Mobility of meso-scale morphology on a microtidal ebb delta measured using remote sensing

Ebb tidal deltas usually consist of several large lobes of sediment separated by channels in which the bulk of the tidal exchange takes place. The purpose of this paper is to describe and quantify the migration pattern of bedform features associated with an ebb-tidal delta using a new remote video sensing method during a 23 day experiment at New River Inlet (North Carolina). To quantify the migration rates, a Lagged Least Squares Algorithm (LLSA) was developed that found the vector rate for which the suite of lagged images were most similar, computed on a tile-by-tile basis. Our observations revealed a complex set of bedform features that migrated in a circular pattern with movement in offshore regions being away from the inlet mouth and toward the shore while nearshore migration was back toward the inlet. 60% of the wavelength variability of these features is at scales that are smaller than the coherent channel and swash bar structures but much longer than megaripples, i.e., between 10 and 100 m. We have chosen to call these bedform features of meso-scale morphologies. The mean migration rate of these features was found to be 1.53 m/day ± 0.76 m/day. 72% of estimated rates were greater than 1.0 m/day, 31% were larger than 2.0 m/day, and the maximum rate was around 3.5 m/day, averaged over 23 days. Alongshore averages of cross-shore migration rates showed a node at 110 m from the shoreline that separates migration away from the inlet from migration toward the inlet (near the shore). The circular pattern of migration appeared to be consistent with expected residual flow of an ebb-tidal delta system.