X-Band Radar Mapping of Morphological Changes at a Dynamic Coastal Inlet

Abstract

Remote sensing of the complex interactions between bathymetry, tidal flow, and waves in coastal inlets provides high-resolution data sets that can be exploited to characterize the morphological variability of shallow ebb tidal deltas (ETD). Here we used observations from a mobile X-band radar platform to determine optimal conditions during which radar-derived shoal signatures best represent positions of underlying shoals. Significant increases in the spatial errors of radar shoal signatures were observed when offshore wave energy intensified. Consequently, the lowest spatial errors occurred when the radar shoal signatures were primarily a function of the tidal flow (i.e., low sea state). We used these findings to quantify shoal migration patterns at the New River Inlet, North Carolina. We found that the southwestern portion of the ETD had the largest morphological variability with typical shoreward migration rates of 2–3 m/day driven by incident wave energy. The migration rates and patterns estimated from X-band observations were consistent with numerical modeling results and a previous video-based New River remote sensing study. Our results confirm that X-band radar can be used to quickly map shallow ETDs (e.g., 5 min of observations), allowing for rapid morphological assessments from shore or boat-based platforms. The methods would prove particularly useful for initial assessment as well as continual monitoring of dynamic tidal inlets where large morphological responses can be rapidly assessed and used for geomorphological studies, and as decision aids for maritime or engineering operations.