Open-Channel Flow

Manning's equation — rectangular, trapezoidal, triangular & circular channels; velocity, discharge, Froude.

US customary units (ft, ft/s, cfs). Manning's n and the channel slope come from the channel design / Chow's roughness tables. Uniform (normal) flow is assumed.

Design diagram — updates live with your inputs

Channel Section

Channel shapei

Bottom width b (ft)i Base width (0 for triangular)

Side slope z (H:V)i Horizontal run per vertical rise

Pipe diameter (ft)i Circular section only

Flow depth y (ft)i

Roughness & Slope

Manning's ni Channel roughness

Channel slope S (ft/ft)i Bed slope (rise/run)

Check

Design flow (cfs)i Optional — checks demand vs capacity

US customary (ft, cfs)

Validation, assumptions & limitations Download validation report (PDF) ↗

This calculator is verified by 4 independent tests comparing its output against closed-form statics, NDS/SDPWS design-standard values and published worked examples. Full case-by-case results are in the PDF report.

Assumptions

Uniform (normal) steady flow; US customary units (k = 1.49).
Manning's n is the channel roughness (Chow's tables) - an input.
Prismatic channel, hydrostatic pressure distribution.

Limitations

n and the slope S are design inputs; results scale strongly with both.
Normal flow only - not gradually/rapidly varied flow profiles.
Circular section assumes part-full; check the part-full curve near full.

Results are for preliminary design and must be confirmed by a licensed engineer against the current adopted code and project-specific conditions.