Geomorphic response of inlet barrier islands to storms
Inlet Barrier Islands (IBIs) are infrequently studied, and are often poorly represented in coastal lidar records. The fetch limited barrier island (FLBI) model was introduced to describe geomorphic changes of IBIs over time. The FLBI model predicts that the morphology of IBIs should remain largely static during predominate weather conditions due to sheltering from oceanic wave energy but undergo significant erosion when local and non-local waves magnify during storms, subsequently failing to recover volume and elevation losses. Using three years of high-frequency small unoccupied aircraft systems (sUAS, aka drone) surveys and existing lidar records, we document geomorphic changes on Bird Shoal (a protective IBI near the town of Beaufort, NC) resulting from storms and predominate conditions, testing the FLBI model and documenting island evolution. Our results indicate that Bird Shoal exhibits different spatial trends in erosion, accretion, and shoreline migration across its 4 km length, likely driven by varying shoreline orientation to the Beaufort Inlet and back barrier bathymetry in Back Sound. Our data indicate that the geomorphic behavior of Bird Shoal currently does not adhere to the classic FLBI model. Foreshore storm recovery and growth on Western Bird Shoal and shoreline retreat on Central Bird Shoal occurred during predominate conditions, and beach morphology was not an artifact of past storm events. The Western Bird Shoal shoreline consistently retreated landward in decades of historic imagery, but transitioned to seaward expansion sometime between 2011 and 2014. This shift is likely driven by erosion of the western end of Shackleford Banks and concurrent widening of the Beaufort Inlet, allowing increased wave energy to enter the back-barrier sound and push flood deltas onto Bird Shoal during predominate conditions. Our results suggest that open ocean inlet width and location interact with back-barrier deltas to control sediment supply and wave energy for IBIs, and that IBIs may fall into and out of conformance with the FLBI archetype over time. This study demonstrates sUAS deploying frequently over a municipal scale to fill spatial and temporal gaps in traditional coastal remote sensing datasets.
Seymour, AC; Ridge, JT; Newton, E; Rodriguez, AB; Johnston, DW
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