Synchronization of transport and supply in beach-dune interaction

TLDR

The lack of information on how and when sediment is transferred to the backshore limits the development of a scalable theory of beach‑dune interaction, as existing models treat the beachface as a static transport surface and ignore the processes that supply sediment for dune growth. This review examines how nearshore processes and morphological change act as flexible constraints on sediment supply and transport between beach and dune. Dune recovery after storm erosion requires beach recovery through onshore migration and welding of nearshore bars, followed by backshore accretion that creates a sediment supply for wind transport. Process‑scale studies show that sediment transfer across the beachface is spatially variable and temporally intermittent, and that dune recovery depends on synchronizing transport events with backshore sediment supply, creating an asymmetry that makes barrier islands vulnerable to erosion and breaching when storm patterns shift.

Abstract

This review considers the role of nearshore processes and morphological change as a flexible and dynamic constraint on the supply and transport of sediment between beach and dune. It is argued that the lack of information in this regard remains a central barrier to the development of a theory of beach-dune interaction that can be translated across scales and between field sites. Existing beach-dune models do not consider how and when sediment gets transferred to the backshore where it becomes available for transport by wind. Rather, existing models largely ascribe regional variations in dune morphology to fixed constraints on beach slope and sediment budget, without explicit recognition of processes involved. Recent (process-scale) transport studies have shown that the transfer of sediment is both spatially variable and temporally intermittent as a result of transport limitations across the beachface. While these studies have identified varied controls on sediment transport and exchange, there remains a limited capacity to predict the evolution of beach-dune systems, largely because the beachface tends to be viewed as a static transport surface without regard to supply or to the changing limits to transport. Following storm erosion, dune recovery first requires that the beach recovers through the onshore migration and welding of nearshore bars, followed by accretion in the backshore to create a supply of sediment for transport by the wind. The dependence of dune recovery on the synchronization of transport events with the recovery of sediment supply in the backshore creates a strong asymmetry in dune recovery that makes barrier island susceptible to widespread erosion and breaching if a change in the frequency or grouping of storm events is capable of resetting the bar system (offshore) before the next extreme storm.