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Manning's Open Channel Flow

Compute open-channel flow using Manning's equation. Solve for discharge, normal depth or required slope across rectangular, trapezoidal, triangular and circular sections — live cross-section diagram.

Inputs

Units

Solve For

Section

Manning's n

n value

Discharge Qm³/s

Slope S (m/m or ft/ft)e.g. 0.001 = 0.1%

Notes & assumptions

Manning's: V = (1/n)·R^(2/3)·S^(1/2). Imperial uses 1.486/n.
R = A/P (hydraulic radius). Normal depth solver uses bisection.
Circular: input diameter D and depth y (must be ≤ D).
Critical depth, Froude number and flow regime are reported.

Results

Discharge Q—

Velocity V—

Depth y—

Flow Area A—

Wetted Perimeter P—

Hydraulic Radius R—

Top Width T—

Slope S—

Froude Fr—

Flow Regimesubcritical