Assessing the effects of external factors on sediment erosion and accumulation in an estuarine environment based on images from unmanned aerial vehicles: Namdaecheon, South Korea

Estuaries include dynamic patterns of channels, which serve as valuable habitat. The Namdae-cheon estuary is a closed estuary due to the natural dunes surrounding it, making monitoring particularly important. The use of unmanned aerial vehicles (UAVs) has considerable promise for monitoring dynamic areas such as the Namdae-cheon estuary. They are easy to use and can be implemented to obtain a high-resolution digital surface model (DSM) and georeferenced images. We monitored the Namdae-cheon estuary two times in a 1-month period (on November 20 and December 18, 2018). The estuary experienced significant morphological changes during the study period. The height of the sandbar sediment was reduced by about 30 cm, as revealed by DSM of difference (DoD) analyses. Sediment samples were also analyzed and used to explain the dominant factors influencing sedimentation in the estuary. By combining DSM data from UAV photos with sediment sample data, it was possible to explain the causal factors of morphological changes and infer the direction of sediment movement in the study area. Tidal factors, wind speed, and rainfall all influenced morphological changes and sedimentation. Overall, UAV photos and the resulting DSM, orthophotographs, and DoD provide abundant information for studies monitoring morphological changes.