................................... 2
Existing Conditions ........................................................................................................................... 2
Stormwater Design Criteria ............................................................................................................. 3
Proposed Stormwater Improvements ............................................................................................. 3
APPENDIX
Appendix A ...................................................................................................... Drainage Basin Maps
Appendix B ............................................................................................. Drainage Basin Calculations
Appendix C ................................................................................................ Groundwater Monitoring
Appendix D .................................................... Stormwater Facilities Operation & Maintenance Plan
723-00 Valley Glass and Windows - Stormwater Design Report Page 2
February 2025
OVERVIEW
The purpose of this report is to detail the stormwater management design for proposed site
improvements for Valley Glass and Windows, located on Lot 3 of Tract 6 Plus Vacated Single Tree Court,
Gardner Simmental Plaza Subdivision. The lot is located in Section 35, Township 01 South, Range 5 East,
City of Bozeman, Gallatin County, Montana. The property is located on the southwest corner of Rawhide
Ridge Road and Simmental Way. The property currently has an approximately 12,000 square foot
warehouse and office building, along with an associated parking lot located to the north and south of the
building.
The proposed development on the property includes an 11,800 square foot warehouse building on the
western side of the lot. The existing parking lot will also be expanded along the front of the proposed
building, as well as east of the existing building. The street frontages along Simmental Way and Rawhide
Ridge Road will be improved to City standards with pavement widening and curb and gutter. Stormwater
runoff from the site and street improvements will be managed with on-site systems.
EXISTING CONDITIONS
Overall, the existing site grades from south to north at 1-1.5%. The existing parking lot on the north side
of the existing building slopes at approximately 2% to existing stormwater ponds located north of the
parking lot. The parking lot along the south side of the building grades to the southeast to an existing pond
located in a landscaped are near the property line and to the west toward the undeveloped portion of the
lot. The eastern portion of the property is currently a large landscaped area that generally grades to the
north. The western portion of the lot is currently a gravel parking and materials lay-down area. A concrete
truck ramp in the northwest corner of the existing building drains to an existing drywell in the ramp. The
existing site improvements were permitted and approved through the City of Bozeman site plan process
in the 1990’s. Appendix A includes a pre-development drainage basin map that details the existing
drainage patterns on the property.
The adjacent right-of-ways of Rawhide Ridge Road and Simmental Way are currently uncurbed and more
closely resemble a county road section with roadside swales than a city street section. Runoff from the
paved streets and much of the project site currently drains to these roadside swales for infiltration. The
roadside swales along the property frontage ultimately flow west along the south side of Rawhide Ridge
Road.
The runoff generated by the existing site was estimated using the modified rational method outlined in
the COB DSSP with the 10-year 2-hour design storm. The property and associated right-of-way were
assigned runoff coefficients based on the cover type. The existing site was broken into 4 pre-development
drainage basins based on current site conditions. Three of these drainage basins convey runoff to existing
stormwater facilities on site while the rest of the site (Drainage Basin 1) drains to the previously discussed
roadside swale on Rawhide Ridge Road. The pre-development off-site runoff flow rate in Drainage Basin
1 during the 25-yr design storm for conveyance facilities was estimated to be 1.79 cfs, while the runoff
volume during the 10-yr, 2-hr design storm was estimated to be 3,616 cf.
Groundwater monitoring of the existing site was performed during the spring of 2024 by IMEG Corp. Two
perforated PVC pipes were installed as monitoring wells, one on the northwest side and one on the
723-00 Valley Glass and Windows - Stormwater Design Report Page 3
February 2025
northeast side of the property. The wells were monitored approximately during seasonal high
groundwater (April – June). High groundwater was found at 3.55’ below ground surface (bgs) on the
western well and at 6.00’ bgs on the eastern well. These peak groundwater elevations were used to create
an estimated seasonal high groundwater surface across the site for use in designing the proposed
stormwater systems. It was estimated that seasonal high groundwater generally follows the slope of the
site from north to south at ~1.5%.
STORMWATER DESIGN CRITERIA
The proposed stormwater improvements for the Valley Glass and Windows Site Plan are designed to meet
the City of Bozeman Design Standards and Specifications Policy (2004 – w/ addendums approved through
03/13/20). The design storm return interval for retention and detention facilities in the City of Bozeman
is 10-years. The storm duration for these design events is 2-hours. Conveyance facilities are required to
have sufficient capacity to convey a 25-year storm event. Time of Concentration for the design storms
were calculated using the Manning Equation for channelized flow and the equation for sheet flow from
Section II.E.6. of the COB DSSP. The Montana Post-Construction Storm Water BMP Design Guidance
Manual recommends 3 feet of separation between seasonal high groundwater levels and stormwater
retention/detention facilities. Given the high levels of groundwater on the property and the fact that
much of this stormwater design includes retrofitting existing site improvements to meet current
stormwater standards, following this recommendation is not feasible. However, the stormwater facilities
have been designed to above the seasonal high groundwater table.
Multiple drainage basins on site will sheet flow runoff to their respective drainage systems without
entering conveyance facilities such as curbs, pipes, or chases. For these drainage basins with no
conveyance facilities, no conveyance capacity calculations for the 25-year storm event have been
provided. Instead, runoff volume calculations for the 10-year design storm have been calculated.
It should also be noted that the City of Bozeman DSSP requires retention of runoff from the first 0.5” of
rainfall from impervious areas. However, since all proposed storage systems on site are retention facilities,
not detention, all runoff from the design storm event will be retained. Therefore, since the design storm
requires retention of .82” of water, retention calculations for the first 0.5” of rainfall are not necessary.
PROPOSED STORMWATER IMPROVEMENTS
With the proposed site improvements, the city Engineering Department is requiring that the entire
property be brought into compliance with city stormwater standards. Therefore, wherever possible,
runoff generated by the existing and proposed improvements on the lot will be retained on-site using a
combination of retention ponds and underground infiltration systems. Runoff will be conveyed to these
systems via downspouts, curb and gutter, and curb chases. Since the proposed site improvements will
result in limited landscaped area for surface storage, ADS Stormtech underground retention systems were
chosen for the majority of the proposed systems for ease of construction and maintenance. The systems
are detailed within the site plan set.
