Langstone Flood Maps

Why did we undertake flood modelling for this study?
Flood modelling was undertaken to determine the extent and depth of flooding for a range of flood levels over the next 100 years. Although flood modelling was previously undertaken for the Portchester to Emsworth Coastal Strategy (2012) it is now out of date and does not provide a suitable level of detail for the Langstone Study.

What do we use it for?
The outputs from the flood modelling are overlain with data from the National Receptor Dataset (NRD) which shows the location of buildings, heritage assets and utilities. In doing this we can identify and update the number of properties and assets at risk of coastal flooding under the different flooding scenarios. This information is then used to understand the level of economic damage that could occur under a ‘do nothing’ situation, which we then compare to the costs of ‘doing something’ to get a benefit cost ratio for the works.

This flood modelling has been produced at a strategic level to help shape the development of flood defence options for our study. Any use of the data or the maps for anything else is entirely at the risk of the person interpreting the information. The flood modelling has been developed using UK Climate Projections 2009 (UKCP09) data, not National Planning Policy Framework (NPPF) data which is required by the planning process for development proposals. The modelling takes account of the defences currently in place and assumes they remain in place at that level for the 100 years (this is different from the Environment Agency flood maps which assumes no defences in place).