Quantifying reach-scale erosion and deposition using unmanned aircraft system (UAS) photogrammetry and airborne lidar

Monitoring erosion and deposition along river corridors as channels evolve over time provides an understanding of geomorphic processes at work in the river system. Additionally, long-term monitoring of river corridors can lead to characterizing the rate of bank erosion and fine sediment loading, temporal patterns of bed load sediment transport, and sensitivity of the river channel to high discharge events. In this study, we evaluated the ability of unmanned aircraft system (UAS) based photogrammetry to capture fine-scale topography of a river corridor and monitor rates of erosion and deposition along the corridor. A fixed-wing UAS was used to survey a 1-km reach of the New Haven River in central Vermont, located in the temperate northeastern United States. This particular reach was selected because it exhibits instability due to its sensitive landscape position at the transition from mountainous headwaters to the valley bottom and history of watershed and channel disturbances. Digital elevation models (DEMs) and DEMs of difference (DoDs) were generated from repeat UAS surveys performed annually between 2015 and 2018. UAS-based DEMs were compared to existing airborne lidar data from 2012 and GPS-surveyed ground control points to assess the accuracy of the automated DEM generation process. DoD analysis provided annual quantification of bank erosion and also revealed annual variation in the volumes of erosion and deposition along the river reach. Erosion and deposition rates were compared with geomorphic assessments of the river to assess the sediment transport regime of the river.