Erosion processes in calanchi in the Upper Orcia Valley, Southern Tuscany, Italy based on multitemporal high-resolution terrestrial LiDAR and UAV surveys

Abstract

A 125,000m2 calanchi badland in the Province of Siena (Tuscany) was monitored with an unmanned aerial vehicle (UAV) and terrestrial laser scanning over the period of one year. TLS (terrestrial laser scanning) was carried out on two sample slopes, whereas the image acquisition of the UAV covered the entire catchment. In combination with ground control points, the UAV images were used to create orthophotos and 3D point clouds using the Structure from Motion (SfM) software Photoscan. The TLS surface models indicate seasonal differences in erosion and deposition. The surface change measured with SfM showed nearly 6.700m3 of net material loss, resulting from 8.700m3 erosion and 2.000m3 deposition. These values reveal a mean annual surface lowering of 5.3cm for the catchment. Additionally, several geomorphological processes, such as rill erosion, slope wash and translational slides could be detected in the one-year monitoring period. A comparison of TLS and SfM results showed differences in the calculated volumes of mobilised material. These discrepancies resulted from shadowing effects and low point densities of the TLS point clouds.