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Home My WebLink About23073 Stormwater Report ENGINEERING CONSULTING PLANNING DESIGN 204 N. 11th Ave.  BOZEMAN, MT 59715  406‐581‐3319  www.g‐e‐i.net 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 1 of 7 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. 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 3 of 7 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. 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 4 of 7 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. 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 5 of 7 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. 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 6 of 7 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 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 7 of 7 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:__________ 204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 6 of 6 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