Open channels
Uniform flow in any cross-section, divided where its roughness changes: normal depth by Manning, critical depth, Froude number and bank-full capacity.
The open channel tool calculates steady, uniform flow in a prismatic channel of any cross-section: normal and critical depth, velocity, Froude number, specific energy, and whether the discharge fits below the banks. Gradually varied flow (backwater profiles), unsteady flow, culverts, weirs and sediment transport are outside it.
What it checks
| Check | Rule | Limit |
|---|---|---|
Bank-full capacity The discharge fits below the lower bank |
There is no factor of safety: the one check is whether the discharge fits, and its limit, the bank-full capacity, comes from the section itself.
How a model is built
A model is one cross-section, its longitudinal slope and the discharge . The section is drawn vertex by vertex, from bank to bank, and each segment has its own Manning ; the first and last vertices are the banks, both higher than the bed.
In these pages
- Inputs: the section, the slope and the discharge, field by field.
- Method and assumptions: the units and conventions, what the calculation assumes, and its method in order.
- Section and roughness: the section at a water level, and the parts it divides into where its roughness changes.
- Normal and critical flow: normal depth by Manning, critical depth, Froude number and specific energy.
- Capacity and rating curve: what the section carries with the water at its lower bank, and at each level below it.
- Equations: every step of the calculation, in the order of the calculation report.
- Warnings: what each warning means.