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DESIGN
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Storm Water Management Design Report
Current Landing, LLC Offices
Corner of Fallon and Laramie St.
Lot 2, Block 1 of
Parkway Plaza Subdivision
Bozeman, Montana
December 2023
Prepared By:
Genesis Engineering, Inc.
GEI Project #: 1154.004.040
Prepared For:
Current Landing, LLC
Bozeman, Montana
204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 2 of 7
Storm Water Management Design Report
Table of Contents
I. Project Background……………………………………………………………………………………………….. 4
1. Introduction………………………………………………………………………………………………………………. 4
2. Soil and Groundwater……………………………………………………………………………………………….. 4
3. Land Use……………………………………………………………………………………………………………………. 4
II. Existing Conditions…………………………………………………..………………………………………………. 4
1. Drainage Basins and Pre‐Development Peak Flows…………………………………………………… 4
III. Proposed Drainage Plan and Post‐Development Peak Flows…………………………………. 5
1. Major Drainage System…………………………………………………………………………………………….. 6
2. Minor Drainage System…………………………………………………………………………………………….. 6
3. Maintenance…………………………………………………………………………………………………………….. 7
IV. Conclusion………………………………………………………………………………………….……………………. 7
List of Tables
Table 1. Estimated Pre‐Development Peak Flows……………………………………………………………………….. 5
Table 2. Estimated Capacity of Existing Drainage Facilities…………………………………………………………. 5
Table 3. Estimated Post‐Development Peak Flows……………………………………………………………………… 5
Table 4. Required Pond Volumes ……………………………………..………………………………………………………… 6
Appendix A—Calculations
Grading and Drainage Exhibits
Pre/Post Development Runoff Computations
Storm Pond Computations
Gutter and Sidewalk Chase Flow Modeling
List of References
City of Bozeman Design Standards and Specifications Policy and all addenda.
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I. Project Background
Introduction
The Current Landing Project consists of 3 proposed office/storage buildings on an existing lot (2) within the existing
Parkway Plaza Subdivision and PUD. This existing lot is shaded in green in Figure 1 below and consists of approximately
1.37 acres, more specifically located at the corner of Fallon Street and Laramie Street in Bozeman, Gallatin County,
Montana.
Figure 1 – Lot 2 in Parkway Plaza Subdivision
This report outlines the storm water analysis conducted for the site and describes the storm water drainage and
management facilities necessary for the proposed project by state and local regulations. We also explore the capacity
of the existing stormwater facilities already provided for and how runoff from the proposed project fits into this existing
infrastructure. The proposed storm water plan follows the design standards set forth by the City of Bozeman in Design
Standards and Specifications Policy with subsequent addenda.
Soil and Groundwater
The NRCS Soil Survey identifies the major soil types on the site as Turner loam (457A). This soil belongs to hydrologic
soil group B as they are comprised primarily of loams and silt loams with moderately high saturated hydraulic
conductivity. Groundwater is depths range from 8’ to 12’ depending on the time of the year.
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Land Use
The existing land use is for business park offices as is currently proposed. The proposed storm water structures and
building elevations will conform to City land use requirements and zoning as it proceeds through the COB site plan
review process.
II. Existing Conditions
The site consists of an existing undeveloped subdivision lot. The ground cover is grass and the land slopes generally to
the north west at a grade of approximately 1.5% with the high point of the property located on the southeastern corner
of the existing subdivision lot. The natural grading conveys runoff in an overland fashion, to the south side of Fallon
Street. This can be seen on the attached exhibit showing the existing and proposed drainage basins. The proposed 3
commercial buildings are located as shown. The purpose of this design report is to size and design conveyance
structures and the attenuation storm pond for the area that is to be developed.
Drainage Basins and Pre‐development Peak Flows
Drainage basins were identified for the site. The offsite basins south and upstream of this subdivision lot will utilize the
existing street conveyance to the west and the irrigation ditch to the east convey runoff to the north. As for onsite
basins, basin A is comprised of the existing lot and the proposed development – office buildings and parking areas.
