Probabilistic coastal flood forecasting

The project described in this paper includes development of surge ensemble modelling for the UK, and demonstration of probabilistic coastal flood forecasting for an area in the Irish Sea. Its purpose is to develop, demonstrate and evaluate probabilistic methods for surge, nearshore wave, and coastal flood forecasting in England and Wales, but the concepts and models would be equally applicable elsewhere. The main features that distinguish these methods from existing practice are in the use of hydraulic models extending through to action at coastal defences, and the use of ensemble and other probabilistic approaches throughout. Use of offshore forecasts to estimate the likelihood of high overtopping as an indicator of coastal flooding is not trivial, involving transformation of wave forecasts through the nearshore and surf zones, and the combined effects of wind, waves and sea level in causing overtopping; with sufficient accuracy and reliability for acceptance, and sufficient lead-time for actions to be taken to reduce potential losses. The Environment Agency has responsibility for fluvial and coastal flood forecasting for England and Wales. The Met Office has operational responsibility for offshore forecasting for the UK.