Coastal profile response to sea level rise: a process-based approach

Prevailing ideas and calculations of coastal response to sea level rise (SLR) are often based on the Bruun model (Bruun P., Sea-level rise as a cause of shore erosion, Journal Waterways Harbors Division, ASCE 88: 117130, 1962) that predicts upward and landward transfer of an equilibrium profile during SLR through offshore sediment transport on the shoreface. The model is based on a number of assumptions of questionable validity as well as outdated concepts on how sediment is transported across the shoreface. This contribution takes a numerical modelling approach that is based on first-order processes contributing to the movement of sediment across the shoreface. Using a wave transformation model that predicts hydrodynamic processes driving cross-shore sediment transport and an energetics-based model for the coupling between hydrodynamics and sediment transport, we show that cross-shore sediment transport is mainly onshore directed at the boundary between the lower and the upper shoreface, in agreement with the model proposed by Davidson-Arnott (Conceptual model of the effects of sea level rise on sandy coasts, Journal of Coastal Research 21: 11661172, 2005). The transition from onshore to offshore directed transport is located well within the surf zone and with a rising sea level this transition point becomes displaced landward and upward. Tests also show that substrate slope is of fundamental importance to the manner in which beaches react to rising sea level. Copyright (c) 2012 John Wiley & Sons, Ltd.