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Dewees Island Beach Erosion Study

The beach of Dewees Island, like that of all barrier islands, exists in a constant state of flux.  The interaction of physical processes such as waves and tides with available sediment supply dictated by local coastal morphology and underlying geologic framework help establish patterns of erosion and accretion.  These patterns of erosion and accretion are not mutually exclusive; both may exist simultaneously at different locations along the same stretch of beach.  They also change over time.  Monitoring the condition of the beach at discrete time intervals provides insight into the relative stability of the beach and can be used to help create best management practices.

Dewees Island has been part of a regional shoreline monitoring project undertaken under the auspices of a partnership between Dewees Island and the College of Charleston, specifically Dr. Leslie Sautter.  Begun in February 2006, the partnership has supported data collection and analyses every year since, including the graduate degree of Betenbaugh, 2007; Dumars, 2007; and Sutherland, 2010.  The Dewees Island Conservancy is currently funding this  ongoing project.

Over the course of the monitoring period, the beachfront at Dewees Island has experienced tremendous change, most of which can be attributed to the process of shoal bypassing.  During these events, discrete packets of sediment break away from the larger ebb-tidal delta complex and migrate onshore, eventually re-nourishing the beach.  However, during this migration phase changes in wave refraction patterns revert to pre-attachment conditions.  This process leads to the subsequent stabilization of previously eroded areas via the redistribution of shoal sediment.

As you walk the Dewees beach today, you can readily see the new dunes forming, grasses taking root and spouting and the stumps along the mid-beach areas slowly being covered with sand.  Our evolving beach is fascinating to monitor from both the scientific point of view and the casual observer’s deep appreciation.

March 2009: Sand shoal off shore causes narrow channel to severely erode the central beach, in particular near Osprey Boardwalk. The ocean nearly breaches the dunes near Lake Timicau.

May 2010: Sand shoal attaches to beach and accretion phase begins.

October 2010: Sand continues to come on shore.

 

October 2012: Large amounts of sand continue to come on shore in accretion phase.

Article by Gary McGraw

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