Estimates of runoff and their respective calculations for the basin subarea was completed using the Modified Rational
Method. The 10‐year, 25‐year, and 100‐year storm events were used in the analysis of the storm water conveyance
structures within the site. A summary of estimated pre‐development peak runoff rates can be found in Table 1.
Table 1. Estimated Pre‐Development Peak Flows (see basin map)
Sub Area Description Area C Tc Q10 Q25 Q100
(acres) (min) (cfs) (cfs) (cfs)
A Entire Site Plan 1.26 0.20 30 0.25 0.31 0.40
A‐1 See basin exhibit 0.22 0.20 7.7 0.11 0.13 0.18
A‐2 See basin exhibit 0.25 0.20 8.1 0.12 0.14 0.19
A‐3 See basin exhibit 0.12 0.20 8.2 0.10 0.11 0.15
III. Proposed Drainage Plan and Estimated Post‐Development Peak Flows
The proposed drainage plan shall utilize the existing drainage systems that are currently in place. Genesis’ drainage
plan consists of two drainage systems. First, we look at the major drainage system or backbone that consists of natural
streams, site grading, and street conveyance. These facilities are designed to have a much higher conveyance capacity
and shall convey the excess runoff from the 100‐year storm or greater without inundating any building structures.
Secondly, we look at the minor drainage system(s) that fit within the major drainage system and are designed to
accommodate moderate and relatively frequent or nuisance storm events without inconveniencing the public. The
minor drainage system(s) are comprised of the curb and gutters, inlets, piping, and shallow swales designed to convey
runoff from the 25‐year event, and also attenuation ponds designed for the 10‐year, 2 hour storm event.
In this particular project, the proposed drainage plan consists of four retention structures and a network of sidewalk
chases, and swales that are connected and within the proposed site plan. Please see the drainage basin exhibit in the
appendix for basin locations. Basin A will drain into the four stormwater storage structures that will provide retainage
of surface runoff from the proposed site. All storm chases are designed using a 25‐yr design storm event while the
retention structures are designed using the 10‐year, 2‐hour storm event. A summary of estimated post‐development
peak runoff rates can be found in Table 2. Proposed structure capacities can be found in Table 3 below.
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Table 2. Estimated Post‐Development Peak Flows (see basin map)
Basin Description Area C Tc Q10 Q25 Q100
(acres) (min) (cfs) (cfs) (cfs)
A Onsite 1.26 0.76 11.1 1.87 2.20 3.00
A1 Onsite 0.22 0.73 5 min 0.31 0.37 0.50
A2 Onsite 0.25 0.87 5 min 0.72 0.83 1.16
A3 Onsite 0.12 0.73 5 min 0.48 0.56 0.78
Table 3. Proposed Structure Capacities
Structure Slope Location Contributing QCap Q25post Passes Design
(%) Basins (cfs) (cfs) Storm
W. Side Walk Chase 1.0 SW Lot A1 2.3 0.37 Yes
E. Side Walk Chase 1.0 Mid Lot A2 2.3 0.83 Yes
N. Side Walk Chase 1.0 NE Lot A3 2.3 0.56 Yes
Pond 4 ‐ 12” Culvert 0.25 W BLD #3 A1 2.61 0.37 Yes
Pond 3 – 12” Culvert 0.25 W BLD #3 A1 2.61 0.37 Yes
Table 4. Estimated Retention Structure Volumes
Required Actual
Pond Type Contributing Q10Pre Q25post Qrelease Vol. Vol.
Subareas (cfs) (cfs) (cfs) (cft) (cft)
Pond 1 ‐ Retention Inf. Basin A 6.1 9.2 0 ‐ 2,000
Pond 2 ‐ Retention Basin A 6.1 9.2 0 ‐ 391
Pond 3 ‐ Retention Basin A 6.1 9.2 0 ‐ 212
Pond 4 ‐ Retention Basin A 6.1 9.2 0 ‐ 255
Total 1‐4 Retention ponds Basin A 6.1 9.2 0 2,793 2,858
Initial Storm Water Facilities Basin A NA NA NA 1,843 2,858
Temporary Phase 1 Pond Basin A 6.1 9.2 0 2,793 3,000
Maintenance
Regular maintenance of storm water facilities is necessary for proper functioning of the drainage system. In general,
regular mowing of any grass swales and storage ponds and unclogging of inlets and outlet works will be required to
prevent standing water, clogging, and the growth of weeds and wetland plants. More substantial maintenance, such as
sediment removal with heavy equipment, may be required in coming decades to restore detention pond volume.
All maintenance and repair should be prioritized and scheduled in advance. Inlets & pipes should be visually inspected
yearly. Typical maintenance items include removing obstructions, cleaning and flushing pipes, mowing grass and
weeds, tree maintenance to prevent limbs from falling and blocking swales, and establishing groundcover on bare
ground.
INFILTRATOR ‐ CMP RETENTION SYSTEM INSPECTION AND MAINTENANCE
UNDERGROUND STORMWATER RETENTION AND INFILTRATION SYSTEMS MUST BE INSPECTED AND MAINTAINED AT
REGULAR INTERVALS FOR PURPOSES OF PERFORMANCE AND LONGEVITY.
INSPECTION
INSPECTION IS THE KEY TO EFFECTIVE MAINTENANCE OF CMP DETENTION SYSTEMS AND IS EASILY PERFORMED.
CONTECH RECOMMENDS ONGOING, ANNUAL INSPECTIONS. SITES WITH HIGH TRASH LOAD OR SMALL OUTLET
CONTROL ORIFICES MAY NEED MORE FREQUENT INSPECTIONS. THE RATE AT WHICH THE SYSTEM COLLECTS
POLLUTANTS WILL DEPEND MORE ON SITE SPECIFIC ACTIVITIES RATHER THAN THE SIZE OR CONFIGURATION OF THE
SYSTEM.
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INSPECTIONS SHOULD BE PERFORMED MORE OFTEN IN EQUIPMENT WASHDOWN AREAS, IN CLIMATES WHERE
SANDING AND/OR SALTING OPERATIONS TAKE PLACE, AND IN OTHER VARIOUS INSTANCES IN WHICH ONE WOULD
EXPECT HIGHER ACCUMULATIONS OF SEDIMENT OR ABRASIVE/ CORROSIVE CONDITIONS. A RECORD OF EACH
INSPECTION IS TO BE MAINTAINED FOR THE LIFE OF THE SYSTEM
MAINTENANCE
CMP DETENTION SYSTEMS SHOULD BE CLEANED WHEN AN INSPECTION REVEALS ACCUMULATED SEDIMENT OR TRASH
IS CLOGGING THE DISCHARGE ORIFICE. ACCUMULATED SEDIMENT AND TRASH CAN TYPICALLY BE EVACUATED
THROUGH THE MANHOLE OVER THE OUTLET ORIFICE. IF MAINTENANCE IS NOT PERFORMED AS RECOMMENDED,
SEDIMENT AND TRASH MAY ACCUMULATE IN FRONT OF THE OUTLET ORIFICE. MANHOLE COVERS SHOULD BE
SECURELY SEATED FOLLOWING CLEANING ACTIVITIES. CONTECH SUGGESTS THAT ALL SYSTEMS BE DESIGNED WITH AN
ACCESS/INSPECTION MANHOLE SITUATED AT OR NEAR THE INLET AND THE OUTLET ORIFICE. SHOULD IT BE NECESSARY
TO GET INSIDE THE SYSTEM TO PERFORM MAINTENANCE ACTIVITIES, ALL APPROPRIATE PRECAUTIONS REGARDING
CONFINED SPACE ENTRY AND OSHA REGULATIONS SHOULD BE FOLLOWED.
