SHORELINE RESPONSE TO STORMS AND THE CONFIGURATION OF NEARSHORE SAND BARS

Coincident observations of nearshore sand bar morphology and shoreline position are used to examine the coupling between the alongshore bar configuration and shoreline response to storms. The data were obtained along approximately 145 km of the Outer Banks of North Carolina on the central-eastern seaboard of the United States. Analysis focuses on a single storm event that occurred on 19-20 October 1997. Estimates of bar morphology are obtained from time-averaging aerial video of nearshore wave breaking patterns. Changes in the configuration of multiple sand bars are shown to be substantial, with as much as 80% of the inner sand bar of a two-bar system disappearing during the storm. Shoreline position, defined as the mean high water contour on the beach, was measured just before, during, and just following the storm using the GPS-based SWASH survey system. High correlation between the configuration of the bar system and the alongshore variability in shoreline change suggest that developing a predictive capability to forecast regions susceptible to erosion during storms may be possible, thus leading to improved rapid response strategies prior to the onset of large hurricanes or nor'easters common to the North Carolina coastline. Finally, observations show that changes in large scale, O(10 km), obliquely-oriented sand bars are consistent with an alongshore migration of about 1-2 kilometers over a period of 17 days following the storm. Such large alongshore migration rates have not previously been observed, and suggest that alongshore directed bar movements may have a significant impact on large scale sand bar variability.