Free Online Manning 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):

1. What is Manning's Equation Calculator?

Definition: This calculator estimates the flow rate in open channels or pipes using Manning's equation, which relates flow velocity to channel geometry and roughness.

Purpose: It helps engineers, hydrologists, and water resource professionals design and analyze open channel flow systems.

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 (dimensionless)
\( A \) — Cross-sectional area of flow (m²)
\( R \) — Hydraulic radius (m) = A/P (P is wetted perimeter)
\( S \) — Slope of the energy grade line (dimensionless)

Explanation: The equation calculates flow rate based on channel characteristics and roughness.

3. Importance of Manning's Equation

Details: Proper flow rate estimation ensures adequate drainage, proper pipe sizing, and efficient water conveyance system design.

4. Using the Calculator

Tips: Enter Manning's roughness coefficient (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: Common values: 0.013 (concrete), 0.015 (clay), 0.022 (gravel), 0.03 (natural streams).

Q2: How do I calculate hydraulic radius?
A: R = A/P where A is cross-sectional area and P is wetted perimeter. For full circular pipe: R = D/4.

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

Q4: Can this be used for pressurized pipes?
A: Manning's equation is primarily for open channel flow, but can approximate partially full pipe flow.

Q5: How accurate is Manning's equation?
A: It's an empirical equation accurate for steady, uniform flow conditions in rough channels.