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HomeMy WebLinkAboutKb StormWater Design Report STORM WATER DESIGN REPORT FOR HOME 2 HOTEL BOZEMAN, MONTANA Prepared By: Morrison-Maierle, Inc. 2880 Technology Blvd. West P.O. Box 1113 Bozeman, Montana 59771-1113 Engineer: Celine Saucier, P.E. Date: March 3, 2020 File: 2605.028 __________________________________________________________________________________ HOME 2 HOTEL – BOZEMAN STORM WATER DESIGN REPORT 2 HOME 2 HOTEL - BOZEMAN STORM WATER DESIGN REPORT TABLE OF CONTENTS 1.0 Introduction ..................................................................................................... Page 3 2.0 Existing Conditions ......................................................................................... Page 3 3.0 Saccoccia Minor Subdivision Design ............................................................. Page 3 4.0 Proposed Conditions ....................................................................................... Page 4 5.0 Conveyance ..................................................................................................... Page 5 6.0 Summary ......................................................................................................... Page 5 LIST OF APPENDICES Appendix A. Proposed Basins B. City of Bozeman Intensity-Duration-Frequency Curve (IDF) C. On-Site Basin Hydrology and Calculations D. Storm Drain Pipe Calculations __________________________________________________________________________________ HOME 2 HOTEL – BOZEMAN STORM WATER DESIGN REPORT 3 HOME 2 HOTEL - BOZEMAN STORM WATER DESIGN REPORT 1.0 Introduction This report provides the hydrologic and hydraulic calculations for development of a Home 2 Hotel on Baxter Lane. The site is located on Lot 2A in the 23-acre Saccoccia Subsequent Minor Subdivision (2006). Lot 2A is also in the 40-acre Planned Unit Development (PUD) for the Lowe’s Home Improvement Warehouse (2002). The PUD and subsequent minor subdivision include drainage calculations for a single, site wide detention pond that was constructed, as a part of the Lowe’s Home Improvement Warehouse project, to serve the entire PUD upon fully developed conditions. This report is an addendum to the previous Saccoccia Minor Subdivision Basis of Design Report, January 2007 to demonstrate consistency with the assumptions made in the previous report. The previous reports assumed storm runoff from Lot 2A would generally drain east to the detention pond, which would provide storm water treatment and detention to the 10-year pre-development peak runoff rate, as required by the City of Bozeman. 2.0 Existing Conditions The site is located south of Baxter Lane, between Simmental Way and Sacco Drive. Existing ground cover is undeveloped, agricultural fields. Pre-development topography is gradual, sloping at about one percent from south to north. Under existing conditions surface water falls on entirely undeveloped agricultural land and runs north collecting in natural closed depressions along the east and north edges of the site. These closed depressions, if filled with runoff, would overtop into Baxter Lane, or in an easterly direction to the existing detention pond. 3.0 Saccoccia Minor Subdivision Design Per the Saccoccia Minor Subdivision Basis of Design Report, the stormwater for all lots is directed to a regional detention pond located in the northeast corner of the subdivision. The pond was sized and constructed as part of the Lowe’s HIW PUD, accounting for all the land within the Saccoccia Minor Subdivision in the design of the detention pond associated with this PUD. The intent was for the individual lots to capture stormwater by grading to catch basins or sheet draining directly to swales that will be conveyed either though piping or open channels to the regional detention pond. The Saccoccia Minor Subdivision currently utilizes this detention pond to attenuate the increase from pre- development to post-development flows prior to discharging into the Walton’s Stream/Ditch. To simplify the phasing of the planned unit development, the entire detention pond was built during the