Effect of sea level rise on the overtopping of English coastal defences

Abstract

With a rise in sea levels, there is a consequent increase in the risk to coastal communities of the severity and magnitude of flood events. However these increased risks are not spatially consistent, and the type and nature of a coastal defence may influence the change in the risk at a location, and to what extent levels of mitigation may need to be implemented. This paper therefore investigates the impact of the change in risk of coastal flooding around England as a result of sea level rise. It involves the application of components of an existing risk-based coastal flood risk analysis method for a subset of almost 600 defences to rises in sea levels up to 1m. The resulting analysis shows that overtopping rates increase at a much greater rate for low return period events, which can be in excess of 100 times. The analysis also shows that the change in overtopping rate is a function of the defence type, with the relative changes for sloping defence structures significantly greater than for vertical defence structures