Complete Guide to Open Channel Flow
The Channel Flow Calculator uses Manning’s equation to determine discharge, velocity, or normal depth. Essential for drainage, irrigation, and flood control. Pair with Stormwater Runoff and Hydraulic Jump tools.
Manning’s Equation
\( Q = \frac{1}{n} A R^{2/3} S^{1/2} \)
\( V = \frac{1}{n} R^{2/3} S^{1/2} \)
Why Calculate?
- Capacity: Avoid overflow
- Velocity: Prevent erosion/scour
- Design: Size channels
Section Properties
| Section | A | P | R = A/P |
|---|---|---|---|
| Rectangular | by | b+2y | by/(b+2y) |
| Trapezoidal | (b+zy)y | b+2y√(1+z²) | A/P |
| Triangular | zy² | 2y√(1+z²) | zy/2√(1+z²) |
Step-by-Step
- Select section
- Input geometry, n, S
- Compute A, R, Q or yn
Example: Trapezoidal
b=2m, z=2, y=1.5m, n=0.015, S=0.001:
- A = 7.5 m²
- R = 0.88 m
- Q = 12.1 m³/s
Typical n Values
| Surface | n |
|---|---|
| Concrete (smooth) | 0.012–0.015 |
| Earth (clean) | 0.022 |
| Grass | 0.030–0.040 |
Applications
- Irrigation canals
- Storm drains
- River training
Best Practices
- Use 1.5–2:1 side slopes
- Limit V < 1.5 m/s (erosion)
- Provide freeboard (0.3–0.5m)
Common Mistakes
- Wrong n value
- Ignoring velocity limits
- No freeboard
Advanced Topics
- Gradually varied flow
- Critical depth
- HEC-RAS modeling
Conclusion
Accurate channel design prevents flooding and erosion. Our Channel Flow Calculator delivers instant hydraulic parameters. Integrate with Runoff for full stormwater systems. Design efficient, safe channels!