first phase of construction. By building out the entire pond at one time, __________________________________________________________________________________ HOME 2 HOTEL – BOZEMAN STORM WATER DESIGN REPORT 4 disturbance of the detention area can be avoided during the final phasing of the development. The detention pond was sized according to the City of Bozeman Design Standards and Specifications Policy. The modified rational method was used to compare the predevelopment and post development runoff rates using the formula Q = CiA. The post development runoff rate for the subdivision was calculated using a conservative composite C of 0.76. The detention pond was sized by subtracting the total basin release volume from the allowable pre-development runoff at different storm durations. For the entire subdivision, the required storage volume was designed to be 44,860 cf (see the Saccoccia Minor Subdivision Basis of Design Report for calculations). 4.0 Proposed Conditions Under proposed (developed) conditions, site runoff on the north end of the site would drain into the existing swale to the north. The runoff from the site to the south will be collected in the parking lot and directed to a temporary pond which would then outlet to the east into the detention pond designed to detain the runoff for the PUD. The proposed site is divided into separate basins shown in Appendix A. Area: Calculated in AutoCAD (2.22 impervious, 1.35 pervious) C (Rational Method runoff coefficient): Runoff coefficients for the Home 2 development were calculated using 0.2 for pervious area (pre-development and developed landscape areas), 0.65 for gravel area, and 0.9 for impervious areas (pavement, concrete and rooftops). Pro-rating by area resulted in the coefficients used in the calculations and a composite coefficient of 0.64. Tc (time of concentration): Determined based on the time required for runoff to travel from the hydraulically most distant point to the outlet. The Tc of 6.2 min from the original drainage report was used as this number considers the most hydraulically distant point. Storm Intensity: Determines the 10-year storm intensity at the time of concentration Peak Runoff (Qp): Value calculated using the Ration Method formula (Q = C i A) and the intensity formulas in the City’s design standards (Rainfall Intensity – Duration Curve). The Peak Runoff for the 10-year design storm of the proposed development and is calculated to be 4.49cfs with a required detention storage of 2,099. In comparison, the peak runoff utilizing the conservative coefficient of 0.76 yields a peak runoff of 7.76cfs and a required detention storage of 2,792cuft. Therefore, the PUD’s detention pond calculations overestimated by a volume of 693 cuft. See Appendix C for 10-year design storm calculations. __________________________________________________________________________________ HOME 2 HOTEL – BOZEMAN STORM WATER DESIGN REPORT 5 5.0 Conveyance The storm drain pipe being proposed for the site will convey water to the detention pond to the east. Inlets throughout the site will collect the water. The piping, in accordance with City Standards shall be designed to accommodate the 25-year storm event. See Appendix C for 25-year design storm calculations. North Side Culverts The culverts to the north of the building will convey the 25-year flow for Basin 1. For Basin 1, a 25-year flow of 2.536cfs is used. 12” culverts will be installed at a minimum slope of 0.5% at each sidewalk crossing and will be approximately 66% full. South Side Collection Pipe The collection piping to the south of the building will be used to convey flows from future Basins 2 and southern Basins 3 and 4. For Basin 2, a conservative coefficient of 0.76 from the original PUD report was used. See the following table for a summary of the conveyance through the development. Coefficient (C) 25-year Storm Flow Rate (cfs) Pipe/Culvert Size Minimum Slope Maximum Flow (cfs) Percent Full Basin 1 0.56 2.54 12” RCP Culvert 0.5% 3.197 66% Basin 2 0.76 5.07 15” HP Piping 0.5% 5.797 78% Basin 2,3 0.76 6.31 18” HP Piping 0.5% 9.428 63% Basin 2,3,4 0.72 10.30 21” HP Piping 