3003 W CASINO RD BLDG 45-05 2025-04-14

i Drainage Memo Boeing Flightline, Building 45-005 Swale March 25, 2020 Page 3 PIPE SIZING: All pipes will be sized for the 25-year, 24-hour event using the Manning's formula for open channel flow and checked for the 100-year, 24-hour storm. 25 YEAR CALCULATION Manning's Coef, n = 0.012 Conc Pipe Diameter, D = 6.0 inches Slope = 0.0017 ft/ft Depth of Flow, h = 6.0 inches Results (assumes constant n): Full Pipe Area, A= 0.2 sq ft Flow Area, a = 0.2 sq ft Wetted Perimeter, P = 1.6 feet Hydraulic Radius, R = 0.1 feet Q full = 0.25 cfs V full = 1.28 fps Design for 25-year storm: @ depth = 7 inches, V = 1.28 fps @ depth = 7 inches, Q = 0.25 _ cfs OK 100 YEAR CALCULATION Manning's Coef, n = 0.012 Conc Pipe Diameter, D = 6.0 inches Slope = 0.0017 ft/ft Depth of Flow, h = .0 inches Results (assumes constant n): Full Pipe Area, A= 0.2 sq ft Flow Area, a = 0.2 sq ft Wetted Perimeter, P = 1.6 feet Hydraulic Radius, R = 0.1 feet Q full = 0.25 cfs V full = 1.28 fps Check for a 100-year storm: @ depth = 7 inches, V = 1.28 fps @ depth = 7 inches, Q = 0.25 cfs OK CONCLUSION For simplicity, the swale was modeled conservatively modeled as a 6" pipe at 0.17% slope (the swale slope). The calculations above show that a 6" pipe is a minimum size needed to convey the storm runoff for the contributing area. Approximately 1 square foot (6" depth by 2' width)of an opening under the building is being provided at a 0.17% slope. The cross-section required needs to be a minimum of 0.196 square feet, therefore the 1 square-foot opening with the 0.17% slope is adequate for the conveyance requirements. www.coffman.com