Since the existing site improvements and stormwater facilities were permitted by the city with the original
site design for the property, in an effort to minimize disturbance to the existing site, several existing storm
facilities that are not being impacted by the proposed site improvements will remain in their existing
location or condition.
723-00 Valley Glass and Windows - Stormwater Design Report Page 4
February 2025
One example of this is the existing dry well in the existing loading dock. We do not have record drawings
or an accurate means of determining the capacity of the existing dry well. However, since the existing
loading dock was permitted through the city and no improvements are proposed to the loading dock, the
existing dry well will remain in use. This dry well only receives runoff from the limited area of the loading
dock, and since it is below the surrounding parking lot grades and building finish floor elevations, even if
it were to fail it would not present a flooding hazard to any surrounding facilities.
Similarly, the existing retention pond (Pond C) on the south side of the existing building drains a portion
of the existing parking lot and building roof and was permitted with the original site improvements. This
portion of the existing parking lot is not proposed to be altered with the site improvements. Therefore,
even though the existing pond is surrounded by existing underground utilities and does not meet current
city utility setbacks, the pond is proposed to remain in use. The pond will be re-graded to meet city
requirements for water storage depth and side slopes, but will largely remain in its current location.
RIGHT-OF-WAY RUNOFF
As mentioned previously, the city is requiring that the adjacent street frontages be improved with curb
and gutter with the proposed site improvements. The city concept review comments require runoff from
these adjacent improvements to be captured and treated on site. However, the property to the south of
the project site recently improved their frontage of Simmental Way with curb and gutter as well, but did
not provide any stormwater retention for their street frontage on their property. Since runoff from this
southern property flows into the proposed Simmental gutter for this project, runoff from that property
will now need to be captured on the project site.
Therefore, city staff indicated that this project will only need to capture and treat runoff from a section of
right of way that is similar to the length of the project frontage on Simmental and Rawhide Ridge, but not
necessarily the actual property’s frontage right-of-way. In order to address this, the proposed stormwater
improvements capture runoff from the Simmental right-of-way for the frontage of the property to the
south of the project site and the project site’s frontage as well as the eastern portion of the project’s
Rawhide Ridge frontage. The western portion of the Rawhide Ridge frontage will flow west and discharge
into the roadside ditch west of the project site. Pre-development runoff calculations have been provided
in Appendix B and on the Drainage Basin Maps in Appendix A to show that the post-development
discharge into the Rawhide Ridge roadside ditch is significantly lower than the pre-development discharge
at this location.
DRAINAGE BASIN SUMMARIES
The site was broken in to 12 drainage basins with some sub basins for conveyance analysis. Calculations
for the drainage basins and facilities are included in Appendix B.
Drainage Basin #1 is located northwest of the existing building and northeast of the proposed building.
This basin receives runoff from the parking lot between the two buildings and drains via a valley gutter to
Stormtech System A, which is a SC160 LP model stormtech system.
Drainage Basin #2 includes the western roof of the existing building and the southwestern portion of the
parking lot. Runoff from this area is conveyed via sheet flow to a short valley gutter in the parking lot
which drains into Stormtech System B. this system is a SC160 LP model stormtech system.
723-00 Valley Glass and Windows - Stormwater Design Report Page 5
February 2025
Drainage Basin #3 is an existing drainage basin that includes the central portion of the existing building’s
roof as well as the south-central portion of the parking lot. This area drains to an existing retention pond
on the south side of the parking lot (Pond C) that will be regraded to a 1’ water storage depth and 4:1 side
slopes.
Drainage Basin #4 includes the eastern portion of the existing buildings roof and the new eastern parking
lot. This area will sheet flow to a valley gutter that drains to Stormtech System C, which is a SC310 model
stormtech system.
Drainage Basin #5 includes the northern portion of the existing parking lot. This area currently drains to
two ponds in the landscaped area along Rawhide Ridge Road. However, these existing ponds are located
in the area that will be dedicated at a 10’ public utility easement, so the ponds will need to be shifted
south. In order to meet the design storage volume and fit the ponds within the remaining landscaped area
outside the utility easement, dry wells with perforated pipe will be installed beneath the new pond to
increase storage volume.
Drainage Basin #6 includes the western portion of the Rawhide Ridge Road right-of-way that will discharge
off site to the west. Runoff from this area will be conveyed to a new curb along the south side of the street
section that will convey runoff to the roadside ditch to the west. Runoff generated by this Drainage Basin
in the post-development condition will be 713 cf, which is 2,903 cf less than the 3,616 cf of runoff that is
estimated to be discharged to this location in the current, pre-development site condition.
Drainage Basin #7 includes the western half of the Simmental Way right-of-way from Boot Hill Court to
the intersection of Rawhide Ridge Road. Runoff from this area will be conveyed via new curb and gutter
to a storm chase just south of the intersection with Rawhide Ridge Road which discharges into a new
retention pond (Pond A). Since this storm chase is on-grade instead of at a low point there is a chance that
sedimentation or snow/ice may lead to runoff bypassing the chase. Therefore, a second chase is proposed
downgradient of this chase on Rawhide Ridge Road to ensure that runoff does not bypass this system and
flow off-site to Drainage Basin 6.
Drainage Basin #8 includes the northern portion of the proposed building’s roof as well as the proposed
loading dock and adjacent landscaped area. The roof (DB #8A) will drain via roof downspouts to an 8”
storm line along the west side of the building and on to Stormtech System D (SC160 LP Model). The loading
dock (DB #8B) will drain to a catch basin at the low end of the dock and on to this same stormtech system.
The western manhole of the stormtech sytem will have a slotted grate to capture runoff from the
landscaped area adjacent to the dock (DB #8C).
