Water Resources and Environmental Engineering

The mean velocity (or discharge) of steady, uniform flow in an open channel as a function of roughness, hydraulic radius, and channel slope.

V = (1/n) R^(2/3) S^(1/2), where n is roughness, R is hydraulic radius (m), and S is the channel slope.

1.486 — so V = (1.486/n) R^(2/3) S^(1/2) with R in feet and V in ft/s.

R = A/P, the cross-sectional flow area A divided by the wetted perimeter P.

R = D/4, since A = πD²/4 and P = πD.

The depth at which uniform flow occurs for a given discharge, slope, roughness, and channel shape — where the water surface is parallel to the channel bottom.