Gravity Drain Flow Rate Calculator

Manning's Equation:

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

Manning's Roughness Coefficient (n):

Cross-sectional Area (A):

m²

Hydraulic Radius (R):

Slope (S):

Flow Rate (Q):

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

Purpose: It helps civil engineers, hydrologists, and drainage designers calculate water flow in gravity-fed systems.

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 rate.

Details: Accurate flow rate estimation ensures proper drainage system design, prevents flooding, and optimizes channel dimensions.

Tips:

Q1: What are typical Manning's n values?
A: 0.012-0.015 for smooth concrete, 0.022-0.030 for natural streams, 0.025-0.035 for vegetated channels.

Q2: How do I calculate hydraulic radius?
A: Divide the cross-sectional area by the wetted perimeter (length of channel in contact with water).

Q3: What units should the slope be in?
A: The slope is dimensionless (m/m or ft/ft), representing the vertical drop per unit horizontal distance.

Q4: Can this be used for pressurized pipes?
A: No, Manning's equation is for open channel flow only. Use Darcy-Weisbach for pressurized pipes.

Q5: How accurate is Manning's equation?
A: It's empirically derived and generally accurate within 10-20% for uniform, steady flow conditions.