Open-channel flow (Manning)

Steady uniform (normal) flow in circular, trapezoidal, or rectangular channels — solves discharge from a known depth, or normal depth from a known discharge, plus Froude-number flow-regime classification.

Manning's equation (Chow 1959) with the SI unit constant k=1.0 fixed internally (the US value 1.486 is presentation-only and never substituted). Circular sections use the exact central-angle geometry and bisect on the monotone rising limb (y/D≤0.938) since conveyance is non-monotonic near the crown.