Culvert Flow Calculator

How to Use the Calculator

1. Select the type of culvert from the dropdown menu (Box, Arch, or Circular Pipe).
2. Enter the width of the culvert in meters.
3. Enter the height of the culvert in meters.
4. Enter the headwater depth in meters (the vertical distance from the culvert invert to the water surface).
5. (Optional) Adjust the Manning's roughness coefficient. The default value (0.013) is suitable for concrete culverts.
6. Click the "Calculate" button to compute the flow rate, velocity, and cross-sectional area.

Understanding the Results

The calculator provides three key results:

• Flow Rate (m³/s): The volume of water passing through the culvert per second.
• Velocity (m/s): The speed at which water flows through the culvert.
• Cross-sectional Area (m²): The area of the culvert opening.

Principles of the Calculation

The calculator uses Manning's equation to estimate the flow velocity in open channels:

Velocity (V) = (1/n) × R^2/3 × S^1/2

Where:

• V = Velocity (m/s)
• n = Manning's roughness coefficient
• R = Hydraulic radius (m)
• S = Slope of the energy line (assumed equal to the slope of the culvert invert)

The flow rate (Q) is then calculated as:

Q = A × V

Where:

• Q = Flow Rate (m³/s)
• A = Cross-sectional Area (m²)
• V = Velocity (m/s)

Applications

This calculator is useful for:

• Designing drainage systems and culverts for roads, bridges, and other infrastructure.
• Assessing the capacity of existing culverts to handle flood flows.
• Planning water resource management projects.