Reshaping the understanding of beach response to sea-level rise for equilibrium shoreline modelling

With climate change and accelerating sea-level rise (SLR), long-term predictions of shoreline evolution are crucial to assess climate adaptation plans in coastal areas. Meanwhile, knowledge gaps in the physics of shoreline response to the combined action of waves and SLR hinder making reliable long-term shoreline projections. Equilibrium beach theory states that a beach profile shape equilibrates with its local wave and sea-level conditions. In the context of equilibrium beach theory, we present a physical interpretation of beach response to SLR that leads to the identification of two main contributing processes: passive flooding and increased wave-driven erosion efficiency (i.e. wave reshaping effect). Using this new interpretation, we analyze data from existing laboratory studies that measured the equilibrium beach response to controlled SLR and wave conditions. The data indicate a clear relationship among the analyzed variables, corroborating the potential of the proposed concept, and improving the understanding of shoreline response to SLR. Our results support the integration of SLR-driven recession into equilibrium shoreline models for future studies, making a step towards the development of a generalized equilibrium shoreline model.