Culvert Design Calculator
Estimate velocity, hydraulic radius, and cross-sectional area from culvert diameter and design flow values.
Design Inputs
Provide the culvert diameter and the expected flow rate to compute hydraulic metrics.
How to Use This Calculator
Enter the culvert diameter and your design flow rate. The calculator applies the Hydraulic Design Series approach from the FHWA to estimate velocity and hydraulic radius, helping you verify hydraulic capacity and check for potential scour concerns.
Methodology
Hydraulic radius is computed as one-quarter of the culvert diameter for a full circular section. Velocity follows the continuity equation Q = A × V, where the cross-sectional area derives from π × (diameter / 2)2.
Data & Sources
This tool depends on the Hydraulic Design Series from the Federal Highway Administration and supporting calculations documented by LMNO Engineering.
Glossary
- Culvert Diameter: The internal width of the culvert pipe.
- Flow Rate (Q): Volume of water passing through the culvert per second (m³/s).
- Hydraulic Radius (R): Cross-sectional area divided by wetted perimeter; for full circular sections it equals diameter / 4.
- Velocity (V): The speed of flow required to pass the design discharge.
Practical Example
A 2 m culvert carrying 1.5 m³/s results in 0.5 m hydraulic radius and about 0.48 m/s velocity, which helps gauge whether the culvert can convey the flood event without exceeding erosive velocities.
FAQ
What is a culvert?
A culvert allows water to pass under roadways, railways, or embankments.
Why is hydraulic radius important?
It relates flow area to wetted perimeter and informs resistance coefficients.
How is velocity calculated?
Velocity is flow rate divided by cross-sectional area.
How can I use the results?
Compare velocities against allowable limits and confirm hydraulic radius for sizing.