Buckinghamshire Council Culvert Policy

Compared with an open channel there is an increased risk of blockage once a culvert is installed. If the blockage occurs within the culvert, there is much greater difficulty in removing it. Maintenance on culverts is more costly and time consuming than for open channels.

It is sometimes argued that culverting will reduce the problem of open channels being subject to litter and fly-tipping. Such short-term advantages are outweighed by the overall disadvantages, and alternative means should be pursued to address waste issues.

Flooding is more likely to result from culverts when they become obstructed, and culverted channels also provide less flood storage than open ones. There have also been cases of serious flooding caused by culverts collapsing due to root damage from vegetation or the weight of development above them.

Culverting will create less permeable bed to a watercourse and often increases the speed of water flow, possibly increasing flood risk downstream and also preventing local recharge of groundwater. Culverted sections may also create or exacerbate downstream or upstream bank and bed erosion or promote sediment deposition, as a result of altered water velocities and disruption to the natural transport of sediment.

Culverting has a detrimental impact on the environment, resulting in a complete loss of features within a watercourse. The continuity of the river corridor is broken, adversely affecting the landscape and ecological value of the watercourse for migrating species. An existing or potential amenity is also lost for present and future generations.

Drain connections are more easily made to open watercourses where the performance of drainage systems can be visually monitored. Outfalls within culverts are prone to blockages or, in the case of flapped outfalls, can seize up. Maintenance of these outfalls is considerably easier in open channels where access is better.

Culverts conceal the presence of a watercourse and can lead to development or unacceptable land-use above or near them. In many urban areas buildings have been constructed above or adjacent to culverts. This means that improving standards of flood protection or accommodating run-off from future developments could be impossible or uneconomic due to the cost of replacing or enlarging existing culverts. The visible presence of a watercourse, reminds developers and the public that there is a risk, whereas this can be concealed and overlooked if the watercourse is culverted.

The responsibility for the condition and maintenance of a culvert lies with the landowner or the owner of the culvert unless other agreements are in place. The responsible party must therefore ensure that the culvert remains in good condition and free from obstructions. Failure to do so could result in liability for any damage caused by flooding. Access to culverts is generally safe only with the use of special procedures and equipment, making inspection and maintenance both difficult and costly.

There are dangers associated with natural open watercourses but culverted watercourses can be equally as dangerous. Culverting does not remove the risk of drowning or injury. There have been many cases in the past where children, and adults have died or suffered injury after entering culverts and they therefore represent a considerable safety hazard. Working within culverts is seen as confined space working which requires special training. Water levels can rise suddenly and without notice, and there can be a lack of oxygen or build-up of potentially toxic or explosive gases in culverts. All these hazards are a danger both to the public and to operatives when maintenance is required. Working within or near to a watercourse also requires special safety training for operatives.

Culverting a watercourse makes the early detection and tracing of pollution sources more difficult, resulting in the adverse impacts being more serious.

There is further impact on water quality due to the loss of the biological processes which are essential for river purification, and there is normally a reduction in oxygenation of water passing through a culvert. Culverting may also result in stagnant water problems, particularly if culvert levels are badly planned or constructed.