Attenuation reservoir 'failure'
Emersons Green, Bristol
During severe autumn weather, several newly completed houses in the Emersons Green regional development at north Bristol were seriously flooded. The incident was widely reported in the local media, with adverse publicity.
Initial reaction was that one of the local attenuation reservoirs had overfilled and was the cause of the flooding. The client requested a full appraisal of the drainage system, a complex linked system of trunk sewer, attenuation reservoir and receiving watercourse.
An objective analysis of all relevant conditions, using both reservoir simulation and storm sewer models in fact proved that the flooding arose from the trunk sewer manholes further upstream. The reservoir operated as designed, although debris had blocked the outlet, leading to high tailwater levels. It was concluded that inadequate surcharge allowance in the sewer design, coupled with lack of maintenance of trash grills was the main cause of failure.
Recommendations were also made to improve the reservoir spillway design
Client - Bryant Homes
Date - November 2001
Funding - Client
Support tools - WALLRUS, StormCAD, FEH