ANNUAL INSPECTIONS ARE BEST PRACTICE FOR ALL UNDERGROUND SYSTEMS. DURING THIS INSPECTION, IF EVIDENCE
OF SALTING/DE‐ICING AGENTS IS OBSERVED WITHIN THE SYSTEM, IT IS BEST PRACTICE FOR THE SYSTEM TO BE RINSED,
INCLUDING ABOVE THE SPRING LINE SOON AFTER THE SPRING THAW AS PART OF THE MAINTENANCE PROGRAM FOR
THE SYSTEM. MAINTAINING AN UNDERGROUND DETENTION OR INFILTRATION SYSTEM IS EASIEST WHEN THERE IS NO
FLOW ENTERING THE SYSTEM. FOR THIS REASON, IT IS A GOOD IDEA TO SCHEDULE THE CLEANOUT DURING DRY
WEATHER. THE FOREGOING INSPECTION AND MAINTENANCE EFFORTS HELP ENSURE UNDERGROUND PIPE SYSTEMS
USED FOR STORMWATER STORAGE CONTINUE TO FUNCTION AS INTENDED BY IDENTIFYING RECOMMENDED REGULAR
INSPECTION AND MAINTENANCE PRACTICES. INSPECTION AND MAINTENANCE RELATED TO THE STRUCTURAL
INTEGRITY OF THE PIPE OR THE SOUNDNESS OF PIPE JOINT CONNECTIONS IS BEYOND THE SCOPE OF THIS GUIDE.
IV. Conclusion
Our Storm water analysis and calculations indicate that the proposed storm water facilities and management plan for
the site plan is adequate to safely convey the 10‐year, 25‐year, and 100‐year storm events and to satisfy state and local
regulations for 10‐year peak attenuation utilizing the proposed retention ponds onsite.
H:\1154\004\DOCS\DESIGN\STORM\WP\StormwaterDR.doc
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Appendix A
Calculations
Current Landing, LLC
Condominium Owners’ Association
Appendix A
Storm Water Facilities Operation & Maintenance Manual
Overview
The COA is responsible for maintaining all Storm Water Facilities, including storm inlets, sidewalk
chases, curb cuts, outlet structures, storm pipe and the storm water detention pond located within
the open space area of the Current Landing Site Plan.
Maintenance
The storm inlets and pond outlet structures shall have the sediment removed from the sediment
traps on a yearly basis or an updated maintenance schedule as determined by monitoring the
sediment build‐up of the inlets quarterly.
The storm pipe between the storm ponds and inlets is to be monitored yearly for build‐up of
sediment or trash. If the storm system is operating correctly, the build‐up should be minimal and
therefore the maintenance schedule will be directly correlated to the yearly inspection findings.
The storm water attenuation pond(s) shall be monitored every five years for sediment build‐up.
When the sediment build‐up starts to decrease the capacity of the attenuation pond, the sediment
shall be removed mechanically and hauled from the site. It the extraction of the sediment removes
the vegetation from the bottom of the pond, it should be reseeded or re‐sodded and appropriate
storm water BMPs are to be installed until the vegetation is stabilized.
Curb cuts and sidewalk chases should be monitored every 6 months for sediment build‐up or
blockage. A common issue with these storm facilities is the build‐up of grass at the daylight that
impedes flow and collects sediment. These facilities should be cleaned yearly or more frequently if
deemed necessary during the inspections. The sediment, trash and vegetation should be hauled
offsite.
Contact Information and signatures
Property Manager:_____________________________ Date: __________
