Given: Pavement consists of two 10 ft. lanes with a vertical curb. SL = 2% ST = 2%. Two-foot gutter. Permissible spread on pavement 6 ft.

Step 1

Spread: 6 + 2 = 8 ft.
Depth at curb = 8 x .02 = .016 ft.
Discharge for depth at curb Q = (.56 / N) Z (D 8/3) S 1/2 Solving equation by calculator Q = 1.9 cfs

Step 2

Determine capacity and spacing of the first inlet on the slope. Pavement area which will produce equivalent discharge from the equation: Q = CIA
Assume C = 0.9 and I = 4″/HR.
A = (Q / IC) = (1.85 / (4 x 0.9)) = 0.51 acres
Length to first inlet L = A / W = (.051 x 43560) / 22 = 1010 ft.

Step 3

Using Neenah inlet R-3246-A, Type C, K = 26
Substituting in the formula Q = K D5/3
Q = 26 x (.16)5/3 = 26 x .047 = 1.226 CFS
By-pass 1.85 – 1.23 = 0.62 CFS

Step 4

Length to next inlet: Q / ICW = (1.23 x 43560) / (4 x 0.9 x 22) = 676 ft.

Solution

Station Q Gutter Depth Gutter Q Grate Q Bypass Spread on Pavement
10 + 10 1.85 cfs 0.16′ 1.23 cfs 0.62 cfs 6.0′ + 2′ gutter
10 + 60 0.62+ cfs 0.11′ N/A N/A 3.5′ + 2′ gutter
16 + 86 1.85 cfs 0.16′ 1.23 cfs 0.62 cfs 6.0′ + 2′ gutter
23 + 62 1.85 cfs 0.16′ 1.23 cfs 0.62 cfs 6.0′ + 2′ gutter

For additional information regarding Neenah Inlet Grate Capacities, please contact Product engineering @ engineering@neenahenterprises.com