Extreme values of coastal wave overtopping accounting for climate change and sea level rise

An integrated modelling system is presented for determining the wave overtopping of a sea wall due to offshore hydrodynamic conditions; the overtopping discharge depends mainly on the water level and the nearshore wave height. The modelling system enables joint probabilities for overtopping discharge to be assessed for different future climate scenarios with different rates of sea level rise. For the test case of a sea wall at Walcott, UK, where extensive flooding occurred on 9th November 2007, it is shown how the frequency of flooding of a given magnitude would increase with time, dependent on future climate projections and sea level rise, and, correspondingly, how the magnitude of flooding with a given return period would increase. For example, for an event with a return period of 100 years (similar to the 2007 Walcott event), the return period, estimated by the proposed extreme event analyses, reduces to 5 years with 0.35 m sea level rise in 2100, thought to be the most likely level, and just over 1 year with 1 m sea level rise. The methodology applied here, based on state-of-the-art modelling of wave overtopping, shows that the future projected rates are more influenced by changes in water level than by changes in significant wave height.

► An integrated modelling system is presented for determining the wave overtopping.
► Sea level rise and climate change impacts on extreme overtopping rates are analysed.
► Projected rates are more influenced by changes in water level than by changes in wave.