Presence and Position of Sand Ridges on the Shelf Strongly Impact Decadal Evolution of Adjacent Shorelines: A Model Study

Several field and model studies indicate that the decadal evolution of shorelines is affected by the presence of shoreface-connected sand ridges (sfcr) and tidal sand ridges (tsr) on the shelf. This study uses a coupled shelf-nearshore numerical model to quantify the joint impact of tsr and sfcr on decadal shoreline evolution. Additionally, it examines the dependence of this evolution on cross-shore and longshore displacements of the sfcr, thereby mimicking the observed cross-shore and longshore migrations of sfcr on the shelf. Model results indicate shoreline progradation near the crests of the sfcr and retreat near the channels between the ridges and the coast, consistent with observations. Compared to sfcr, the impact of tsr on nearshore dynamics is smaller yet significant. When the sfcr are positioned closer to the shore, shoreline progradation and retreat become stronger. These shoreline undulations have amplitudes that strongly increase as sfcr approach the shoreline, and the undulations shift alongshore with the alongshore shift of the sfcr. Based on these results, it is anticipated that the observed onshore and alongshore migration of sfcr on the shelf will enhance shoreline retreat near the channels and progradation near sfcr crests, with these shoreline changes migrating alongshore with the ridges.