Recent bathymetric variability of sandbars at Duck, NC

Sediment transport and sandbar migration are unresolved research topics due to the complex interaction between waves, currents, and sediments in the nearshore region. Previous studies have led to better fundamental understanding of sediment transport, but the capability to make precise short term estimates is still limited. One challenge in predicting sediment transport is the sparse bathymetric data available to ground-truth predictions. A recently developed algorithm, cBathy, uses video images to estimate the nearshore bathymetry from wave celerity. This new method can provide an extensive time series of bathymetric change in order to further study the physics of short term sediment transport. The cBathy code is still under development and needs further testing for accuracy. The objective of this work is to validate cBathy estimates of bathymetry and quantify sandbar behavior over a two month period by analyzing the position of the sandbar crest.

The bias between the cBathy estimate and survey on 04/02/15 was 0.24 m and root mean square error (RMSE) was 0.50 m. The bias for the cBathy estimate and survey on 05/19/15 was -0.02 m and RMSE was 0.39 m. The bias and RMSE we observed were comparable previous estimates. As expected, errors were largest in shallower water depths where assumptions made by the cBathy algorithm were not valid.

Over the two month period, the mean cross-shore location of the primary sandbar at the alongshore location of 200 m was approximately 216 m, with a standard deviation of 16 m. The mean cross-shore location of the primary sandbar at the alongshore location of 850 m was approximately 205 m, with a standard deviation of 17 m.