Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

PART II:Routing Excess Runoff through a Vegetative Swale(Use peak hydraulic flows on the site.)Q = Peak hydraulic flow rate(For Sacramento area projects, use Figure 2-5 Design Runoff Nolte Method from Section 9 of Countyof Sacramento Municipal Services Agency Improvement Standards October 1, 2006 to find Q.)Q = 1.5 cfs (Swale #1 treating a 3 acre site)To determine the capacity of the swale to convey peak hydraulic flows, use a roughnesscoefficient (n) of 0.10 with Manning’s Equation.Q = (1.49/n) (by + Zy 2 ) [ ( by + Zy 2 ) / (b + 2y√ (1 + Z 2 ))] 2/3 (s) 1/2 (eqn 3)1.5 = (1.49/.1) (5y + 3y 2 ) [(5y + 3y 2 ) / (5 + 2y√10)] 2/3 (.01) ½(Using the solver function: y 2 = .365 ft.)y 2 = Depth of peak drainage flow = 0.365 ft.