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Coastal Flood Risk Assessment – Grimsby

GeoSmart was instructed to undertake a FloodSmart Plus report on behalf of a client to assess the nature and potential significance of coastal flood risk to land upon which a group of residential houses was being proposed in Grimsby.

The increase in surface water runoff from the site, due to the impact of the proposed development, was also considered and the flood risk assessment followed the standard outlined in the National Planning Policy Framework (NPPF, 2012).

A review of the data reported that the site had been identified as lying within the Environment Agency’s Flood Zone 2 with a greater than 1 in 1000 year annual probability of coastal flooding.

Usually new residential developments within Flood Zone 2 should be very carefully considered. In this case, however, since a significant proportion of the Local Authority district lies within a designated Flood Zone 2, there are limited options for development. As such the boundaries under which redevelopment plans are considered are less stringent than typically found.

To assess the coastal flood risk to a site within a Flood Zone 2 the Environment Agency (EA) is contacted to obtain modelled flood defence breach locations and associated flood depth and flow velocities for both present and future climate scenarios. Using this data, minimum floor levels can be recommended and an assessment of available flood evacuation routes during a flood event can be made.

For this site, modelled EA flood data suggested that the majority of safe egress routes would be affected during a flood. However, using the maximum flow velocity provided by the EA, an estimated time for the flood water to reach the site was calculated which illustrated that there would be sufficient time for occupants to evacuate. It was recommended that a flood evacuation plan was put in place and that site occupants signed up to the EA’s flood evacuation warning service.

This proposed plan was accepted by the Local Authority and the Environment Agency.

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