Gravity Pipe Flow Calculator

Manning's Equation:

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

Manning's Roughness (n):

Cross-sectional Area (A):

m²

Hydraulic Radius (R):

Slope (S):

Flow Rate (Q): m³/s

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

Purpose: It helps engineers, hydrologists, and planners design and analyze drainage systems, sewers, and natural channels.

The calculator uses Manning's equation:

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

Where:

Explanation: The equation accounts for channel roughness, geometry, and slope to determine flow capacity.

Details: Accurate flow estimation ensures proper drainage system design, flood prevention, and efficient water conveyance.

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

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

Q2: How is hydraulic radius calculated?
A: R = A/P where P is wetted perimeter. For full circular pipe: R = D/4.

Q3: What units should slope be in?
A: Enter as dimensionless ratio (e.g., 0.01 for 1% slope).

Q4: When is Manning's equation valid?
A: For steady, uniform flow in open channels or partially full pipes.

Q5: How accurate is this calculation?
A: Accuracy depends on correct parameter selection, especially roughness coefficient.