Drainage Basin #9 includes the southern portion of the proposed building’s roof. Similar to DB #8A, roof
runoff will drain via roof downspouts to an 8” storm line that conveys runoff to Stormtech System E (SC310
model) located on the south side of the existing building. This Stormtech system will only receive runoff
from the roof in DB #9.
Drainage Basin #10 includes a 20’ wide rock storage pad on the south side of the proposed building and
an adjacent landscape strip along the property line. Since Stormtech System E is located under this rock
pad, there is not room to install an additional drainage feature in this drainage basin. Runoff from this
area will not be directed to Stormtech System E because sediment from the rock pad may inundate the
stormtech system over time. Instead, the rock pad and adjacent landscaped area is graded to a low point
723-00 Valley Glass and Windows - Stormwater Design Report Page 6
February 2025
on the south side of the pad so any runoff in this drainage basin will pond here. The storage volume of the
low point has been calculated to be 413 cf, which is 3x larger than the runoff volume of 123 cf that would
be generated by the 10-yr design storm.
Drainage Basin #11 includes the existing loading dock. As discussed previously, this loading dock drains to
an existing dry well that has an unknown storage volume. However, this loading dock and dry well were
permitted through the City of Bozeman site plan process with the original site improvements, so the dry
well is proposed to remain in its current condition. This loading dock does not receive runoff from any
other portions of the site, so although the storage capacity of the dry well is unknown, it is not expected
to receive enough runoff to cause flooding or safety issues.
Drainage Basin #12 includes the 5’ wide landscaped area along the western property line that will sheet
flow off-site to the west. This area is estimated to generate a negligible 12 cf of runoff during the 10-year
storm event. When combined with the 713 cf of runoff from DB#6, the total off-site runoff from the
project site will be 725 cf to the west, which is 2,891 cf less than the pre-development runoff volume of
3,616 that is currently estimated to discharge to this area.
Pre-Development Runoff Summary (10-yr 2-hr storm)
Drainage Basin Area (Ac.)
Composite C-
Value Q (10-yr) Facility
1 2.23 0.55 1.46 Off Site
2 0.33 0.79 0.11 Existing Ponds
3 0.20 0.76 0.06 Existing Pond
4 0.04 0.95 0.02 Existing Dry Well
Post-Development Runoff Summary (10-yr 2-hr storm)
Drainage Basin Area (Ac.)
Composite C-
Value Q (10-yr) Vreq (ft3)Vpro (ft3) Facility
1 0.20 0.90 0.07 526 605 Stormtech System A
2 0.42 0.90 0.16 1,123 1,180 Stormtech System B
3 0.18 0.81 0.06 421 432 Pond C
4 0.49 0.73 0.15 1,066 1,200 Stormtech System C
5 0.34 0.79 0.11 795 804 Pond B & Dry Wells
6 0.30 0.82 0.10 713 N/A Off Site
7 0.73 0.59 0.17 1260 1404 Pond A
8 0.22 0.77 0.07 502 514 Stormtech System D
9 0.18 0.95 0.07 515 540 Stormtech System E
10 0.06 0.66 0.02 123 415 Swale A
11 0.04 0.95 0.02 110 Unknown Existing Dry Well
12 0.02 0.20 0.00 12 N/A Off Site
Pre vs Post Development Runoff
Condition Runoff Volume
(10-yr) (ft3)
Runoff Flow Rate
(25-yr) (cfs)
Pre-Development 3,616 1.79
Post-Development 725 0.88
777
440
110
Runoff Volume (V) (ft3)
3,616
Appendix A
Drainage Basin Maps
CO
EXISTINGDB #4SIMMENTAL WAYRAWHIDE RIDGE ROAD
EXISTING
DB #2
EXISTING
DB #1
EXISTING
DB #1
EXISTING
DB #3
EXISTING BUILDING
RETENTION SWALE #5
REQ. VOL.:132 CF
PRO. VOL.:390 CF
EXISTING RETENTION POND
ESTIMATED VOL.:714 CF
EXISTING RETENTION PONDS
ESTIMATED VOL.:489 CF
EXISTING LOADING DOCK DRY WELL
VOLUME UNKNOWN
DISCHARGE PONT FOR PRE-DEVELOPMENT OFF-SITE RUNOFF
FACILITY: RAWHIDE RIDGE ROADSIDE DITCH
ESTIMATED RUNOFF VOLUME: 3,107 CF
EXISTING DB #1 TIME OF CONCENTRATION PATH
EXISTING PARKING LOT
EXISTING PARKING LOT
EXISTING LAWN
EXISTING GRAVEL
STORAGE AREA
PROJECT NO:
DATE:
ENGINEER:
REVISIONS
DATENO.DESC.
