What is culverting?
Culverting — also called decking over — is enclosing a watercourse, road or square with a structure so that the space above it becomes usable. The earliest examples were brick barrel vaults over an urban stream, which is why the term is often used interchangeably with vaulting over.
Note the distinction from a culvert itself: a culvert is the individual pipe or box carrying water under a road, while culverting describes covering a length of open watercourse or route.
Applications
- Over water. Many urban streams and canals were culverted in the nineteenth and twentieth centuries to gain streets and squares. The watercourse still runs underneath. Current urban water management sometimes reopens these sections, because open water cools better, stores more and is easier to maintain.
- Over roads and railways. A building, park or square above a sunken road or rail line. It creates space and reduces noise and the severance effect in a city.
- Over cables and pipes. A concrete slab or channel above a services route taking the load of the paving build-up and heavy traffic and spreading it sideways, so the pipe itself stays unloaded. Such a load-relieving structure may also be temporary, for instance during a construction period with heavy cranes and deliveries.
Points to watch
- Inspectability. A culverted watercourse can no longer be seen. Without inspection chambers or access covers the condition of the brickwork or concrete cannot be assessed; collapses of old culverting almost always follow years of unnoticed decay.
- Flow and storage. The cross-section under the structure determines how much water can pass. An undersized culverting acts as a bottleneck in heavy rainfall.
- Silting and debris. What you cannot see, you do not clear. Culverted lengths silt up and collect debris at the inlet; a trash screen with a maintenance regime is essential.
- Load path and cover. Where culverting spans over pipes, the slab carries the load; it needs adequate bearing on undisturbed ground each side and must not rest on the pipe itself.
- Ownership and maintenance. The structure often sits at the boundary between the highway authority, the water authority and utility owners. Agree in advance who inspects and who maintains.
Related terms
- Culvert
- Encroachment
- Flood defence
- Pumping station
- Rainwater drainage
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