Quantifying Morphodynamic Change of the Bay-Marsh Boundary by Integrating UAS Photogrammetry and Boat-Mounted Echosounding

The bay-marsh boundary is a dynamic topographic feature. Advances in remote sensing provide cost-effective, high-resolution mapping technologies to detect change at fine scales. However, many questions remain about how to best apply these technologies and quantify change at bay-marsh boundaries. We combine UAS photogrammetry and boat-mounted echosounding to map the bay-marsh boundary over two consecutive years and use a previously collected Lidar dataset for decadal timescale comparisons. We evaluate accuracy, lateral and volumetric change rates, and how this approach compares to traditional methods of quantifying change. Results indicate an elevation uncertainty of 0.07 m for the topobathymetric DEMs. Volumetric erosion rates between marsh shorelines were -0.78 0.22 and -0.25 0.15 m3m-1yr-1 at an 8-year and annual sampling interval respectively. Lateral erosion rates were -1.57 0.15 and -1.54 0.07 m yr-1 at an 8-year and annual sampling interval respectively and were weakly correlated with volumetric change rates, even within morphologically similar sections of the marsh edge. Measured volumetric change rates of the marsh edge were reasonably estimated with limited vertical data at decadal timescales, suggesting that this change could be approximated with an RTK system. However, high-resolution mapping remains essential for assessing annual, event-driven, or small-scale change.