723-01
February 13, 2025
AK
DB 1
20'0 40'
SCALE 1" = 20'
N
LEGEND
DRAINAGE BASIN BOUNDARY
DRAINAGE BASIN COVER TYPE - ROOF
STORM CATCH BASIN
STORM POND / SWALE
SYMBOL DESCRIPTION
DRAINAGE BASIN COVER TYPE - IMPERVIOUS
SHEET OF 21VALLEY GLASS AND WINDOWDRAINAGE BASIN MAP - PRE-DEVELOPMENTBOZEMAN, MONTANATIME OF CONCENTRATION PATH
DRAINAGE DIRECTION
DRAINAGE BASIN COVER TYPE - PERVIOUS
DRAINAGE BASIN COVER TYPE - GRAVEL
CO
NO PARKINGNO PARKINGCO
NO PARKINGNO PARKINGSTSTSTST
STSTSTSTGASST15''ST 15''STSTST
ST
ST
ST
ST
ST
CO
SEE INSET ABOVE FOR DRAINAGEBASIN #7 OVER VIEWSIMMENTAL WAYRAWHIDE RIDGE ROAD
W
W
DB #12
DRAIN BASIN E
ST MANHOLE E
INLINE DRAIN E
INLINE DRAIN D
ST MANHOLE C
ST MANHOLE B
DRAIN BASIN D-1 DRAIN BASIN D-4
ST INLET A ST MANHOLE 1-2 ST MANHOLE 1-3ST MANHOLE 1-1DRAIN BASIN D-2
DRAIN BASIN D-3
ST MANHOLE D
DB #1
DB #3
DB #4
DB #2
DB #9
DB #10
DB #11
DB #5
DB #8 DB #8B
DB #8C
DB #8A
GROUNDWATER
MONITORING
WELL #2
GROUNDWATER
MONITORING
WELL #1
RETENTION SWALE
REQ. VOL.:123 CF
PRO. VOL.:415 CF
CURB CHASE #2
POND B & DRY WELLS
REQ. VOLUME: 795 CF
PRO. VOLUME: 804 CF
BOTTOM OF SYSTEM STONE ELEV: 4704.67
EST. SHGW ELEV: 4704.60
STORMTECH - SYSTEM A
SC160 LP CHAMBERS
REQ. VOLUME: 526 CF
PRO. VOLUME: 605 CF
BOTTOM OF SYSTEM STONE ELEV: 4705.00
EST. SHGW ELEV: 4704.90
STORMTECH - SYSTEM D
SC160 LP CHAMBERS
REQ. VOLUME: 502 CF
PRO. VOLUME: 514 CF
BOTTOM OF SYSTEM STONE ELEV: 4704.50
EST. SHGW ELEV: 4704.50
STORMTECH - SYSTEM E
SC310 CHAMBERS
REQ. VOLUME: 515 CF
PRO. VOLUME: 540 CF
BOTTOM OF SYSTEM STONE ELEV: 4706.50
EST. SHGW ELEV: 4706.50
STORMTECH - SYSTEM B
SC160 LP CHAMBERS
REQ. VOLUME: 1123 CF
PRO. VOLUME: 1180 CF
BOTTOM OF SYSTEM STONE ELEV: 4706.30
EST. SHGW ELEV: 4706.15
STORMTECH - SYSTEM C
SC310 CHAMBERS
REQ. VOLUME: 1066 CF
PRO. VOLUME: 1200 CF
BOTTOM OF SYSTEM STONE ELEV: 4706.25
EST. SHGW ELEV: 4706.15
POND A
1.5' WATER STORAGE DEPTH
4:1 SIDE SLOPES
REQ. VOLUME: 1260 CF
PRO. VOLUME: 1404 CF
BOTTOM OF POND ELEV: 4708.30
EST. SHGW ELEV: 4704.80
POND C
1' WATER STORAGE DEPTH
4:1 SIDE SLOPES
REQ. VOLUME: 421 CF
PRO. VOLUME: 432 CF
BOTTOM OF POND ELEV: 4710.00
EST. SHGW ELEV: 4706.60
OFFSITE DISCHARGE (DB #6 & DB #12)
PRE-DEV RUNOFF VOL (10-YR STORM): 3,107 CF
POST-DEV RUNOFF VOL (10-YR STORM): 725 CF
PRE-DEV RUNOFF RATE (25-YR STORM): 1.79 CFS
POST-DEV RUNOFF RATE (25-YR STORM): 0.88 CFS
-1.2%DB #7A
DB #7B
DB #7C
CURB CHASE #1
DB #7
-0.8%
PIPE D-1
PIPE D
PIPE D-3
DB #6
4712
4711 471247114711471147114711
4710
4709
4712
4709
4710
4711
4711
4712
47
1
3
4714
47144713471
2
47114710
4711
47124710
4710
471147104709
471047104710470947084708
4708
4709
4710
47114711 4710471147114710
PIPE E WSIMMENTAL WAYBOOT HILL COURTST MANHOLE C
DB #4
DB #7A
DB #7B
DB #7C
DB #7
CURB CHASE #1
SIMMENTAL WAY ℄
PROJECT NO:
DATE:
ENGINEER:
REVISIONS
DATENO.DESC.
723-01
February 13, 2025
AK
DB 2
20'0 40'
SCALE 1" = 20'
N
LEGEND
DRAINAGE BASIN BOUNDARY
DRAINAGE BASIN COVER TYPE - PERVIOUS
STORM MANHOLE
STORM INLET
STORM CATCH BASIN
STORM POND / SWALE
SYMBOL DESCRIPTION
ST
DRAINAGE BASIN COVER TYPE - IMPERVIOUS
DRAINAGE BASIN COVER TYPE - ROOF
SHEET OF 22VALLEY GLASS AND WINDOWDRAINAGE BASIN MAP - POST DEVELOPMENTBOZEMAN, MONTANATIME OF CONCENTRATION PATH
DRAINAGE DIRECTION
0 40'80'
SCALE 1" = 40'NEXISTING LOADING DOCK DRYWELL
VOLUME UNKNOWN
SUB DRAINAGE BASIN BOUNDARY
DRAINAGE BASIN COVER TYPE - GRAVEL
Appendix B
Drainage Basin Calculations
Existing Drainage Basin 1
Land Use Drainage Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 1 26,773 0.61 0.95 0.5839
DB - Pervious 1 50,460 1.16 0.20 0.2317
DB - Gravel 1 11,557 0.27 0.85 0.2255
DB - Roof 1 8,427 0.19 0.95 0.1838
Total 97,217 2.23 1.2249
Weighted C:0.55
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.59
C * Cf 0.59 0.65 0.74
D - Length of Basin (ft) 35
Sb - Slope of Basin (%)2.0000
To - Time of Conc. - Overland (min.)4.48 3.96 3.18
L - Length of Channel (ft) 655
n - Manning's Coefficient 0.15
R - Hydraulic Radius(ft) 0.50
Sc - Slope of Channel (ft/ft)0.009
V - Velocity (ft/sec) 0.59 0.59 0.59
Tc - Time of Conc. - Channel (min.)18.5 18.5 18.5
Time of Concentration (Ttotal)22.98 22.46 21.68
X - Storm Duration (hr) 0.38 0.37 0.36
I - Intensity (in/hr)1.19 1.46 2.00
Q - Peak Runoff (cfs) 1.46 1.79 2.45
Total Area (Acres) = 2.23
Weighted C = 0.55
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.50
Pre-Development Runoff Volume (ft3)=3,616
Rainfall Frequency (yr)
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: Ponds
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 2 10,653 0.24 0.95 0.232
DB - Roof 2 764 0.02 0.95 0.017
DB - Pervious 2 3,064 0.07 0.20 0.014
Totals 14,481 0.33 0.2631
Weighted C:0.79
Total Area (Acres) = 0.33
Weighted C = 0.79
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.11
Runoff Volume (ft3)=777
Generated Runoff Volume - 10 year, 2 hour Storm
Storage Facility Calculations
Existing DB # 2
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: Pond
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 3 3,208 0.07 0.95 0.070
DB - Roof 3 3,183 0.07 0.95 0.069
DB - Pervious 3 2,126 0.05 0.20 0.010
Totals 8,518 0.20 0.1491
Weighted C:0.76
Total Area (Acres) = 0.20
Weighted C = 0.76
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.06
Runoff Volume (ft3)=440
Generated Runoff Volume - 10 year, 2 hour Storm
Storage Facility Calculations
Existing DB # 3
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Dry Well
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 4 1,713 0.04 0.95 0.037
DB - Roof 4 0 0.00 0.95 0.000
DB - Pervious 4 0 0.00 0.20 0.000
Totals 1,713 0.04 0.0374
Weighted C:0.95
Total Area (Acres) = 0.04
Weighted C = 0.95
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.02
Runoff Volume (ft3)=110
Generated Runoff Volume - 10 year, 2 hour Storm
Storage Facility Calculations
Existing DB # 4
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Basis for Calculations
Time of Concentration (Ttotal) (minutes) Rainfall Intensity (I) (in/hr)
Ttotal = To + Tc Rainfall Frequency Equation
To = Time of Concentration for Overland Flow 10 year I = 0.64(X-.65)
Tc = Time of Concentration for Channel Flow 25 year I = 0.78(X-.64)
Whereas:100 year I = 1.01(X-.67)
To = 1.87 (1.1-CCf)D1/2 Tc = L/V/60 Whereas:
(Sb)1/3 X = Storm Duration (hr)
C = Runoff Coefficient L = Length of Channel (ft) = Ttotal / 60
Cf = Frequency Adjustment Factor V = Mean Velocity (ft/sec)
D = Length of Basin (ft)V = 1.486 Gutter Capacity
Sb = Slope of Basin (%) n Q = (1.486/n)AR2/3 S1/2
n = Manning's Coefficient
R = Hydraulic Radius (ft) Hydraulic Radius
= Area (ft2) / Wetted Perimeter (ft)Integral Curb & Gutter 0.136
Sc = Slope of Channel (ft/ft)
Rational Method Peak Runoff (Q)
Q = CIA
Pre-Development Runoff Summary (10-yr 2-hr storm)
Drainage Basin Area (Ac.)
Composite C-
Value Q (10-yr) Facility
1 2.23 0.55 1.46 Off Site
2 0.33 0.79 0.11 Existing Ponds
3 0.20 0.76 0.06 Existing Pond
4 0.04 0.95 0.02 Existing Dry Well
Post-Development Runoff Summary (10-yr 2-hr storm)
Drainage Basin Area (Ac.)
Composite C-
Value Q (10-yr)Vreq (ft3)Vpro (ft3)Facility
1 0.20 0.90 0.07 526 605 Stormtech System A
2 0.42 0.90 0.16 1,123 1,180 Stormtech System B
3 0.18 0.81 0.06 421 432 Pond C
4 0.49 0.73 0.15 1,066 1,200 Stormtech System C
5 0.34 0.79 0.11 795 804 Pond B & Dry Wells
6 0.30 0.82 0.10 713 N/A Off Site
7 0.73 0.59 0.17 1260 1404 Pond A
8 0.22 0.77 0.07 502 514 Stormtech System D
9 0.18 0.95 0.07 515 540 Stormtech System E
10 0.06 0.66 0.02 123 415 Swale A
11 0.04 0.95 0.02 110 Unknown Existing Dry Well
12 0.02 0.20 0.00 12 N/A Off Site
Pre vs Post Development Runoff
Condition Runoff Volume
(10-yr) (ft3)
Runoff Flow Rate
(25-yr) (cfs)
Pre-Development 3,616 1.79
Post-Development 725 0.88
777
440
110
R2/3(Sc)1/2
Drainage Basin Time of Concentration and Peak Runoff Calculations
Runoff Volume (V) (ft3)
3,616
Drainage Basin 1
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 1 8061 0.19 0.95 0.1758
DB - Pervious 1 528 0.01 0.20 0.0024
DB - Roof 1 0 0.00 0.95 0.0000
Total 8589 0.20 0.1782
Weighted C:0.90
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 67
Sb - Slope of Basin (%)1.0000
To - Time of Conc. - Overland (min.)2.3 0.84 -1.34
L - Length of Channel (ft) 47
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft)0.02
V - Velocity (ft/sec) 4.28 4.28 4.28
Tc - Time of Conc. - Channel (min.)0.18 0.18 0.18
Time of Concentration (Ttotal)555
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr) 3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.57 0.68 0.95
Gutter Capacity (0.15' Freeboard)
n - Manning's Coefficient 0.013
A - Area (ft2)1.25
R - Hydraulic Radius(ft)0.136
Sc - Slope of Channel (ft/ft)0.02
Gutter Capacity (cfs) 5.34
Rainfall Frequency (yr)
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Stormtech
C = Runoff Coefficient Facility Make/Model: SC-160LP
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 1 8,061 0.19 0.95 0.176
DB - Roof 1 0 0.00 0.95 0.000
DB - Pervious 1 528 0.01 0.20 0.002
Totals 8,589 0.20 0.1782
Weighted C:0.90
Total Area (Acres) = 0.20
Weighted C = 0.90
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.07
Req. Runoff Volume (ft3)=526
Total Ret Volume (ft3)605
Provided Retention (STORMTECH)
Storage Facility Calculations
STORMTECH SYSTEM A
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Stormtech
C = Runoff Coefficient Facility Make/Model: SC-160LP
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 2 10,581 0.24 0.95 0.231
DB - Roof 2 6,606 0.15 0.95 0.144
DB - Pervious 2 1,235 0.03 0.20 0.006
Totals 18,422 0.42 0.3805
Weighted C:0.90
Total Area (Acres) = 0.42
Weighted C = 0.90
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.16
Req. Runoff Volume (ft3)=1,123
Total Ret Volume (ft3)1180
Provided Retention (STORMTECH)
