222-6 Changes in the position of sorted bedforms offshore Folly Beach, SC (USA), over the last 30 years

Session: Delta Evolution from Rivers to the Shelf: Past, Present and Future Perspectives for Society (Posters)

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Abstract:

Modern barrier island systems create a complex interplay between the processes of waves, winds, tides, and biota interacting with a complex geologic framework in the near-surface and surface of the inner shelf and back-barrier regions.  While models oversimplify these complex interactions and resultant interpretations of change, understanding the distribution of materials on the shelf can provide more realistic inputs and thus outputs for the engineering community.  One such feature that complicates hydrodynamic modeling of the ocean-seafloor interaction is variably distributed bedforms of widely different grain sizes and ripple sizes.  Linear rippled scour depressions are one of these types of features, and they are a subtype of self-organized bedforms generally found in high-energy coastal environments.  Often narrow (meters to hundreds of meters), these bedforms extend from the lower beachface into the offshore zone beyond a theoretically-derived closure depth. In addition, these self-organized features of coarse material are often contained within their own shallow depression relative to its surroundings.  This study examines change in sorted bedforms off the coast of Folly Beach, South Carolina, over the last thirty years with a series of sidescan sonar surveys, high-resolution subbottom profiles, and physical samples from the seafloor. This study: 1) Identifies changes in the distribution of coarse and fine materials offshore Folly Beach over thirty years, 2) Calculates the changes in position over time, and 3) Provides a systematic approach to understanding change in this environment, as well as questioning previously proposed mechanisms of deposition. Building upon previous predictive models, the outcomes here are used to more accurately hypothesize what coastal processes have caused such shifts and how the features have maintained coherence over time. This study also proposes a more formal classification system of these features as it pertains to coastal geomorphology and evolution on Folly Beach, and aid in the study of other coastal areas that have similar morphology.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10287

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