Coupling TOMAWAC and EurOtop for Uncertainty Estimation in Wave Overtopping Predictions

An integrated model system has been implemented for downscaling from climate models, to wave climate and continental shelf models for tides and surge, to coastal models for waves and water levels and overtopping of sea defences and inundation. Within the system, the 3rd generation wave model TOMAWAC is applied to transfer inshore waves to the toe of the seawall, producing wave input for the predictive tool EurOtop that provides estimates of overtopping rates. This coupling is then used to assess the sensitivity of the overtopping predictions to uncertainty in offshore hydraulic conditions and beach levels for a case study on 7th November at Walcott in East Anglia, UK. The methodology used to transfer offshore conditions towards the nearshore allows estimation of the induced errors in nearshore wave heights by introducing small changes to offshore water level and significant wave height. Wave height uncertainty leads to an error in overtopping discharge rate less than 30 %. Errors induced by uncertainty in water levels are much higher. A + 10 % uncertainty in water level could increase the nominal overtopping discharge rate by a factor of 2.7. Thus, at least for this particular case, overtopping discharge predictions are mainly sensitive to water level. Uncertainty to beach profiles is also investigated showing that the overtopping is sensitive to low beach levels.