Open Channel Flow Calculator
Rectangular channel using Manning equation: Q = (1/n) · A · R^0.6666666666666666 · S^0.5.
Typical n: finished concrete 0.012–0.016, earth 0.020–0.035.
How to Use This Calculator
Provide channel geometry
Enter rectangular width b and depth y in meters.
Enter hydraulic parameters
Input bed slope S (dimensionless) and Manning n based on surface roughness.
Calculate discharge
Press Calculate to obtain Q, A, P, and R for your channel.
Formula
Q = (1/n) · A · R^0.6666666666666666 · S^0.5
Where: Q is discharge (m³/s), n is Manning roughness, A is area (m²), R is hydraulic radius (m), S is slope.
Rectangular channel: A = b·y, P = b + 2y, R = A/P.
Example: b=3 m, y=1.2 m, S=0.001, n=0.015 ⇒ A=3.6 m², P=5.4 m, R=0.6667 m, Q≈ 5.792 m³/s.
About Open Channel Flow Calculator
This tool estimates steady, uniform open-channel discharge using the Manning equation for a rectangular cross-section. It assists in preliminary hydraulic design and analysis.
When to Use This Calculator
- Drainage design: Size channels and ditches.
- Irrigation canals: Evaluate capacity for given depth.
- Waterways: Assess effects of slope and roughness.
Why Use Our Calculator?
- ✅ Immediate: Computes Q along with A, P, and R.
- ✅ Practical: Uses standard Manning relation and typical n guidance.
- ✅ User-friendly: Minimal inputs with clear outputs.
Frequently Asked Questions
Which roughness n should I pick?
Consult standard tables (e.g., Chow or ASCE) for materials and conditions. Smooth concrete ~0.012–0.016; natural earth channels ~0.020–0.035.
Does this handle non-rectangular sections?
This version assumes a rectangular section. For trapezoidal or circular sections, A, P, and R formulas differ.
Is the result valid for rapidly varied flow?
No. Manning equation is for steady, uniform flow. Rapidly varied or non-uniform flow requires more advanced analysis.