Assessing the effects of shoreface profile concavity on long-term shoreline changes: an exploratory study

摘要

Coastal erosion under the context of global sea-level rise has threatened societies living along the coast. The processes related to decadal- to centennial-scale shoreline changes are much more complex than those suggested by the Bruun effect. This paper derives a one-dimensional model to explore the relationships between shoreline change, profile concavity, and sediment fluxes in wave-dominated coastal systems where alongshore sediment transport dominates the shoreline changes. The model incorporates an exponential approximation of shoreface profiles into the shoreline Exner equation. We found an equilibrium relationship in which a stable morphology profile is maintained during synchronous changes in sediment loss (gain) and shoreline retreat (advance) distances. Complex shoreline retreat behaviours can be classified into two dynamic equilibrium cases that are either above or below this equilibrium relationship. For a given negative net sediment flux, the shoreline retreat slows when the shoreface morphology steepens (i.e. increased profile concavity), and vice versa. Likewise, for a given positive net sediment flux, the shoreline advance slows when the shoreface morphology becomes gentle (i.e. decreased profile concavity), and vice versa. Interestingly, the higher the net sediment flux is, the greater the influence of shoreline changes on shoreface morphology. The short- and long-term processes governing the shoreface morphological changes are also discussed. This study demonstrates the importance of shoreface morphological concavity on the shoreline changes. Furthermore, the presented first-order model might have the potential to be used as a quick assessment for future decadal- to centennial-scale shoreline changes in coastal management and engineering activities.