Association President:__________________________ Date:__________
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Appendix A
Calculations
CURRENT LANDING 12/5/2022
BASIN A - PRE DEV BASIN A - POST DEV
Weighted C Weighted C
Area (sf) 54,933.00 Area (sf) 54,933.00
Area (Acres) 1.26 Area (Acres) 1.26
Area Impervious (0.9) - Area Impervious (0.9) 44,222.00
Area Native Grass (0.2) 54,933.00 Area Native Grass (0.2) 10,711.00
Weighted C= 0.20 Weighted C= 0.76
BASIN A1 - PRE DEV BASIN A1 - POST DEV
Weighted C Weighted C
Area (sf) 9,572.00 Area (sf) 9,572.00
Area (Acres) 0.22 Area (Acres) 0.22
Area Impervious (0.9) - Area Impervious (0.9) 7,186.00
Area Native Grass (0.2) 9,572.00 Area Native Grass (0.2) 2,386.00
Weighted C= 0.20 Weighted C= 0.73
BASIN A2 - PRE DEV BASIN A2 - POST DEV
Weighted C Weighted C
Area (sf) 11,070.00 Area (sf) 11,070.00
Area (Acres) 0.25 Area (Acres) 0.25
Area Impervious (0.9) - Area Impervious (0.9) 10,650.00
Area Native Grass (0.2) 11,070.00 Area Native Grass (0.2) 420.00
Weighted C= 0.20 Weighted C= 0.87
BASIN A3 - PRE DEV BASIN A3 - POST DEV
Weighted C Weighted C
Area (sf) 5,403.00 Area (sf) 5,403.00
Area (Acres) 0.12 Area (Acres) 0.12
Area Impervious (0.9) - Area Impervious (0.9) 4,069.00
Area Native Grass (0.2) 5,403.00 Area Native Grass (0.2) 1,334.00
Weighted C= 0.20 Weighted C= 0.73
Time of Concentration Calcs2 year 24 hr P = 1.272 (in)CURRENT LANDINGPre Delt H Length Slope n L sheet TC sheet L Shallow Velocity Fig 9TC Shallow Tc TotalBasin(ft) (ft) (ft/ft) (ft) (min) (ft) (ft/sec) (min) (min)A 3 350 0.009 0.1 200 27.5 150 1.0 2.5 30.0A1 2 120 0.017 0.1 50 6.9 70 1.5 0.8 7.7A2 3 170 0.018 0.1 50 6.8 120 1.5 1.3 8.1A3 0.5 112 0.004 0.1 25 6.8 87 1.0 1.5 8.2Post Delt H Length Slope n L sheet TC sheet L Shallow Velocity Fig 9TC Shallow Tc TotalBasin(ft) (ft) (ft/ft) (ft) (min) (ft) (ft/sec) (min) (min)A 3 350 0.009 0.05 100 9.1 250 2.0 2.1 11.1A1 2 120 0.017 0.05 50 4.0 70 2.5 0.5 4.5A2 3 170 0.018 0.05 50 3.9 120 2.5 0.8 4.7A3 0.5 112 0.004 0.05 25 3.9 87 2.0 0.7 4.6Figure 9 ‐ DEQ 8
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =10YR (DURATION = 1)
BASIN AREA PRE =1.26AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc = 30.0 MIN 0.50 2 0.36 0.6 0.55
5 0.52 0.64 0.81
PRE‐DEV C = 0.20 10 0.64 0.66 1.01
25 0.78 0.64 1.22
STORM A = 0.64 50 0.92 0.66 1.45
B = 0.66 100 1.01 0.67 1.61
STORM INTENSITY =1.01IN/HR
PRE‐DEV Qp =0.25CFS
BASIN AREA PRE =1.26AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.76
STORM INTENSITY =1.95IN/HR
POST‐DEV Qp =1.87CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A ‐ 10yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A-10yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =25YR (DURATION = 1)
BASIN AREA PRE =1.26AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc = 30.0 MIN 0.50 2 0.36 0.6 0.55
5 0.52 0.64 0.81
PRE‐DEV C = 0.20 10 0.64 0.66 1.01
25 0.78 0.64 1.22
STORM A = 0.78 50 0.92 0.66 1.45
B = 0.64 100 1.01 0.67 1.61
STORM INTENSITY =1.22IN/HR
PRE‐DEV Qp =0.31CFS
BASIN AREA PRE =1.26AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.76
STORM INTENSITY =2.30IN/HR
