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Abstract: Episodic Atmospheric Forcings and Bayside Shoreline Erosion; Santa Rosa Island, Florida

Charles K. Armbruster, Gregory W. Stone, J. P. Xu

Preliminary findings indicate that atmospheric forcings associated with intense winter storms play a significant role in the evolution of bayside shorelines along the Northeast Gulf of Mexico. Retrogradation of the north-facing bayside shoreline may exceed 0.5 m due to a single frontal passage, where the fetch is non-limiting. Although masked within the long-term effects of a rise in relative sea-level in the Gulf, chronic erosion is evident at sites where fetch is large by outcropping of peat deposits in the foreshore, exposure of in situ tree roots, and erosion of dune/beach-ridge deposits. Atmospheric forcings associated with periodic cold front passages significantly augment wind and wave activity in the bayside nearshore environment. Consequently, sediment i transported to the interior of the island via eolian processes as well as by wave action within a complex network of reticulated transverse bars.

During the winter of 1995, a series of beach and nearshore profiles was surveyed along the north shore of Santa Rosa Island, Florida to quantity net sediment movement during several frontal passages. For one of these events an array of instruments was deployed including a two-dimensional current meter, ultrasound sensor, anemometer and wind vane to monitor wind and hydrodynamic conditions.

A general model is presented which demonstrates fluctuations in the beach-nearshore profile during cold front passages. Data suggest the bayside shoreline is transgressing gulfward as the nearshore-beach profile continuously responds to changing wave energy and varying water levels during storm and fair-weather conditions.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana