SURF'S UP: BUT DOES IT BRING SAND FROM OFFSHORE TO THE VIRGINIA BARRIER ISLANDS?

The Virginia barrier islands are one of the most dynamic and pristine island chains along the U.S. eastern seaboard. Consequently, these islands provide an excellent natural "laboratory" for analyzing and predicting island behavior. This research sought to determine the sources and "sinks" of sediments that nourish and erode the beaches, respectively. To that end, I collected 76 surficial sediment samples from Assateague Island to the north and 144 bottom sediment samples from the active shoreface (depth ≤ 10 m); sieved these samples using standard laboratory procedures; determined weight percent by grain size fraction; and compared the means and standard deviations of the offshore and Assateague Island samples to onshore (island) grain sizes. This method enabled me to examine the potential for longshore versus cross-shore transport (LST vs. CST). Results indicate that similar yet finer grain sizes exist between the islands and offshore samples throughout the island chain and suggest that the offshore regions cannot supply sediment to the islands via CST. Instead, storms cause the thin sand veneer that comprises the islands to "rollover" backbarrier marsh deposits. To the north, the match between Assateague Island sediments and the northern islands, along with geomorphological evidence, suggest that Assateague Island contributes sediment to the northern Virginia barrier islands via southerly LST. However, Wachapreague Inlet serves as a "sink" that traps LST sediment. Consequently, the islands are migrating landward due to a negative sediment budget, decreasing tidal prism, storms, and sea-level rise.