POST‐DEV Qp =2.20CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A ‐ 25yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A-25yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ = 100 YR (DURATION = 1)
BASIN AREA PRE =1.26AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc = 30.0 MIN 0.50 2 0.36 0.6 0.55
5 0.52 0.64 0.81
PRE‐DEV C = 0.20 10 0.64 0.66 1.01
25 0.78 0.64 1.22
STORM A = 1.01 50 0.92 0.66 1.45
B = 0.67 100 1.01 0.67 1.61
STORM INTENSITY =1.61IN/HR
PRE‐DEV Qp =0.40CFS
BASIN AREA PRE =1.26AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.76
STORM INTENSITY =3.13IN/HR
POST‐DEV Qp =3.00CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A ‐ 100yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A-100yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =10YR (DURATION = 1)
BASIN AREA PRE =0.22AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =7.7MIN 0.13 2 0.36 0.6 1.23
5 0.52 0.64 1.93
PRE‐DEV C = 0.20 10 0.64 0.66 2.48
25 0.78 0.64 2.90
STORM A = 0.64 50 0.92 0.66 3.57
B = 0.66 100 1.01 0.67 4.00
STORM INTENSITY =2.48IN/HR
PRE‐DEV Qp =0.11CFS
BASIN AREA PRE =0.22AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.73
STORM INTENSITY =1.95IN/HR
POST‐DEV Qp =0.31CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A1 ‐ 10yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A1-10yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =25YR (DURATION = 1)
BASIN AREA PRE =0.22AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =7.7MIN 0.13 2 0.36 0.6 1.23
5 0.52 0.64 1.93
PRE‐DEV C = 0.20 10 0.64 0.66 2.48
25 0.78 0.64 2.90
STORM A = 0.78 50 0.92 0.66 3.57
B = 0.64 100 1.01 0.67 4.00
STORM INTENSITY =2.90IN/HR
PRE‐DEV Qp =0.13CFS
BASIN AREA PRE =0.22AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.73
STORM INTENSITY =2.30IN/HR
POST‐DEV Qp =0.37CFS
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)i = A * (Tc/60) ‐B
STORM i COEFF
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A1 ‐ 25yr
H:\1154\004\DOCS\DESIGN\STORM\BASIN A1-25yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ = 100 YR (DURATION = 1)
BASIN AREA PRE =0.22AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =7.7MIN 0.13 2 0.36 0.6 1.23
5 0.52 0.64 1.93
PRE‐DEV C = 0.20 10 0.64 0.66 2.48
25 0.78 0.64 2.90
STORM A = 1.01 50 0.92 0.66 3.57
B = 0.67 100 1.01 0.67 4.00
STORM INTENSITY =4.00IN/HR
PRE‐DEV Qp =0.18CFS
BASIN AREA PRE =0.22AC
POST‐DEV Tc = 11.1 MIN
POST‐DEV C =0.73
STORM INTENSITY =3.13IN/HR
POST‐DEV Qp =0.50CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A1 ‐ 100yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A1-100yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =10YR (DURATION = 1)
BASIN AREA PRE =0.25AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.1MIN 0.14 2 0.36 0.6 1.20
5 0.52 0.64 1.87
PRE‐DEV C = 0.20 10 0.64 0.66 2.40
25 0.78 0.64 2.81
STORM A = 0.64 50 0.92 0.66 3.45
B = 0.66 100 1.01 0.67 3.86
STORM INTENSITY =2.40IN/HR
PRE‐DEV Qp =0.12CFS
BASIN AREA PRE =0.25AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.87
STORM INTENSITY =3.30IN/HR
POST‐DEV Qp =0.72CFS
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)i = A * (Tc/60) ‐B
STORM i COEFF
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A2 ‐ 10yr
