Abstract
Barrier island overwash occurs when the elevation of wave runup exceeds the dune crest and induces landward transport of sediment across a barrier island and deposition of a washover deposit. Washover deposition is generally attributed to major storms, is important for the maintenance of barrier island resilience to sea-level rise and is used to extend hurricane records beyond historical accounts by reconstructing the frequency and extent of washover deposits preserved in the sedimentary record. Here, we present a high-fidelity 3-year record of washover evolution and overwash at a transgressive barrier island site. During the first year after establishment, washover volume and area increased 1595% and 197%, respectively, from at least monthly overwash. Most of the washover accretion resulted from the site morphology having a low resistance to overwash, as opposed to being directly impacted by major storms. Washover deposits can accrete landward over multi-year time scales in the absence of large storms; therefore, paleotempestites can be more complex than single event beds.
Highlights
Barrier island overwash occurs when the elevation of wave runup exceeds the dune crest and induces landward transport of sediment across a barrier island and deposition of a washover deposit
To better understand the transition of a barrier island from a coastal morphology that was resistant to overwash to one experiencing overwash and washover deposition, we present a 3-year time series of oceanographic conditions, overwash, and morphologic changes
Most of the deposition of washover sediment occurred in the absence of large storms, mainly due to the low resistance of the site to overwash
Summary
Barrier island overwash occurs when the elevation of wave runup exceeds the dune crest and induces landward transport of sediment across a barrier island and deposition of a washover deposit. Transport of sediment and water across a barrier island during increased ocean-water levels and wave heights, termed overwash, can be highly detrimental to infrastructure[1], human health[2], and economies[3] Despite those hazards, overwash is essential for sustaining barrier islands faced with rising sea level because it fortifies the island by moving sand landward and depositing it as elevated washover terraces and fans. This storm-induced deposition expands island width and height Island expansion increases both immediately during overwash events by shifting back-barrier areas into intertidal and supratidal elevations, and gradually through subsequent years by reducing the density of sand-trapping fore-dune vegetation, which promotes aeolian transport of sand landward across the island and the formation of incipient dune fields as grasses reestablish. Washover accretion could occur over timescales longer than an individual storm event caused by island morphology being conducive to frequent overwash
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