Storage Facility Calculations
STORMTECH SYSTEM B
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Pond
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 3 3,041 0.07 0.95 0.066
DB - Roof 3 3,187 0.07 0.95 0.070
DB - Pervious 3 1,457 0.03 0.20 0.007
Totals 7,685 0.18 0.1425
Weighted C:0.81
Total Area (Acres) = 0.18
Weighted C = 0.81
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.06
Req. Runoff Volume (ft3)=421
Total Ret Volume (ft3)432
Provided Retention (Pond)
Storage Facility Calculations
POND C
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Stormtech
C = Runoff Coefficient Facility Make/Model: SC-310
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 4 13,447 0.31 0.95 0.293
DB - Roof 4 1,818 0.04 0.95 0.040
DB - Pervious 4 6,162 0.14 0.20 0.028
Totals 21,427 0.49 0.3612
Weighted C:0.73
Total Area (Acres) = 0.49
Weighted C = 0.73
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.15
Req. Runoff Volume (ft3)=1,066
Total Ret Volume (ft3)1200
Provided Retention (STORMTECH)
Storage Facility Calculations
STORMTECH SYSTEM C
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year):10 Storage Method: Retention
Rational Method Peak Runoff Equation:Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: Pond & Dry Wells
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr):0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 5 10,919 0.25 0.95 0.238
DB - Roof 5 765 0.02 0.95 0.017
DB - Pervious 5 3,189 0.07 0.20 0.015
Totals 14,873 0.34 0.2695
Weighted C:0.79
Total Area (Acres) = 0.34
Weighted C = 0.79
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.11
Req. Runoff Volume (ft3)=795
Drywell 1 - Inner Diameter (ft) 3
Depth (ft) 3
Volume of Drywel 1 (ft3)21.2
Drywell 2 - Inner Diameter (ft) 3
Depth (ft) 3
Volume of Drywell 2 (ft3)21.2
Drywell 3 - Inner Diameter (ft) 3
Depth (ft) 3
Volume of Drywell 3 (ft3)21.2
Lateral Pipe Diameter (inches) 15
Lateral Length (ft) 85
Volume of Lateral (ft3)104.3
Washed Rock Porosity 40%
Lateral Washed Rock Width (inches) 72
Lateral Washed Rock Height (inches) 24
Volume of Washed Rock Around Lateral (ft3)366.3
Volume Pond (ft3)270.0
Total System Ret Volume (ft3)804.2
Provided Retention (Pond & Drywells w/ Perf Pipe)
Storage Facility Calculations
POND B & DRY WELLS
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 6
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 6 10602 0.24 0.95 0.2312
DB - Pervious 6 2271 0.05 0.20 0.0104
DB - Roof 6 0 0.00 0.95 0.0000
Total 12873 0.30 0.2416
Weighted C:0.82
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.5
C * Cf 0.5 0.55 0.63
D - Length of Basin (ft) 16
Sb - Slope of Basin (%)2.00
To - Time of Conc. - Overland (min.)3.56 3.27 2.82
L - Length of Channel (ft) 376
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft)0.008
V - Velocity (ft/sec) 2.7 2.7 2.7
Tc - Time of Conc. - Channel (min.) 2.32 2.32 2.32
Time of Concentration (Ttotal)5.88 5.59 5.14
X - Storm Duration (hr) 0.10 0.09 0.09
I - Intensity (in/hr) 2.90 3.56 5.24
Q - Peak Runoff (cfs) 0.7 0.86 1.27
Gutter Capacity (0.15' Freeboard)
n - Manning's Coefficient 0.013
A - Area (ft2)1.25
R - Hydraulic Radius(ft)0.136
Sc - Slope of Channel (ft/ft)0.008
Gutter Capacity (cfs) 3.38
Rainfall Frequency (yr)
Design Rainfall Frequency (year): 10 Storage Method: N/A
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: N/A
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 6 10,602 0.24 0.95 0.231
DB - Roof 6 0 0.00 0.95 0.000
DB - Pervious 6 2,271 0.05 0.20 0.010
Totals 12,873 0.30 0.2416
Weighted C:0.82
Total Area (Acres) = 0.30
Weighted C = 0.82
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.10
Req. Runoff Volume (ft3)=713
Total Ret Volume (ft3)N/A
Provided Retention
Storage Facility Calculations
Off Site
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 7A
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 7A 13422 0.31 0.95 0.2927
DB - Pervious 7A 10973 0.25 0.20 0.0504
DB - Roof 7A 0 0.00 0.95 0.0000
Total 24394 0.56 0.3431
Weighted C:0.61
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.37
C * Cf 0.37 0.41 0.46
D - Length of Basin (ft) 31
Sb - Slope of Basin (%)2.00
To - Time of Conc. - Overland (min.)6.03 5.73 5.27
L - Length of Channel (ft) 610
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.012
V - Velocity (ft/sec) 3.31 3.31 3.31
Tc - Time of Conc. - Channel (min.)3.07 3.07 3.07
Time of Concentration (Ttotal)9.1 8.8 8.34
X - Storm Duration (hr) 0.15 0.15 0.14
I - Intensity (in/hr) 2.18 2.66 3.79
Q - Peak Runoff (cfs) 0.75 0.91 1.3
Gutter Capacity (0.15' Freeboard)
n - Manning's Coefficient 0.013
A - Area (ft2)1.25
R - Hydraulic Radius(ft)0.136
Sc - Slope of Channel (ft/ft)0.012
Gutter Capacity (cfs) 4.14
Channel Chase
Width (in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity
(cfs)
Required
Capacity
(cfs)
12" Curb Cut 12 6 0.015 0.012 3.01 0.91
