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Manning Pipe Flow Calculator

Manning's Equation:

\[ Q = \frac{1}{n} \times A \times R^{\frac{2}{3}} \times S^{\frac{1}{2}} \]

m²
m
m³/s

1. What is the Manning Pipe Flow Calculator?

Definition: This calculator estimates the flow rate in open channels or pipes using Manning's equation.

Purpose: It helps engineers, hydrologists, and water resource professionals calculate water flow in various channel types.

2. How Does the Calculator Work?

The calculator uses Manning's equation:

\[ Q = \frac{1}{n} \times A \times R^{\frac{2}{3}} \times S^{\frac{1}{2}} \]

Where:

  • \( Q \) — Flow rate (m³/s)
  • \( n \) — Manning's roughness coefficient
  • \( A \) — Cross-sectional area (m²)
  • \( R \) — Hydraulic radius (m)
  • \( S \) — Slope (dimensionless, m/m)

Explanation: The equation relates flow velocity to channel characteristics and slope.

3. Importance of Manning's Equation

Details: Accurate flow rate calculations are essential for designing drainage systems, irrigation channels, and flood control structures.

4. Using the Calculator

Tips: Enter Manning's n (default 0.013 for concrete pipes), cross-sectional area, hydraulic radius, and slope. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What are typical Manning's n values?
A: 0.013 for concrete, 0.015 for PVC, 0.03 for natural streams, 0.035-0.05 for vegetated channels.

Q2: How is hydraulic radius calculated?
A: R = A/P where A is cross-sectional area and P is wetted perimeter.

Q3: What units should slope be in?
A: Slope is dimensionless (m/m), so 1% slope = 0.01.

Q4: Can this be used for full pipe flow?
A: Yes, but hydraulic radius must be calculated for full pipe conditions.

Q5: What's the accuracy of Manning's equation?
A: Generally ±10-20% for uniform flow in prismatic channels.

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