Vulnerability of coastal defences to climate change

Climate change will alter wave and water level conditions and hence affect the vulnerability of coastal defence structures. The likely changes in vulnerability are important to the stakeholders in new and existing coastal defence structures, as decision-makers may reasonably be expected to include the probable effects of climate change in their planning processes. Time series of present and future waves and water levels were generated using a climate model. These were used to calculate the changes in overtopping rates and in the longshore drift of sediment in front of sea defences. The results indicate that there will be considerable increases in overtopping rates if present-day defences and beaches are unchanged by 2075. However, the inclusion of sea level rise predictions in design calculations should account for the majority of the predicted change in overtopping. The work also indicates that future changes in longshore transport are unlikely to be greater than current levels of uncertainty, and these should be considered in the normal course of sensitivity testing. Qualitative and quantitative differences in future changes in vulnerability were found between the five sites examined, as they had different tidal ranges, wave climates, surge levels and joint probabilities.