Calculator Inputs
Example Data Table
Example values for a lined trapezoidal canal using Manning method.
| Shape | y | b | z | S | n | Computed Q |
|---|---|---|---|---|---|---|
| Trapezoidal | 1.20 m | 2.50 m | 1.50 | 0.0015 | 0.015 | ≈ 7.0 m³/s |
| Rectangular | 0.80 m | 1.80 m | — | 0.0020 | 0.014 | ≈ 3.2 m³/s |
| Circular (partial) | 0.60 m | — | — | 0.0010 | 0.013 | ≈ 1.1 m³/s |
Values are illustrative; verify roughness and slope on site.
Formula Used
Manning method
Q = (1/n) · A · R^(2/3) · S^(1/2)
- Q = discharge (flow rate)
- A = wetted cross‑sectional area
- P = wetted perimeter
- R = hydraulic radius, R = A / P
- S = bed slope (energy slope approximation)
- n = roughness coefficient
Chezy method
V = C · √(R · S) and Q = A · V
Use when a calibrated Chezy coefficient is available for the canal lining.
Velocity–Area method
Q = A · V
Use when velocity is measured or specified from operations.
How to Use This Calculator
- Select the unit system that matches your field measurements.
- Choose a channel shape and enter the flow depth.
- Provide the geometric parameters for the selected shape.
- Select a method: Manning, Chezy, or Velocity–Area.
- Enter bed slope and the required coefficient values.
- Click Calculate to view the discharge above the form.
- Export results using the CSV or PDF buttons.
Accurate inputs create reliable flow estimates for projects today.