The depth-varying response of coastal circulation and water levels to 2D radiation stress when applied in a coupled wave–tide–surge modelling system during an extreme storm

• Application of 2D radiation stress within a coupled 3D circulation-wave model.
• Assessment of the importance of radiation stress during an extreme storm.
• Development of methods for accurate operational forecasting.
• Impact of radiation stress across shallow water and estuarine regions.

During storm events wave setup in shallow regions can contribute significantly to the total water elevation, and radiation stress can also generate alongshore drift influencing sediment transport. In low lying coastal regions this generates the potential for flood inundation and morphological change. A coupled tide–surge–wave modelling system is therefore required for accurate forecasting. Liverpool Bay, UK, is taken as a case study because it has a resource of observations and incorporates three estuaries, thus providing conditions to assess the model performance both at the open coast and within estuarine environments. The model covers a region encompassing depths from about 50 m below the mean tidal level to shallow wetting and drying regions, and has previously given good wave and surge hindcasts both for individual storm events and multi-year studies.The present study builds on an already accepted model, to include and assess the spatial influence of 2D radiation stress when implemented in a 3D circulation model. The results show that the method is computationally efficient, so relevant for operational use, and also provides a plausible solution. The varied influence of radiation stress across a coastal domain is demonstrated, with larger impact at an estuary mouth and along the open coast, while having lesser impact within an estuary and further offshore.