Rainfall Frequency (yr)
Curb Chase Capacity
Drainage Basin 7B
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 7B 2718 0.06 0.95 0.0593
DB - Pervious 7B 793 0.02 0.20 0.0036
DB - Roof 7B 0 0.00 0.95 0.0000
Total 3511 0.08 0.0629
Weighted C:0.78
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 25
Sb - Slope of Basin (%)3.00
To - Time of Conc. - Overland (min.)0.97 0.36 -0.57
L - Length of Channel (ft) 94
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.015
V - Velocity (ft/sec) 3.7 3.7 3.7
Tc - Time of Conc. - Channel (min.)0.42 0.42 0.42
Time of Concentration (Ttotal)555
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr) 3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.2 0.24 0.34
Gutter Capacity (0.15' Freeboard)
n - Manning's Coefficient 0.013
A - Area (ft2)1.25
R - Hydraulic Radius(ft)0.136
Sc - Slope of Channel (ft/ft)0.015
Gutter Capacity (cfs) 4.63
Channel Chase
Width (in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity
(cfs)
Required
Capacity
(cfs)
12" Curb Cut 12 6 0.010 0.012 2.46 0.24
Rainfall Frequency (yr)
Curb Chase Capacity
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Pond
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 7A 13,422 0.31 0.95 0.293
DB - Roof 7A 0 0.00 0.95 0.000
DB - Pervious 7A 10,973 0.25 0.20 0.050
DB - Impervious 7B 2,718 0.06 0.95 0.059
DB - Roof 7B 0 0.00 0.95 0.000
DB - Pervious 7B 793 0.02 0.20 0.004
DB - Impervious 7C 189 0.00 0.95 0.004
DB - Roof 7C 0 0.00 0.95 0.000
DB - Pervious 7C 3,629 0.08 0.20 0.017
Totals 31,723 0.73 0.4268
Weighted C:0.59
Total Area (Acres) = 0.73
Weighted C = 0.59
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.17
Req. Runoff Volume (ft3)=1,260
Total Runoff Volume (ft3)1404
Pre-Development Runoff Volume
Storage Facility Calculations
POND A
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 8A
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 8A 0 0.00 0.95 0.0000
DB - Pervious 8A 0 0.00 0.20 0.0000
DB - Roof 8A 3800 0.09 0.95 0.0829
Total 3800 0.09 0.0829
Weighted C:0.95
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 80
Sb - Slope of Basin (%)5.00
To - Time of Conc. - Overland (min.)1.47 0.54 -0.86
L - Length of Channel (ft) 0
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.01
V - Velocity (ft/sec) 3.02 3.02 3.02
Tc - Time of Conc. - Channel (min.)00 0
Time of Concentration (Ttotal)55 5
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr)3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.27 0.32 0.44
Pipe Pipe Size
(in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity (cfs)
Required
Capacity (cfs)
PIPE D-1 8 6.00 0.008 0.012 1.07 0.32
Rainfall Frequency (yr)
Pipe Capacity
Drainage Basin 8B
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 8B 3522 0.08 0.95 0.0768
DB - Pervious 8B 0 0.00 0.20 0.0000
DB - Roof 8B 0 0.00 0.95 0.0000
Total 3522 0.08 0.0768
Weighted C:0.95
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 85
Sb - Slope of Basin (%)2.50
To - Time of Conc. - Overland (min.)1.91 0.7 -1.11
L - Length of Channel (ft) 0
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.01
V - Velocity (ft/sec) 3.02 3.02 3.02
Tc - Time of Conc. - Channel (min.)00 0
Time of Concentration (Ttotal)55 5
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr)3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.25 0.29 0.41
Pipe Pipe Size
(in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity (cfs)
Required
Capacity (cfs)
Pipe D 6 4.50 0.008 0.012 0.50 0.29
Pipe Pipe Size
(in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity (cfs)
Required
Capacity (cfs)
Pipe D-2 8 6.00 0.0058 0.012 0.91 0.61
Rainfall Frequency (yr)
Pipe Capacity
Pipe Capacity
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Stormtech
C = Runoff Coefficient Facility Make/Model: SC-160LP
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 8A 0 0.00 0.95 0.000
DB - Roof 8A 3,800 0.09 0.95 0.083
DB - Pervious 8A 0 0.00 0.20 0.000
DB - Impervious 8B 3,522 0.08 0.95 0.077
DB - Roof 8B 0 0.00 0.95 0.000
DB - Pervious 8B 0 0.00 0.20 0.000
DB - Impervious 8C 0 0.00 0.95 0.000
DB - Roof 8C 0 0.00 0.95 0.000
DB - Pervious 8C 2,292 0.05 0.20 0.011
Totals 9,614 0.22 0.1702
Weighted C:0.77
Total Area (Acres) = 0.22
Weighted C = 0.77
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.07
Req. Runoff Volume (ft3)=502
Total Ret Volume (ft3)514
Provided Retention (STORMTECH)
Storage Facility Calculations
STORMTECH SYSTEM D
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 9
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 9 0 0.00 0.95 0.0000
DB - Pervious 9 0 0.00 0.20 0.0000
DB - Roof 9 8000 0.18 0.95 0.1745
Total 8000 0.18 0.1745
Weighted C:0.95
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 80
Sb - Slope of Basin (%)5.00
To - Time of Conc. - Overland (min.)1.47 0.54 -0.86
L - Length of Channel (ft) 0
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.01