0.3% 11.02 83% All conveyance piping calculations are included in Appendix D. 6.0 Summary The storm water analysis for the proposed Home 2 Hotel 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, storage and treatment of storm water. Since the composite developed coefficient for the development was found to be 0.64, which is less than the 0.76 coefficient that was assumed in the PUD’s detention calculations, it can be assumed that there is adequate capacity in the existing pond for the runoff from the proposed development. APPENDIX A PROPOSED HOTEL103 UNITS103 PARKING STALLSHYDTVTDDPPLOWES SIGNN87°00'45"W 397.99'20.00'75.43'20.00'74.60' 30.00'86.72'117.02'60.00' 117.67'45.01' 45.01' S2°55'47"W 162.68'S85°50'42"E 398.05'OHPOHPOHPOHPOHPOHPOHPOHPOHPPTVLOT 2ACORRECT AMENDEDPLAT NO. 407CLOT 1ABTVGGWVDYH N87°02'06"W 796.17'S2°57'21"W 377.59'S85°50'42"E 398.33'S85°50'42"E 398.05'VERIFY SCALE!THESE PRINTS MAY BE REDUCED.LINE BELOW MEASURES ONE INCHON ORIGINAL DRAWING. MODIFY SCALE ACCORDINGLY!2020COPYRIGHT © MORRISON-MAIERLE, INC.,SHEET NUMBERPROJECT NUMBERDRAWING NUMBERDATEDESCRIPTIONNO.BYN:\2605\028 - HOME 2\ACAD\EXHIBITS\STORM DRAIN BASIN MAP.DWG PLOTTED BY:CELINE SAUCIER ON Mar/03/2020REVISIONSDRAWN BY:DSGN. BY:APPR. BY:DATE:Q.C. REVIEWDATE:BY:2880 Technology Boulevard WestBozeman, MT 59718406.587.0721www.m-m.netengineers surveyors planners sci entistsMorrisonMaierleHOME 2 - HOTEL 2605.028MONTANABASIN MAPFIG 1CMSCMS MEE2/21/2020TEE6/24/2019BOZEMANE. BAXTER LANEBASIN 1 - 1.33 ACRES@ C = 0.56BASIN 4 - 1.76 ACRES@ C = 0.65BASIN 2 - 1.96 ACRES@ C = 0.76BASIN 3 - 0.48 ACRES@ C = 0.78 APPENDIX B 0 5 10 15 20 25 30 35 40 45 50 55 60 Int. (in/hr) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 12.00 12.00 14.00 14.00 Time (min) 100-Yr 50-Yr 25-Yr 10-Yr 5-Yr 2-Yr IDF file: COB IDF.IDF Express Hydraflow IDF Curves Hydraflow IDF Report Page 1 of 1 Return Equation Coefficients (FHA) Period (Yrs) B D E (N/A) 1 0.0000 0.0000 0.0000 -------- 2 4.1995 0.0000 0.6000 -------- 3 0.0000 0.0000 0.0000 -------- 5 7.1453 0.0000 0.6400 -------- 10 9.1617 0.0000 0.6500 -------- 25 10.7179 0.0000 0.6400 -------- 50 13.7204 0.0000 0.6600 -------- 100 15.6922 0.0000 0.6700 -------- N:\2605\027\Design Docs\Reports\Storm Drainage\COB IDF.IDF Intensity = B / (Tc + D)^E Return Intensity Values (in/hr) Period (Yrs) 5 min 10 15 20 25 30 35 40 45 50 55 60 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2 1.60 1.05 0.83 0.70 0.61 0.55 0.50 0.46 0.43 0.40 0.38 0.36 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5 2.55 1.64 1.26 1.05 0.91 0.81 0.73 0.67 0.63 0.58 0.55 0.52 10 3.22 2.05 1.58 1.31 1.13 1.00 0.91 0.83 0.77 0.72 0.68 0.64 25 3.83 2.46 1.89 1.58 1.37 1.22 1.10 1.01 0.94 0.88 0.82 0.78 50 4.74 3.00 2.30 1.90 1.64 1.45 1.31 1.20 1.11 1.04 0.97 0.92 100 5.34 3.35 2.56 2.11 1.82 1.61 1.45 1.33 1.22 1.14 1.07 1.01 Tc = time in minutes. Min Tc = 0 APPENDIX C Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Monday, Mar 2 2020 Pre Basin Hydrology (10-yr) Hydrograph type = Rational Peak discharge (cfs) = 0.702 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 3.570 Runoff coeff. (C) = 0.2 Rainfall Inten (in/hr) = 0.983 Tc by FAA (min) = 31 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 1,306 (cuft); 0.030 (acft) 0 10 20 30 40 50 60 70 Q (cfs) 0.00 0.00 0.10 0.10 0.20 0.20 0.30 0.30 0.40 0.40 0.50 0.50 0.60 0.60 0.70 0.70 0.80 0.80 0.90 0.90 1.00 1.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 0.70 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Pre Basin Hydrology (10-yr) Description Flow length (ft) = 470.00 Watercourse slope (%) = 1.50 Runoff coefficient (C) = 0.20 Time of Conc. (min) = 31 Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Post Basin Hydrology (10-yr) - & Detention Pond Sizing (0.64 coeff) Hydrograph type = Rational Peak discharge (cfs) = 6.532 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 3.570 Runoff coeff. (C) = 0.64 Rainfall Inten (in/hr) = 2.859 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 2,351 (cuft); 0.054 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.00 5.00 6.00 6.00 7.00 7.