Side-Scan Sonar Studies of Surf Zone Bed Morphology
Dickson, P.J., and Drake, T.G., 1998, Side-scan sonar studies of surf zone bed morphology: EOS Trans. AGU, 79(17),Spring Meeting Suppl., S121.
Side-scan sonar images obtained daily during the SandyDuck97 Coastal Field Experiment at Duck, North Carolina reveal dramatic temporal and spatial variations in seafloor morphology in the surf zone. Twenty survey profiles spaced about 25 m apart in the alongshore direction covered a 500 m by 500 m region from dry land out to water depths of about 5 m. Images extending about 48 m on either side of each profile line were acquired with a digital side-scan sonar mounted 1 m above the seafloor on a unique motorized tripod called the Coastal Research Amphibious Buggy or CRAB. Differential GPS and ancillary measurements are used to locate the sonar. Particularly striking are transitions from a relatively smooth seafloor having plane bed or cm-high wave ripples to a rough, megarippled bed over timescales of no more than one day. Such transitions are strongly correlated with episodes of increasing wave height and decreasing wave period. Transitions from a megarippled bed to smooth seafloor occur at comparable rates, but do not correlate simply with wave conditions. Spatial variation in bottom morphology, even at the same cross-shore location within the survey region, is equally striking.
Supported by the Office of Naval Research and Army Research Office.