H:\1154\004\DOCS\DESIGN\STORM\BASIN A2-10yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =25YR (DURATION = 1)
BASIN AREA PRE =0.25AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.1MIN 0.14 2 0.36 0.6 1.20
5 0.52 0.64 1.87
PRE‐DEV C = 0.20 10 0.64 0.66 2.40
25 0.78 0.64 2.81
STORM A = 0.78 50 0.92 0.66 3.45
B = 0.64 100 1.01 0.67 3.86
STORM INTENSITY =2.81IN/HR
PRE‐DEV Qp =0.14CFS
BASIN AREA PRE =0.25AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.87
STORM INTENSITY =3.83IN/HR
POST‐DEV Qp =0.83CFS
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)i = A * (Tc/60) ‐B
STORM i COEFF
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A2 ‐ 25yr
H:\1154\004\DOCS\DESIGN\STORM\BASIN A2-25yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ = 100 YR (DURATION = 1)
BASIN AREA PRE =0.25AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.1MIN 0.14 2 0.36 0.6 1.20
5 0.52 0.64 1.87
PRE‐DEV C = 0.20 10 0.64 0.66 2.40
25 0.78 0.64 2.81
STORM A = 1.01 50 0.92 0.66 3.45
B = 0.67 100 1.01 0.67 3.86
STORM INTENSITY =3.86IN/HR
PRE‐DEV Qp =0.19CFS
BASIN AREA PRE =0.25AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.87
STORM INTENSITY =5.34IN/HR
POST‐DEV Qp =1.16CFS
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)i = A * (Tc/60) ‐B
STORM i COEFF
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A2 ‐ 100yr
H:\1154\004\DOCS\DESIGN\STORM\BASIN A2-100yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =10YR (DURATION = 1)
BASIN AREA PRE =0.2AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.2MIN 0.14 2 0.36 0.6 1.19
5 0.52 0.64 1.86
PRE‐DEV C = 0.20 10 0.64 0.66 2.38
25 0.78 0.64 2.79
STORM A = 0.64 50 0.92 0.66 3.42
B = 0.66 100 1.01 0.67 3.83
STORM INTENSITY =2.38IN/HR
PRE‐DEV Qp =0.10CFS
BASIN AREA PRE =0.2AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.73
STORM INTENSITY =3.30IN/HR
POST‐DEV Qp =0.48CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A3 ‐ 10yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A3-10yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ =25YR (DURATION = 1)
BASIN AREA PRE =0.2AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.2MIN 0.14 2 0.36 0.6 1.19
5 0.52 0.64 1.86
PRE‐DEV C = 0.20 10 0.64 0.66 2.38
25 0.78 0.64 2.79
STORM A = 0.78 50 0.92 0.66 3.42
B = 0.64 100 1.01 0.67 3.83
STORM INTENSITY =2.79IN/HR
PRE‐DEV Qp =0.11CFS
BASIN AREA PRE =0.2AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.73
STORM INTENSITY =3.83IN/HR
POST‐DEV Qp =0.56CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A3 ‐ 25yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A3-25yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
RAINFALL FREQ = 100 YR (DURATION = 1)
BASIN AREA PRE =0.2AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE‐DEV Tc =8.2MIN 0.14 2 0.36 0.6 1.19
5 0.52 0.64 1.86
PRE‐DEV C = 0.20 10 0.64 0.66 2.38
25 0.78 0.64 2.79
STORM A = 1.01 50 0.92 0.66 3.42
B = 0.67 100 1.01 0.67 3.83
STORM INTENSITY =3.83IN/HR
PRE‐DEV Qp =0.15CFS
BASIN AREA PRE =0.2AC
POST‐DEV Tc =5.0MIN
POST‐DEV C =0.73
STORM INTENSITY =5.34IN/HR
POST‐DEV Qp =0.78CFS
1154.004
CHRIS WASIA
12/5/2022
POST‐DEVELOPMENT
Qp = C i A
BASIN A3 ‐ 100yr
i = A * (Tc/60) ‐B
STORM i COEFF
PRE‐DEVELOPMENT
MODIFIED RATIONAL METHOD
(CITY OF BOZEMAN)
H:\1154\004\DOCS\DESIGN\STORM\BASIN A3-100yr.xls 1 OF 1 PRINTED: 12/14/2022
GEI#:
DATE:
ENGINEER:
POND
RAINFALL FREQ = 10 YR (DURATION = 1)
BASIN AREA PRE = 1.26 AC STORM EVENT INTENSITY
(YR) A B (IN/HR)
PRE-DEV Tc = 30.0 MIN 0.50 2 0.36 0.60 0.55
5 0.52 0.64 0.81
PRE-DEV C = 0.20 10 0.64 0.66 1.01
25 0.78 0.64 1.22
STORM A = 0.64 50 0.92 0.66 1.45
B = 0.66 100 1.01 0.67 1.61
STORM INTENSITY = 1.01 IN/HR
PRE-DEV Qp = 0.25 CFS
POND VOLUME:
BASIN AREA PRE = 1.26 AC
POST-DEV Tc = 11.1 MIN 0.00
DETENTION
POST-DEV C = 0.76
INIT ST. FACILITY
STORM INTENSITY = 1.95 IN/HR (CF)
1,843
POST-DEV Qp = 1.87 CFS
DEQ RETENTION
(CF)
POND: POND A - 10YR 3,260
REQUIRED VOL =0.00 CF
DIAMETER = 12.00 IN
LENGTH OF PIPE = 20.00 FT QPRE = 0.25 CFS
HEAD WATER = 1.50 FT AREA = 0.11 SF
N = 0.012 ORIFICE = 4.59 IN
Ke = 0.50 ORIFICE FLOW = 0.68 CFS
SLOPE OF PIPE = 0.010 FT/FT
FLOW OUT = 3.70 CFS **NEED ORIFICE
AVE SURF AREA = 801.57 SF
POND A - 10YR
PRE-DEVELOPMENT
MODIFIED RATIONAL METHOD
(CF)
CONST.RELEASE
2,793
AVERAGE VOLUME
(CF)
(AVG. B/W CONST. & TRIANGLE RELEASE)
i = A * (Tc/60) -B
STORM i COEFF
(CF)
1,202
TRIANGLE RELEASE
1154.004
CHRIS WASIA
12/5/2022
1,497
1,791
COB RETENTIONOUTLET STRUCTURE DESIGN
POST-DEVELOPMENT
Qp = C i A
(CF)
H:\Engineering Resources\Storm\Rational Method\POND A-10yr.xls 1 OF 2 PRINTED: 12/14/2022
Qp = C i A
1.26 AC
11.1 MIN
0.76
1.949 IN/HR
1.87 CFS DURATION = 1
MAX VOLUME MAX VOLUME
AVERAGE
DETENTION VOL
(CFT) (CFT) (CFT)
1791.23 1202.36 1,496.79
10 Year 2hr 2 year 24hr
Triangle Release Constant Release COB DEQ 8
DURATION INTENSITY Qp POND VOLUME POND VOLUME RETENTION RETENTION
(MIN) (IN/HR) (CFS) (CF) (CF) (CF) (CF)
10.55 2.02 1.93 1056.13 913.05 2,793 3,260
11.55 1.90 1.82 1086.70 937.36
12.55 1.80 1.72 1115.14 959.50 0.64 = A = 0.36 2YR
13.55 1.71 1.64 1141.74 979.75 0.66 = B = 0.60 2YR
14.55 1.63 1.56 1166.70 998.34 120 = tc = 1440 min (24 hr duration given by DEQ 8)
15.55 1.56 1.49 1190.21 1015.45 0.405 = i = 0.053 in/hr
16.55 1.50 1.43 1212.43 1031.24 Qpost = 0.051 CFS
17.55 1.44 1.38 1233.48 1045.83 0.388 = Qpre = 0.013 CFS
18.55 1.39 1.33 1253.47 1059.34
19.55 1.34 1.28 1272.49 1071.87 DEQ 8
20.55 1.30 1.24 1290.62 1083.48 INTIAL STORMWATER FACILITY
21.55 1.26 1.20 1307.94 1094.27 (CF)
22.55 1.22 1.17 1324.51 1104.28 1,843
23.55 1.19 1.14 1340.38 1113.58
24.55 1.15 1.11 1355.60 1122.21 Aimp = 44,222.00 sqft
25.55 1.12 1.08 1370.21 1130.22
26.55 1.10 1.05 1384.25 1137.65
POND A - 10YR
POST-DEV Qp =
POND VOLUME CALCULATIONS:
MODIFIED RATIONAL METHOD
POST-DEVELOPMENT
BASIN AREA PRE =
POST-DEV Tc =
POST-DEV C =
STORM INTENSITY =
1 CURRENT LANDING
Pond Volume use
Basin A - Retention Pond
Layer Elevation Area Volume
(ft) (sqft) (cft)
14268
2 44 1901 1969
Total 1969 cft
2 CURRENT LANDING
Pond Volume use
Basin A - Retention Pond
Layer Elevation Area Volume
(ft) (sqft) (cft)
14317
2 45 572 589
Total 589 cft
3 CURRENT LANDING
Pond Volume use
Basin A - Retention Pond
Layer Elevation Area Volume
(ft) (sqft) (cft)
14423
2 45.7 290 266.05
Total 266.05 cft
4 CURRENT LANDING
Pond Volume use
Basin A - Retention Pond
Layer Elevation Area Volume
(ft) (sqft) (cft)
14411
2 46 291 302
Total 302 cft
Provided 3126 cft
Required 2793 cft
Delta 333 cft long