GROUND PENETRATING RADAR ANALYSIS OF SAND BAR DEPOSITS IN THE BONNET CARRE SPILLWAY FROM THE 2019 FLOOD

The Mississippi delta is losing land at rates that threaten coastal communities. Recently, engineered sediment diversions have been discussed and begun to be implemented as a way to reconnect the Mississippi River to its floodplain and coastal marshes to help rebuild and maintain land. The 2019 Mississippi River flood was one of the largest ever recorded. As a result, the Bonnet Carre Spillway, an engineered flood control structure upriver of New Orleans, was open for a record 123 days. This flood also marked the first time this engineered diversion was opened in consecutive years and twice within a single year. Such spillway openings provide an opportunity to characterize the potential sedimentation patterns and dynamics within engineered diversions. During the 2019 flood large quantities of sand were deposited in the Spillway. In order to characterize these sand bars, we deployed a 250 mhz ground penetrating radar to image the subsurface. The data collected was then processed using an open-source program named RGPR. The processing steps included: setting the zero time, a dewow filter, a high frequency filter, and a power gain in order to compensate for signal attenuation. After processing we were able to characterize bar scale features, clinoforms with heights of 1-2 meters were interpreted in the panels. In conjunction with additional work being conducted on these spillway deposits, we hope this data will form a part of a complete characterization of the depositional processes within an engineered flood-control diversion and may be used to help inform future models for engineered sediment diversions.