Shoreface sediment availability offshore of a rapidly migrating, mixed-energy barrier island

Abstract

Less is known about sediment exchanges between shorefaces and mixed-energy barrier islands (MEBI) than between shorefaces and wave-dominated barrier islands. We used seismic stratigraphy from Cedar Island, Virginia, USA to understand the interplay between shoreface deposits and MEBI morphodynamics. Interpretations reveal that the shelf and shoreface are extensively dissected by breach and inlet channels. Shoreface morphology varies due to underlying lithology and variable rates of barrier retreat. Underlying lithology adjacent to breach channels affected their migration rates, thereby exerting controls on alongshore extent of shoreface erosion. Shoreface deposits reworked by a migrating breach have lower slopes than those reworked by a more stationary one. Elevated rates of barrier retreat in southern Cedar Island may cause flattening of the shoreface because rapid barrier island migration required increased onshore sediment fluxes. In summary, barrier breach pervasiveness at MEBI may play an outsized role on shoreface ravinement and morphology. Ultimately, analyses of shoreface architecture and morphology provide insight on the relative influences of inlets, geology, and sea-level rise on barrier island sediment fluxes, which could help inform coastal planners, improve parameterization of shoreface sediment flux, and further future studies of morphologic change at MEBI.