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HomeMy WebLinkAbout005 NWX Chipotle Building - Storm Report STORM WATER DESIGN REPORT FOR CHIPOTLE BOZEMAN, MONTANA Prepared By: Morrison-Maierle, Inc. 2880 Technology Blvd. West P.O. Box 1113 Bozeman, Montana 59771-1113 Engineer: Celine M. Saucier, P.E. Date: April 17, 2024 File: 5659.022 __________________________________________________________________________________ CHIPOTLE STORM WATER DESIGN REPORT 2 CHIPOTLE STORM WATER DESIGN REPORT TABLE OF CONTENTS 1.0 Introduction ..................................................................................................... Page 3 2.0 Site Description ............................................................................................... Page 3 3.0 Underground Retention System Calculations ................................................. Page 3 4.0 Storm Drain Pipe Calculations........................................................................ Page 4 5.0 Groundwater…………………………………………………………………Page 4 6.0 Storm Water Maintenance Plan ...................................................................... Page 5 7.0 Summary ......................................................................................................... Page 5 LIST OF APPENDICES Appendix A. Post-development Runoff Calculations B. StormTech Sizing Calculations C. Conveyance Calculations __________________________________________________________________________________ CHIPOTLE STORM WATER DESIGN REPORT 3 CHIPOTLE STORM WATER DESIGN REPORT 1.0 Introduction This summary report provides hydrologic and hydraulic calculations for sizing of retention storage facilities and other storm drainage structures for development of the Northwest Crossing Building J commercial site, in accordance with the City of Bozeman Design Standards. The purpose of the report and calculations is to demonstrate the following: - Post- development peak runoff does not exceed pre-construction (historic) conditions for the 10-year storm event - The 25-year peak runoff is conveyed by underground storm drain facility with no surface overflow - Storm water treatment is provided to intercept and contain sediment and floating debris on site, for eventual removal and disposal. Improvements associated with the restaurant are utility services, including water, sanitary sewer and storm drainage as they do not currently exist on the site, as well as curb and gutter, asphalt other miscellaneous items and appurtenances. All storm drain runoff will be retained on-site. 2.0 Site Description Building J is a 33,972 square foot (0.78 acre) commercial site located in the Northwest Crossing development. The proposed site consists of a commercial building bordered on the South by West Oak Street, to the North by Dayspring Avenue, to the East by Lot 10 and to the West by Lot 12. The eastern property line is being extended to the east approximately 11 feet increasing the area of Lot 11 to 36,897 square feet (0.847 acres). This was considered for the calculations of the post development runoff values. The Northwest Crossing development is legally described as: Tract 5 of Certificate of Survey No. 2552, located in the NE1/4 of Section 4, Township 2 South, Range 5 East, Principal Meridian, Gallatin County, Montana. Storm water runoff from Lot 11 will be conveyed to one underground retention system. See Appendix A for the post development exhibit outlining proposed basins areas and drainage systems. This project is analyzed as a closed basin, with all storm water runoff handled onsite. The proposed parking lot will use a combination of storm collection. The use of manholes having grated inlet covers, will service most of the storm water collected. In addition, curb and gutter will line both sides of the drive aisles with strategically placed __________________________________________________________________________________ CHIPOTLE STORM WATER DESIGN REPORT 4 inlets to capture the remaining storm water. The 10-year, 2-hour storm was used to evaluate each retention system size. 3.0 Underground Retention System Calculations Storm drainage analysis and design