V - Velocity (ft/sec) 3.02 3.02 3.02
Tc - Time of Conc. - Channel (min.)00 0
Time of Concentration (Ttotal)55 5
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr) 3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.56 0.67 0.93
Pipe Pipe Size
(in)
Flow Depth -
d (in)Slope (ft/ft) Manning's n
Provided
Capacity (cfs)
Required
Capacity (cfs)
PIPE E 8 6.00 0.005 0.012 0.84 0.67
Rainfall Frequency (yr)
Pipe Capacity
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Stormtech
C = Runoff Coefficient Facility Make/Model: SC 310
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 9 0 0.00 0.95 0.000
DB - Roof 9 8,000 0.18 0.95 0.174
DB - Pervious 9 0 0.00 0.20 0.000
Totals 8,000 0.18 0.1745
Weighted C:0.95
Total Area (Acres) = 0.18
Weighted C = 0.95
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.07
Req. Runoff Volume (ft3)=515
Total Ret Volume (ft3)540
Provided Retention (Stormte)
Storage Facility Calculations
STORMTECH SYSTEM E
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 10
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 10 0 0.00 0.95 0.0000
DB - Pervious 10 802 0.02 0.20 0.0037
DB - Roof 10 0 0.00 0.95 0.0000
Total 802 0.02 0.0037
Weighted C:0.20
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.95
C * Cf 0.95 1.05 1.19
D - Length of Basin (ft) 81
Sb - Slope of Basin (%)1.0000
To - Time of Conc. - Overland (min.)2.52 0.93 -1.47
L - Length of Channel (ft) 0
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.0062
V - Velocity (ft/sec) 2.38 2.38 2.38
Tc - Time of Conc. - Channel (min.)000
Time of Concentration (Ttotal)555
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr) 3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.01 0.01 0.02
Rainfall Frequency (yr)
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: Swale
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 10 0 0.00 0.95 0.000
DB - Roof 10 0 0.00 0.95 0.000
DB - Pervious 10 802 0.02 0.20 0.004
DB - Gravel 10 1,947 0.04 0.85 0.038
Totals 2,749 0.06 0.0417
Weighted C:0.66
Total Area (Acres) = 0.06
Weighted C = 0.66
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.02
Req. Runoff Volume (ft3)=123
Total Ret Volume (ft3)415
Provided Retention (Swale)
Storage Facility Calculations
Swale A
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Design Rainfall Frequency (year): 10 Storage Method: Retention
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: Infiltration
Q = Peak Runoff Rate (cfs)Facility Type: Dry Well
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 11 1,711 0.04 0.95 0.037
DB - Roof 11 0 0.00 0.95 0.000
DB - Pervious 11 0 0.00 0.20 0.000
Totals 1,711 0.04 0.0373
Weighted C:0.95
Total Area (Acres) = 0.04
Weighted C = 0.95
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.02
Req. Runoff Volume (ft3)=110
Total Ret Volume (ft3)Unknown
Provided Retention (Existing Drywell)
Storage Facility Calculations
Existing Loading Dock Dry Well
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Drainage Basin 12
Land Use
Drainage
Basin
Number
Contributing
Area (sf)
Contributing
Area (Ac)
Runoff
Coefficient
(C)
A (Ac) x C
DB - Impervious 12 0 0.00 0.95 0.0000
DB - Pervious 12 875 0.02 0.20 0.0040
DB - Roof 12 0 0.00 0.95 0.0000
Total 875 0.02 0.0040
Weighted C:0.20
10 25 100
Cf - Frequency Adjustment Factor 1 1.1 1.25
C - Runoff Coefficient (Overland Flow) 0.2
C * Cf 0.2 0.22 0.25
D - Length of Basin (ft) 5
Sb - Slope of Basin (%)25.0000
To - Time of Conc. - Overland (min.)1.29 1.26 1.22
L - Length of Channel (ft) 0
n - Manning's Coefficient 0.013
R - Hydraulic Radius(ft) 0.136
Sc - Slope of Channel (ft/ft) 0.0062
V - Velocity (ft/sec) 2.38 2.38 2.38
Tc - Time of Conc. - Channel (min.)000
Time of Concentration (Ttotal)555
X - Storm Duration (hr) 0.08 0.08 0.08
I - Intensity (in/hr) 3.22 3.83 5.34
Q - Peak Runoff (cfs) 0.01 0.02 0.02
Rainfall Frequency (yr)
Design Rainfall Frequency (year): 10 Storage Method: N/A
Rational Method Peak Runoff Equation: Q = CIA Discharge Method: N/A
Q = Peak Runoff Rate (cfs)Facility Type: N/A
C = Runoff Coefficient Facility Make/Model: N/A
I = Rainfall Intensity (in/hr): 0.41
A = Drainage Basin (acres)
Land Use Drainage Basin
Number Contributing Area (sf) Contributing Area (Ac)
Runoff Coe.
(C)A (Ac) x C
DB - Impervious 12 0 0.00 0.95 0.000
DB - Roof 12 0 0.00 0.95 0.000
DB - Pervious 12 875 0.02 0.20 0.004
DB - Gravel 12 0 0.00 0.85 0.000
Totals 875 0.02 0.0040
Weighted C:0.20
Total Area (Acres) = 0.02
Weighted C = 0.20
Duration (hrs) = 2.00
Intensity (in/hr) = 0.41
Q (cfs) = 0.00
Req. Runoff Volume (ft3)=12
Total Ret Volume (ft3)N/A
Provided Retention
Storage Facility Calculations
Drainage Basin 12 - Off Site
Basis For Calculations Storage Facility Information
Contributing Area & Runoff Coefficient Tabulation
Generated Runoff Volume - 10 year, 2 hour Storm
Appendix C
Groundwater Monitoring