Flood Risk Assessment: Cherhill


This site was classified as Zone 3 on flood maps which effectively precluded any form of development.  Unfortunately Environment Agency mapping is undertaken at large scale and does not always fully reflect flood risk at any particular location, particularly small development sites.

E&M West were commissioned by Green Square to provide a flood risk assessment to support a change in classification to Zone 2, which would permit development subject to fulfillment of the relevant criteria.

Flood risk assessment here required consideration of fluvial (river), pluvial (overland flows), ground water and sewer flooding and began with a site walkover to prioritise investigations.  Relative levels are very significant and had to be contrasted with Environment Agency flood data for the River Brook behind the site.  Records were reviewed and residents interviewed to determine if their was any significant flood history.  The way existing provision operates is also key and attending site in heavy weather, as the photographs confirm,  had its advantages.

In this case the main risk was overland flow from the adjacent road, as the entrance was located at the bottom of a small hill.  Site levels were adjusted to provide an exceedance route, and a  SUDS scheme designed using permeable surfacing and gap graded aggregates to make use of limited infiltration at the top of the site, channeling  surplus water to a soakaway to the rear.


Client & Project Management: Green Square