| In this study we describe a video system deployed at Rehoboth Beach on the Atlantic coast of Delaware to monitor and quantify the evolution of a nourished beach. Hourly time exposure and variance images from seven (7) cameras are geo-rectified to a horizontal plane at the tidal elevation in a local coordinate system. Shorelines along 6 km of beach are automatically identified using pixel intensity gradients from the time exposure and variance imagery. Correlations between automatically identified and user-defined shorelines from images with various wave and atmospheric conditions exceed r 2 values of 0.92. Small variations in camera azimuth and tilt are found to significantly affect apparent shoreline locations and are automatically corrected through image correlation procedures. Hourly shoreline data are tidally and seasonally-averaged to quantify seasonal morphodynamic variability. Over a year and a half monitoring period the shoreline exhibits erosional and accretional variations of ∼10 m that are highly dependent in the alongshore on permanent man-made structures and subject to seasonally characteristic littoral transport variations. Comparison of mean summer shoreline locations reveals an average erosion of ∼0.3 m between the summer of 2006 and the summer of 2007, consistent with previous studies of this area. The temporal history of the planform area, obtained from shoreline position, showed weak correlation with volume measurements and thus cannot be used as a proxy for volumetric nourishment performance at this site. |
