What is a culvert?
A culvert is a pipe, box or short tunnel that carries water beneath a road, embankment, path or building so that the infrastructure above is not interrupted. It provides a flow connection between two watercourses or carries rain and groundwater away, and is an essential element in water management.
How does a culvert work?
A culvert is a closed conduit installed underground. The shape can be circular, oval, rectangular or arch-shaped. The inlet and outlet are usually finished with a concrete headwall or a grille.
Key design points:
- Cross-section — large enough that even peak flows do not cause backwater
- Material — concrete, cast iron, steel or plastic, depending on size and load
- Gradient — a slight fall promotes self-cleaning
- Connection — a smooth transition to the watercourse prevents scour
- Wing walls — masonry or concrete at inlet and outlet protect against erosion
Application
- Under roads — crossing ditches and streams
- Under embankments — water passage with optional flap valves
- On farmland — accessible crossings over ditches
- At railways — to carry streams beneath the line
- In urban areas — beneath squares, parks and paths
Points of attention
- Size the capacity for the whole catchment area
- Maintain enough cover above the culvert
- Provide trash screens but clean them regularly
- Coordinate levels with the water authority’s regulated levels
- Maintenance is essential — a blocked culvert causes flooding
Related terms
- Drainage
- Sewerage
- Bridge
- Building plot
- Sheet piling
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