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HomeMy WebLinkAbout16 - Design Report - Egbert Electric & Plumbing Site - Stormwater DESIGN REPORT STORMWATER MANAGEMENT EGBERT ELECTRIC & PLUMBING SITE Prepared for: Meadowlark Rentals, LLC P.O. Box 4314 Bozeman, MT 59771 Prepared by: C&H Engineering and Surveying, Inc. 1091 Stoneridge Drive Bozeman, MT 59718 (406) 587-1115 Project Number: 16260 July 2016 INTRODUCTION The proposed Egbert Electric Fz Plumbing project is located on Tract C of the plat recorded in Book 135 of Deed, Page 492. The lot is 1.45 acres.The project is located in Bozeman, Montana at 875 Bridger Drive. RETENTION POND DESIGN Retention ponds have been sized according to City of Bozeman Design Standards and are sized to capture the entire volume of the 10-year 2-hour storm event. Stormwater runoff from the project will be conveyed to two retention facilities —Retention Pond 41 on the south side of the site and Retention Pond #2 on the north side of the site. Drainage Area #1 will discharge into Retention Pond#1 at the south side of the site.Drainage Area#2 will discharge into Retention Pond#2 at the north side of the site. Runoff will sheet flow from across the parking lot and will enter the ponds through curb cuts at the perimeter of the parking lot. Water will be retained in the ponds where it will infiltrate and evaporate.A drainage area map is included in Appendix A. Calculations for each individual drainage area (contributing area, weighted C factor, and time to concentration) are included in Appendix B. Retention Pond #1 Retention Pond#1 is located on the south side of the site.It receives runoff from Drainage Area#1, totaling 0.80 acres. The required pond volume was calculated to be 1766 cubic feet. The proposed pond design has a volume of 1850 cubic feet. In the case of a storm exceeding the 10-yr 2-hour design stone, runoff will pond on the south side of the parking lot until it overflows across the property to the west and onto Birdie Drive. From there it will enter the City of Bozeman storm drainage system which eventually outlets into the East Gallatin River. Retention Pond #2 Retention Pond#2 is located on the north side of the site.It receives runoff from Drainage Area#2, totaling 0.70 acres. The required pond volume was calculated to be 1669 cubic feet. The proposed Design.Report-Page 2 of 5 pond design has a volume of 1890 cubic feet. In the case of a storm exceeding the 10-yr 2-hour design storm, runoff will overflow onto the property to the north, as is the current situation, eventually flowing onto Birdie Drive. From there it will enter the City of Bozeman storm drainage system which eventually outlets into the East Gallatin River. Design Report-Page 3 of S APPENDIX A DRAINAGE AREA MAP Design Report-Page 4 of 5 D1RA/IGWE ARE4 E UMT EGBERT ELECTRIC & PLUMBING SITE 845 BRIDGER DRIVE, BOZEMAN, MONTANA LEGEND 7 ROOF LANDSCAPE HARDSCAPE R-3 ZONING 206.4 (R) [S89.33.5t E] 207.21 091728'08" (M) ncr j --s un r LOT 2 %/• / / -� to F LOT 3 4OF , }43F ry _ GAS - - CAW _ Ft I%6..O0 3RDGER CAM'0N M- k Scale In Feet 40 0 40 12 0 12 R-2 ZONVIAG `_ --- -- — — Scale In Meters - Contour Intervals: f Foot r Engineering and Surveying Inc. 1091 6caneridge 06v.•9azemen.MT 59718 Phone(406)587.1115•Fex(406)587-9768 www chengioe¢rs •inloochengineers.wm Sheet I of 1 #16260 APPENDIX B DRAINAGE AREA AND POND SIZING CALULATIONS Design Report-Page 5 of 5 PRE-DEVELOPMENT RUNOFF 1. Calculate Tc(Pre-Development) Tc Overland Flow Tc= 1.87 (1.1-CC)D'/2/S,i3 ----------------------------- 'Storm S=Slope of Basin (%} 1.5 I'Return (yrs Cf C= Rational Method Runoff Coefficient 0.2 ,2 to 10 1 Cf= Frequency Adjustment Factor 1.1 1 11 to 25 1.1 D= Length of Basin (ft) 230 ;26 to 50 1.2 151 to 100 1.25 Tc(Pre-Development) (minutes) 22 2. Calculate Rainfall intensity(Duration=Pre-Development Tc) i=0.64x os5 (10-yr Storm, Fig. 1-3, COB Design Standards) x=storm duration(hrs) 0.36 (Tc Pre-Development) i=rainfall intensity(inJhr.) 1.24 3. Calculate Runoff Rate(Pre-Development) Q = CiA C = Rational Method Runoff Coefficient 0.2 (open land) i = rainfall intensity(in./hr.) 1.24 (calculated above) A=Area(acres) 1.45 Q=Runoff Rate (Pre-Development)(cfs) 0.36 RETENTION POND # 1 REQUIRED VOLUME 9. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C*Area Hardscape 0.95 20800 19760 Landscape 0.2 9663 1933 Roof 095 4593 4363 Total 36066 26066 C=Weighted C Factor 0.74 3. Calculate Required Volume Q =CIA V=7200Q C =Weighted C Factor 0.74' 1 = intensity(in/hr) 0A1 (10 yr, 2hr storm) A=Area(acres) 0.80 Q = runoff(cfs) 0:25 V= REQUIRED VOL(ft) 1766 RETENTION POND# 2 REQUIRED VOLUME 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 16147 15339 Landscape 0.2 5804 1161 Roof 095 8551 8124 Total 30602 24624 C=Weighted C Factor (181 3. Calculate Required Volume Q =CIA V=7200Q C=Weighted C Factor 081 1 = intensity(in/hr) 0.41 (10 yr, 2hr storm) A=Area(acres) Q70 Q =runoff(cfs) 023' V= REQUIRED VOL(ft) 1669'