is per the City of Bozeman Design Standards. The rational method is utilized for peak flow calculations for sizing the underground retention systems based on the 10-year, 2-hour storm intensity. All calculations are based on post- development values and are included in Appendix A. The site has been designed one underground retention system which will utilize ADS StormTech model SC-310. The installation of these units will include a stone foundation below and above the chambers a minimum of 6 inches, with the average cover above the chamber to be 18 inches. The stone to be used for the stormtech installation will have a porosity of 40%. See Appendix B for ADS SC-740 calculations and layout. Below is a table that summarizes the storage for each on-site drainage basin. Basin Intensity, i (in/hr) Total Area (acres) Post-development Peak Runoff (cfs) Required Storage (CF) Proposed Storage (CF) 1 .41 0.85 0.74 1,845 1,933 4.0 Storm Drain Pipe Calculations The storm drain piping system for the proposed development is designed to convey flows from a 25-year storm. Provisions for overland flow of larger, less frequent storms up to the 100-year storm will be incorporated into the site grading. The 25-year storm over the entire site at a time of concentration of 5 min has a runoff rate of 2.41 cfs. This flow rate was used to size the storm drain pipes through the site. The conveyance calculations for these pipes in Appendix C show that a 12” pipe at 0.5% slope will flow at 69% full and are adequate to convey the 25-year storm through the site. Additional design details are provided on the construction drawings. 5.0 Groundwater As a part of the Northwest Crossing subdivision a groundwater model was made in Autocad to predict the high groundwater throughout the site. The bottom of the chambers is designed to be as high as possible with elevation 36.35. In the high groundwater model, the highest groundwater was encountered at the furthest south chamber at an elevation of 36.00’. We understand that the city recommends a three-foot separation between high groundwater and the chamber bottom however the systems were designed to be placed as high as possible for this area given the elevation heigh was limited by the existing surrounding grades of Dayspring Avenue and the limitations of where we could place the system to avoid existing easements. __________________________________________________________________________________ CHIPOTLE STORM WATER DESIGN REPORT 5 6.0 Storm Water Maintenance Plan The maintenance of on-site storm water retention will be integrated as part of the maintenance of the restaurant. Duties shall include routine inspection to ensure that sediment, debris, yard waste, and seasonal ice does not impede operation of the storm drain facilities. It is recommended that these inspections occur after major runoff events and on a monthly basis throughout the year. 7.0 Summary The storm water analysis for the proposed Chipotle was completed using applicable state and local regulations/standards as well as sound engineering practices. The result is a storm water plan that provides for the conveyance and storage of storm water runoff while protecting private property and promoting public safety. APPENDIX A SDSDSD SD SD SD SD SDSDSDSD N89°30'03"E 145.78' S67°0 7' 2 5 " W 1 7 4 . 7 1' 158.51'N0°59'41"E 263.72'N89°57'07"W 149.49'S0°00'00"W 228.59'S89°57'07"E 12.00'S0°00'00"E 174.80'16.20'S0°59'08"W 45.90'1.89' 20.00' 21.00' C A B D FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE,2024 Plotted by celine saucier on Jun/5/2024 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net N:\5659\022 - NWX Lot 11 Site Plan\04 Design\Reports\Storm\Lot 11 Chipotle Storm areas.dwg5659.022  EX. 1 TJW CMS MONTANA STORM BASIN EXHIBIT NWX CHIPOTLE BUILDING CMS 11/2021 15 300 SCALE IN FEET SUB-BASIN TOTAL (SF)LANDSCAPE (SF)IMPERVIOUS (SF) A 2328.98 0 2328.98 B 21307.64 4931.82 16375.82 C 12147.68 3560.73 8586.95 D 1112.70 556.35 556.35 TOTAL 36,897 9048.90 27848.10 STORMTECH CHAMBERS RATIONAL METHOD FOR ANALYSIS OF STORM WATER RETENTION NWX CHIPOTLE Lot 11 | Pre-Development - 10 Year Design Storm Frequency Design Storm Frequency = Year Input values for runoff coefficients from appropriate tables. 