Enhanced mapping and modeling of multiple debris flow by lidar-based fixed wing UAV surveying

Abstract

Debris flows are a major geo-hydrological hazard in areas with steep slopes and unconsolidated deposits. Accurate characterization of source areas and flow paths is essential for hazard assessment and for planning mitigation measures. In contexts where initiation zones are distributed across multiple slopes or small catchments, traditional terrestrial surveys or multirotor UAV techniques are limited in spatial coverage and continuity. To overcome these limitations, this study proposes a methodological approach based on fixed-wing UAVs equipped with LiDAR and high-resolution cameras, aimed at the synoptic mapping of multiple debris flow channels and the quantitative assessment of morphological changes. Survey campaigns enabled the generation of high-resolution Digital Terrain Models (DTMs) and the derivation of elevation difference models using GIS-based techniques, allowing the estimation of eroded and deposited volumes, the delineation of source areas, and the identification of main flow paths through flow accumulation and watershed analysis algorithms. Analysis of multitemporal surveys, conducted a few months apart, revealed that the most significant erosional processes are concentrated in the upper portions of slopes, with average erosion depths of several tens of centimeters and localized incisions exceeding 5–10 meters. Delineating of flow lines and drainage basins also allowed mobilized volumes to be correlated with specific channels, identifying basins with the highest reactivation potential. The use of fixed-wing UAVs proved particularly effective for covering large areas within short operational times, ensuring centimeter-scale spatial resolution even at poorly accessible sites. Integration with LiDAR technology allowed for the accurate reconstruction of ground morphology in densely vegetated areas, providing a solid basis for subsequent numerical simulations of debris flow propagation. These simulations enabled the estimation of potential inundation scenarios and supported the design of structural mitigation measures. The results show that the integrated UAV–LiDAR and numerical modeling approach constitutes an effective tool for the geomorphological characterization of multiple basins affected by debris flows, providing quantitat.