Hi unclejonsson

This post belongs in other topics.Formula for mean velocity V = 1.5 R^2/3*s^1/2 Divided by n (ft sec units)

R = hydraulic radius (area of shaded area at head end)/( wetted perimeter)

s is gradient ft per ft of length

n is a roughness factor

Area 1.84 sq ft,wetted perimeter 3.47 ft,s= .012. n = .012 smooth surface

V=8.9 fps Q= VA = 8.9 *1,84= 16.4 cfs