Early Geomorphic Adjustment Following Living Shoreline Installation Using UncertaintyAware sUAS Remote Sensing

Abstract

Salt marshes and adjacent sediment flats are connected coastal environments whose spatial configuration regulates sediment transport, habitat quality, and shoreline stability. These low-relief environments are exposed to a range of physical processes that drive degradation, reducing productivity and limiting ecosystem services. Historically, shoreline stabilization has relied on hardening approaches, but recently nature-based solutions like engineered living shorelines have been increasingly used to promote shoreline stability and maintain ecological function. Evaluating geomorphic responses to these installations requires monitoring frameworks capable of resolving fine-scale, variable change across the marsh-intertidal-nearshore gradient. At the Theodore Roosevelt Natural Area located on Bogue Banks barrier island, a Natrx ExoForms™ oyster breakwater was installed in late 2024. This study uses established small uncrewed aerial systems (sUAS)-based field and structure-from-motion Multiview stereo (SfM-MVS) methods to generate repeat pre- and post-installation topographic products capable of quantifying early shoreline and intertidal surface change. Multiscale model-to-model cloud comparison precision maps (M3C2-PM) were used to detect fine-scale geomorphic change at the 95% confidence interval, and DEMs of Difference filtered using the 95% linear error (DoD-LE95%) were used as a raster-based comparison method. Results showed early-stage geomorphic adjustment across the study period, with the largest net lowering and sediment redistribution occurring between the baseline and first post-installation surveys. Across all survey periods, M3C2-PM detected a greater area of statistically significant change than DoD-LE95%, reflecting its ability to incorporate spatially variable point-cloud precision and detect fine-scale geomorphic adjustments that may be reduced or smoothed during raster-based differencing. These results show that early post-installation change was spatially variable and included localized lowering and accretion, emphasizing that short-term adjustment should not be interpreted as long-term living shoreline performance and demonstrating the value of repeat sUAS-SfM surveys with uncertainty-aware change detection in low-relief coastal settings.