The Challenge

Bilbrook is a growing village not far from the outskirts of Wolverhampton and near to the i54 industrial park by Junction 2 on the M54. A field on the village’s northern edge is being considered for residential development but is bounded by the Moat Brook on one side and by a sewage works on another.

The Environment Agency indicative mapping showed a substantial portion of the site falling within Flood Zone 3 and this significantly curtailed the potential area available for development. The predicted flood patterns also did not appear to fully match the topography, following a detailed land survey. SYSTRA was engaged to assess the flood risk in detail and to identify a strategy to enable development to proceed on a more substantive basis.

SYSTRA's Role

SYSTRA’s scope of study included reviewing an earlier river model provided by the EA, the impact of more recent climate-change predictions upon future flood behaviour and the consistency of the earlier model with the detailed site survey now available for the land in question. A preliminary flood management strategy was devised that used compensatory excavation to create new flood storage on site close to the WwTW, where development would be prevented by the proximity of the works.

A second phase of investigation involved compilation of a new river model encompassing the Brook reach past the site and downstream to its confluence with a larger river and, en route, a large culvert that conveyed a canal above the stream. We compiled a HecRas model of the stream, validated this against the earlier model and tested it with revised hydrological estimates to identify the Flood Zones under the new model. This was then used to successfully challenge and modify the EA’s indicative mapping. In turn, this informed a revised development model that would enable some residential usage of the site to be promoted under the local authority’s emerging development allocations.