Gully-landslide interaction study by coupling LiDAR and SfM high-resolution DEMs

Abstract

<p>Landslides and gullies are essential drivers of land degradation, especially when interacting through positive and negative feedback loops. In hilly non-forested areas, landslides can be triggered by gullies, and gully follows landslides, generating positive feedback geomorphic systems at hillslope scale level. Landsliding can also restrict gully incision through generalized bank failure, especially in clayey lithology, causing negative feedback geomorphic systems at the same scale.<br>High-resolution topography is needed in order to map the morphologies produced by the above-mentioned hillslope geomorphic systems.Repeat high-resolution topography is also able to pinpoint small-scale evolution shaped by the processes that were discussed above. The high-resolution topography is especially powerful in geomorphological analysis of hillslopes in non-forested and sparse vegetated hilly areas.<br>We present the coupling of LiDAR and Structure from Motion (SfM) high-resolution DEMs for mapping and geomorphic change detection analysis of a hillslope geomorphic system that includes interacting landslides and gullies with both positive and negative feedbacks.<br>The LIDAR data from 2012 (2 to 6 points per square meter) and the SfM data from 2019 (5 to 10 points per square meter) are used for creating high-resolution topography that represents the base for both geomorphological mapping and geomorphic change detection. This advanced remote sensing data is obtained and processed using various methods (co-registration, geomorphic change detection, geomorphometric mapping) in order to map and understand gully and landslide interactions along a hillslope from Moldavian Plateau, Northeastern Romania. The additional ortophoto-imagery obtained through the SfM process is usable in the geomorphological mapping based on the high-resolution DEM.<br>The results show the presence on the same hillslope of both positive and negative feedback geomorphic systems that have important control on soil erosion and land degradation. The shallow retrogressive landsliding is favoring soil erosion, but the hummocky topography predisposes to surface water and sediment dysconnectivity. Piping appears in connection with the subsurface routing of water, a situation that favors gully initiation and development. Gully development will trigger landslides, but on sectors, gully evolution is stopped by the bank failure through landsliding. The dry climate does not favor connectivity, and gully evolution might stop. Land use and anthropogenetic impact introduce disequilibrium that restarts gully<br>evolution. In this geomorphological context, the land degradation is amplified by the land use (intensive degraded pasture), anthropic modifications (dirt roads), and the presence of piping due to the lithology.<br>In the presented study, advanced remote sensing is used for the analysis of landslide and gully interaction that favor land degradation. We show how remote-sensing based high-resolution topography both in non and multitemporal setting allow the characterization of geomorphic systems at the hillslope scale.</p>