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Photograph - Culvert inlet

Expert witness,
flooding from a culvert

Small culverted watercourse in southern England

One of our senior staff acted as an expert witness in a case involving flooding from a small culverted watercourse in southern England. A blockage had formed in the culvert which resulted in extensive flooding to two properties during a period of high flows caused by heavy rainfall combined with melting snow.

Engineering Calculations

To enable an opinion to be formed various engineering calculations were undertaken. These included estimating the peak flow from the culvert during the flood based on water levels observed by witnesses. The return period of the flood was then estimated by relating the calculated peak flow to a flood frequency curve derived by Flood Estimation Handbook methods. This showed that the flood was far more severe than would be suggested by the Met Office rainfall data alone. This information, together with estimated peak flows in the watercourse in the weeks prior to the flooding (due to both rainfall and also a burst water main) allowed the flood itself to be put into its proper context.


Our expert witness provided opinion on the obligations of the various parties, the speed of occurrence of the flooding and the reasonable steps which one of the parties could have taken prior to the flooding. The significance of several warning signs which occurred before the flood itself was also considered.

Further information

For further information regarding our expert witness services, please see our Expert Witness page or please contact us.

Photograph: Inlet to the culvert. The screen (grill) was removable.