Rectangular Open Ditch (Non-Full)

Non-full flow in a rectangular open ditch. X = W + 2H, A = W·H, R = A/X, v = R^(2/3)·√i/n, Q = A·v.

Inputs

Channel width W m

Water depth H m

Roughness n —

Hydraulic gradient i —

Result

Velocity v

—

m/s

Flow rate Q

—

m³/s

Flow area A

—

m²

Wetted perimeter X

—

Hydraulic radius R

—

X = W + 2H, A = W·H, R = A/X. Manning velocity v = (R^(2/3)·√i)/n with n default 0.013; discharge Q = A·v. Enter W, H and i (as a fraction) to trial the flow and velocity.