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 6.53 (cfs)Outflow Hyd *Req. Stor = 2,099 (cuft) * * Estimated Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Monday, Mar 2 2020 Post Basin Hydrology (10-yr) - & Detention Pond Sizing (0.76 coeff) Hydrograph type = Rational Peak discharge (cfs) = 7.756 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 3.570 Runoff coeff. (C) = 0.76 Rainfall Inten (in/hr) = 2.859 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 2,792 (cuft); 0.064 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 7.76 (cfs)Outflow Hyd *Req. Stor = 2,540 (cuft) * * Estimated Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 1 - 25 year conveyance Hydrograph type = Rational Peak discharge (cfs) = 2.536 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 1.330 Runoff coeff. (C) = 0.56 Rainfall Inten (in/hr) = 3.405 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 913 (cuft); 0.021 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 2.54 (cfs) Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2 - 25 year conveyance Hydrograph type = Rational Peak discharge (cfs) = 5.072 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 1.960 Runoff coeff. (C) = 0.76 Rainfall Inten (in/hr) = 3.405 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 1,826 (cuft); 0.042 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.00 5.00 6.00 6.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 5.07 (cfs) Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2,3 - 25 year conveyance Hydrograph type = Rational Peak discharge (cfs) = 6.314 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 2.440 Runoff coeff. (C) = 0.76 Rainfall Inten (in/hr) = 3.405 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 2,273 (cuft); 0.052 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.00 5.00 6.00 6.00 7.00 7.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 6.31 (cfs) Hydrology Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2,3,4 - 25 year conveyance Hydrograph type = Rational Peak discharge (cfs) = 10.30 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 4.200 Runoff coeff. (C) = 0.72 Rainfall Inten (in/hr) = 3.405 Tc by User (min) = 6 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 3,707 (cuft); 0.085 (acft) 0 5 10 15 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 12.00 12.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 10.30 (cfs) APPENDIX D Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 1 - Channel Flow (25-yr Storm) Circular Diameter (ft) = 1.00 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.010 Calculations Compute by: Known Q Known Q (cfs) = 2.54 Highlighted Depth (ft) = 0.66 Q (cfs) = 2.536 Area (sqft) = 0.55 Velocity (ft/s) = 4.60 Wetted Perim (ft) = 1.90 Crit Depth, Yc (ft) = 0.69 Top Width (ft) = 0.95 EGL (ft) = 0.99 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) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2 - Channel Flow (25-yr Storm) Circular Diameter (ft) = 1.25 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.011 Calculations Compute by: Known Q Known Q (cfs) = 5.07 Highlighted Depth (ft) = 0.97 Q (cfs) = 5.070 Area (sqft) = 1.02 Velocity (ft/s) = 4.95 Wetted Perim (ft) = 2.70 Crit Depth, Yc (ft) = 0.92 Top Width (ft) = 1.04 EGL (ft) = 1.35 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2, 3 - Channel Flow (25-yr Storm) Circular Diameter (ft) = 1.50 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.011 Calculations Compute by: Known Q Known Q (cfs) = 6.31 Highlighted Depth (ft) = 0.94 Q (cfs) = 6.310 Area (sqft) = 1.17 Velocity (ft/s) = 5.40 Wetted Perim (ft) = 2.74 Crit Depth, Yc (ft) = 0.98 Top Width (ft) = 1.45 EGL (ft) = 1.39 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Mar 3 2020 Basin 2, 3, 4 - Channel Flow (25-yr Storm) Circular Diameter (ft) = 1.75 Invert Elev (ft) = 100.00 Slope (%) = 0.30 N-Value = 0.011 Calculations Compute by: Known Q Known Q (cfs) = 10.30 Highlighted Depth (ft) = 1.45 Q (cfs) = 10.30 Area (sqft) = 2.13 Velocity (ft/s) = 4.83 Wetted Perim (ft) = 4.01 Crit Depth, Yc (ft) = 1.20 Top Width (ft) = 1.32 EGL (ft) = 1.81 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft)