Culvert definition

A culvert is a closed conduit or tunnel used to convey water from one area to another, normally from one side of a road to the other side.

Typically culverts are box shaped, round or elliptical in cross section. They are often pre-fabricated and can be made from pipes, reinforced concrete or other materials that are embedded within the surrounding landscape to create a bridge-like structure that permits the stable and proper flow of water under an obstacle such as a road, and can help alleviate flooding and reduce erosion.

Culverts can also be used to move rainwater runoff along, under or away from highways.

The difference between a bridge and a culvert is that a bridge is intended to allow passage over an obstacle such as a body of water, whereas a culvert is intended to permit a body of water to pass under an obstacle such as a road. A culvert is provided for the ‘benefit’ of the water, and typically has a base over which the water flows. A bridge is provided for the passage of traffic, and provides a base over which that traffic can pass.

NB A drop inlet culvert is a form of culvert used on sloping ground where the water level has to be lowered to pass under a railway or road.

Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines a culvert as: 'A covered channel or pipe which prevents the obstruction of a watercourse or drainage path by an artificial construction.' It also gives the following definitions:

• Culvert condition appraisal as: ‘…the range of activities involved with the qualitative evaluation of an asset’s condition and performance (ie the gathering of existing data, inspection, investigation and structural assessment).’
• Condition assessment is: ‘ A measure or measures of the culvert carried our as a precursor to the performance assessment, for example, measurements of degrees of sedimentation or in situ tests on the fabric of the culvert.’
• Performance assessment is: ‘A comparison of present performance against performance requirements. The assessment considers the effect of a condition on each performance requirement and the effect of each performance requirement on the performance of the subsystem or system. The key to performance assessment is an understanding of the link between asset (or system) condition and its response under a range of loading conditions. Outputs of this stage are the probability of failure and residual life.
• Condition monitoring is: ‘Continuous or periodic inspection, assessment, measurement and interpretation of the resultant data to indicate the condition of the specific component. This will determine the need for some preventative or remedial action.’

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