Trapezoidal Channel Capacity Calculator

Manning's Formula:

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

Manning's Coefficient (n):

dimensionless

Cross-sectional Area (A):

m²

Hydraulic Radius (R):

Slope (S):

dimensionless

Flow Capacity (Q):

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1. What is Manning's Formula?

Manning's formula is an empirical equation used to calculate the flow capacity in open channels. It relates the flow rate to the channel's cross-sectional properties, slope, and roughness characteristics.

2. How Does the Calculator Work?

The calculator uses Manning's formula:

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

Where:

\( Q \) — Flow capacity (m³/s)
\( n \) — Manning's roughness coefficient (dimensionless)
\( A \) — Cross-sectional area of flow (m²)
\( R \) — Hydraulic radius (m)
\( S \) — Channel slope (dimensionless)

Explanation: The formula calculates the volumetric flow rate through an open channel based on its geometric properties and surface roughness.

3. Importance of Flow Capacity Calculation

Details: Accurate flow capacity calculation is crucial for hydraulic engineering, drainage design, irrigation systems, and flood management in trapezoidal channels.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What are typical Manning's coefficient values?
A: Values range from 0.012 (smooth concrete) to 0.035 (natural streams with vegetation). Consult engineering tables for specific materials.

Q2: How is hydraulic radius calculated?
A: Hydraulic radius = Cross-sectional area / Wetted perimeter. For trapezoidal channels, this requires knowing bottom width, side slopes, and flow depth.

Q3: What units should be used?
A: Use metric units: area in m², hydraulic radius in m, and slope as a dimensionless ratio (e.g., 0.001 for 0.1% slope).

Q4: When is Manning's formula applicable?
A: For steady, uniform flow in open channels with constant cross-section and slope. Not suitable for pressurized flow or rapidly varied flow conditions.

Q5: What are the limitations of Manning's formula?
A: Accuracy depends on proper selection of Manning's n value. The formula assumes turbulent flow and may not be accurate for very smooth surfaces or low velocities.