Introduction: Predicting flooding and calculating flood risk is complex. The Environment Agency provides information on the risk from river flooding (fluvial) and sea breach, but information on floods caused by direct runoff (pluvial) is limited. The extreme precipitation of July 2007 caused at least one pluvial event in the WPD region and there is a need to identify the potential risks at critical sites.

Objectives: Pluvial flooding results from high intensity or prolonged heavy rainfall leading to overland flows and ponding. Flooding can also occur due to exceedence or blockage of watercourses and drainage systems. The risk depends upon a number of factors including topography, amount of impermeable surface within upstream catchment areas and the drainage capacity within the catchment area.

Using a series of modelling tools on GIS and OS data will allow catchment areas around critical sites to be identified and the quantity of runoff calculated. Existing drainage and watercourse features can then be modelled and restrictions identified where pluvial risks are identified. Information from the DEFRA ‘Making Space for Water’ programme will be included.