1Weighted runoff coefficient, Cwd = SCjAj / Saj where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Calculation of Storm Water Runoff Flow Rate: Q = Storm Water Runoff Flow Rate (cfs) i = Rainfall Intensity (in/hr) Cwd = Weighted Runoff Coefficient A = Storm Drainage Basin Area (acres) Storm Drainage Basin Weighted Runoff Coefficient, Cwd = Rainfall Intensity, i =in/hr (10-year, 2-hour Design Storm) Storm Drainage Basin Area, A =acres Basin Design Peak Flow, Qp =cfs Calculation of Required Retention Volume: Q = Storm Water Runoff Flow Rate (cfs) V = Required Retention Volume (cf) Storm Drainage Basin Runoff Flow Rate, Q =cfs Basin Required Retention Volume, V = cf 10 (Enter WQual, 2, 5, 10, 25, 50, or 100) DRAINAGE BASIN CHARACTERISTICS Weighted Adjusted Runoff Runoff Runoff Frequency Coefficient Surface Area, A Area, A Coefficient Coefficient1 Factor C' = Cwd x Cf Description (ft2)(acres) C C x A Cwd Cf Cwd x Cf → Cwd x Cf ≤ 1.00 C' x A Hard Surface (back, sides parking) 27,848 0.639 0.95 0.607 0.74 1.000.20 0.74 Landscaping 9,049 0.208 0.10 0.021 Undeveloped 0.628 BASIN RETENTION VOLUME ANALYSIS 0.74 0.41 0.847 0.26 Totals 36,897 0.847 0.628 0.74 0.628 0.26 1,844.51 = = 7200 1 APPENDIX B User Inputs Chamber Model: SC-310 Outlet Control Structure: No Project Name: 5659.022 Chipotle Building Engineer: Trace Walker Project Location: Montana Measurement Type: Imperial Required Storage Volume: 1844 cubic ft. Stone Porosity: 40% Stone Foundation Depth: 6 in. Stone Above Chambers: 6 in. Design Constraint Dimensions:(60 ft. x 80 ft.) Results System Volume and Bed Size Installed Storage Volume: 1933.22 cubic ft. Storage Volume Per Chamber: 14.70 cubic ft. Number Of Chambers Required: 55 Number Of End Caps Required: 12 Chamber Rows: 6 Maximum Length:77.68 ft. Maximum Width: 21.50 ft. Approx. Bed Size Required: 1551.55 square ft. Average Cover Over Chambers: N/A . System Components Amount Of Stone Required: 105 cubic yards Volume Of Excavation (Not Including Fill): 135 cubic yards Total Non-woven Geotextile Required:476 square yards Woven Geotextile Required (excluding Isolator Row): 23 square yards Woven Geotextile Required (Isolator Row): 39 square yards Total Woven Geotextile Required:61 square yards Impervious Liner Required:0 square yards APPENDIX C RATIONAL METHOD FOR ANALYSIS OF STORM WATER RETENTION NWX CHIPOTLE Lot 11 - 25 Year Design Storm Frequency Design Storm Frequency = Year Input values for runoff coefficients from appropriate tables. 1Weighted runoff coefficient, Cwd = SCjAj / Saj where Cj is the adjusted runoff coefficient for surface type j and Aj is the area of surface type j Calculation of Storm Water Runoff Flow Rate: Q = Storm Water Runoff Flow Rate (cfs) i = Rainfall Intensity (in/hr) Cwd = Weighted Runoff Coefficient A = Storm Drainage Basin Area (acres) Storm Drainage Basin Weighted Runoff Coefficient, Cwd = Rainfall Intensity, i =in/hr (25-year, 2-hour Design Storm) Storm Drainage Basin Area, A =acres Basin Design Peak Flow, Qp =cfs 0.691 BASIN RETENTION VOLUME ANALYSIS 0.74 3.83 0.847 2.41 Totals 36,897 0.847 0.628 0.20 0.82 0.82 0.691 Landscaping 9,049 0.208 0.10 0.021 Undeveloped Cwd x Cf → Cwd x Cf ≤ 1.00 C' x A Hard Surface (back, sides parking) 27,848 0.639 0.95 0.607 0.74 1.10 C' = Cwd x Cf Description (ft2)(acres) C C x A Cwd Cf Coefficient Surface Area, A Area, A Coefficient Coefficient1 Factor Adjusted Runoff Runoff Runoff Frequency 25 (Enter WQual, 2, 5, 10, 25, 50, or 100) DRAINAGE BASIN CHARACTERISTICS Weighted = 1 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Apr 17 2024 12in Storm Pipe @ 0.5% Slope Circular Diameter (ft) = 1.00 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.011 Calculations Compute by: Known Q Known Q (cfs) = 2.41 Highlighted Depth (ft) = 0.69 Q (cfs) = 2.410 Area (sqft) = 0.58 Velocity (ft/s) = 4.16 Wetted Perim (ft) = 1.96 Crit Depth, Yc (ft) = 0.67 Top Width (ft) = 0.92 EGL (ft) = 0.96 0 1 2 3 Elev (ft)Depth (ft)Section 99.50 -0.50 100.00 0.00 100.50 0.50 101.00 1.00 101.50 1.50 102.00 2.00 Reach (ft) APPENDIX D