Quantifying Seasonal Shoreline Variability at Rehoboth Beach, Delaware, Using Automated Imaging Techniques

Abstract We describe a seven-camera video system deployed at Rehoboth Beach on the Atlantic coast of Delaware that was used to monitor and quantify the evolution of a nourished beach. Shorelines along 6 km of beach were automatically identified using pixel-intensity gradients from time-exposure and variance imagery. Correlations between automatically identified and user-defined shorelines from images with various wave and atmospheric conditions exceed r2 values of 0.92. Small variations in camera azimuth and tilt were found to significantly affect apparent shoreline locations and were automatically corrected through image-correlation procedures. Hourly shoreline data were tidally and seasonally averaged to quantify seasonal morphodynamic variability. Over a summer-winter-summer monitoring period, the shoreline exhibited erosional and accretional variations of ∼10 m dependent in the alongshore direction on permanent man-made structures and subject to seasonally characteristic littoral transport variations. A comparison of mean seasonal shoreline locations revealed a mean erosion value of ∼0.8 m between the summer of 2006 and the summer of 2007; this erosion rate is consistent with previous studies of this area. The temporal history of the planform area, obtained from shoreline position, showed weak correlation with volumetric measurements and thus could not be used as a proxy for volumetric change at this site.

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