Mechanisms and timescales of beach rotation

Abstract

In a simple definition, beach rotation is the opposing movement of the shoreline along the two ends of an embayed beach, driven by longshore and/or cross-shore sediment transport in response to seasonal or periodic changes in wave direction and/or gradients in wave energy. However, when considered in detail, the mechanisms, drivers and timescales of beach rotation are complex, resulting from non-linear interactions of cross-shore and alongshore hydrodynamic forcing, sediment transport and morphological change, developed over single or combined timescales that range from storm events to decadal rotation driven by climate-forced changes in wave conditions. In the context of global change, morphodynamic complexity of beach rotation processes is further compounded by rising sea levels and changes in wave climate, and impacted by artificial modification of beach environments along increasingly engineered coastlines. The spatial and temporal complexity of beach rotation mechanisms creates significant challenges to morphodynamic modelling and management of embayed beaches.