Batch discharge scenarios
Enter one line per scenario: discharge, bottom width, left H:V, right H:V, slope, Manning n.
| # | Discharge | Bottom width | Left slope | Right slope | Bed slope | Manning n | Normal depth | Velocity | Status |
|---|
Formula used
Area: A = by + ½(zL + zR)y²
Wetted perimeter: P = b + y√(1 + zL²) + y√(1 + zR²)
Hydraulic radius: R = A/P
Top width: T = b + (zL + zR)y
Manning equation: Q = (k/n)AR2/3S1/2
Use k = 1.0 for metric units. Use k = 1.486 for US customary units.
How to use
- Select the value that the calculator should solve.
- Choose one consistent measurement system for all inputs.
- Enter discharge, geometry, slope, and surface roughness.
- Add channel depth and velocity limits for safety checks.
- Calculate and review warnings before using any design.
Example data
| Parameter | Metric example | US customary example |
|---|---|---|
| Discharge | 5 m³/s | 176.57 ft³/s |
| Bottom width | 3 m | 9.84 ft |
| Side slopes | 2H:1V | 2H:1V |
| Bed slope | 0.001 | 0.001 |
| Manning n | 0.015 | 0.015 |
| Total depth | 2 m | 6.56 ft |
| Required freeboard | 0.30 m | 0.98 ft |
Manning roughness reference
| Channel surface | Typical n range | Design note |
|---|---|---|
| Finished concrete | 0.011–0.014 | Smooth, aligned surfaces. |
| Unfinished concrete | 0.014–0.020 | Joints and surface irregularities matter. |
| Earth channel | 0.020–0.035 | Condition and maintenance change roughness. |
| Gravel channel | 0.025–0.040 | Particle size affects resistance. |
| Vegetated channel | 0.030–0.100 | Seasonal growth can change capacity. |
| Natural stream | 0.030–0.150 | Use field judgement and calibration. |
Frequently asked questions
What is normal depth?
Normal depth is the uniform-flow depth for fixed discharge, geometry, slope, and roughness.
Why is an iterative solver required?
Depth appears inside both area and hydraulic radius. Direct isolation is usually unavailable.
Can the channel sides be different?
Yes. Enter separate left and right slopes for an asymmetrical trapezoidal channel.
What does Froude number show?
It compares flow inertia with gravity effects. It identifies subcritical or supercritical flow.
How is critical depth calculated?
The calculator solves the critical-flow condition using the selected discharge and section geometry.
What is composite roughness?
Composite roughness estimates one effective value from different side and bottom lining materials.
Why is freeboard important?
Freeboard provides space for waves, uncertainty, debris, sediment, and temporary flow increases.
Can this replace a hydraulic model?
No. Complex transitions, backwater, controls, and unsteady flow need detailed hydraulic modelling.
Which Manning value should be used?
Choose a value matching actual material, condition, vegetation, alignment, and maintenance quality.