Understanding gully erosion development through geomorphological approach

This study aims to identify the gully erosion typology and development using a geomorphological approach. Gully geomorphology features were executed using combined photogrammetric approaches: aerial photography (unmanned aerial vehicle, UAV) and terrestrial photo data (structure from motion, SfM). The UAV data are used to identify the gully orientation, while SfM derives the geomorphological features in the gully dimensions. Five canopy-free gully erosion points were selected for the UAV-SfM data acquisition. Typically, SfM data offer higher resolution (0.11-0.57 cm) than UAV data (0.61-2.08 cm). Modelling using SfM can provide an in-depth illustration of gully dimensions such as rill erosion, scars, and cracks. The findings demonstrate that the gully depth and width are larger on the middle slope. This phenomenon is influenced by the strength of the flow and the silt transported by the water, which reaches a peak on the middle slope. The lower slopes have a solid form since the power of the flow weakens as it transports the accumulated silt from the upper and middle slopes. The study's findings can be relied on to guide communities in strengthening the gully body in the middle slope. Furthermore, the findings can be tested and adopted globally with comparable typologies.