Pipe Capacity Manning's Equation Calculator

Manning's Formula:

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

Roughness Coefficient (n):

Cross-sectional Area (A):

m²

Hydraulic Radius (R):

Slope (S):

Flow Rate (Q):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Manning's Equation?

Manning's equation is an empirical formula used to calculate the flow rate in open channels and pipes. It relates the flow rate to the channel's cross-sectional area, hydraulic radius, slope, and roughness coefficient.

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 of flow (m²)
\( R \) — Hydraulic radius (m)
\( S \) — Slope of the energy grade line (-)

Explanation: The equation calculates the volumetric flow rate based on the channel geometry and flow characteristics.

3. Importance of Flow Rate Calculation

Details: Accurate flow rate calculation is essential for designing drainage systems, irrigation channels, sewer systems, and various hydraulic engineering applications.

4. Using the Calculator

Tips: Enter Manning's roughness coefficient, cross-sectional area, hydraulic radius, and slope. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for Manning's roughness coefficient?
A: Typical values range from 0.010 for smooth surfaces to 0.060 for very rough channels. Concrete pipes typically have n = 0.012-0.015.

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

Q3: What units should be used for slope?
A: Slope should be entered as a dimensionless ratio (vertical drop/horizontal distance).

Q4: When is Manning's equation applicable?
A: Manning's equation is applicable for steady, uniform flow in open channels and partially full pipes.

Q5: Are there limitations to Manning's equation?
A: The equation is empirical and may not be accurate for very steep slopes, rapidly varying flow, or non-uniform channel sections.