Abstract
Abstract. Debris flows cause an average € 30 million damages and 1-2 fatalities every year in Austria. Detailed documentation of their extent and magnitude is essential for understanding, preventing and mitigating these natural hazard events. The recent development of unmanned aerial systems (UAS) has provided a new possibility for on-demand high-resolution monitoring and mapping. Here, we present a study, where the spatial extent and volume of a large debris flow event were mapped with different UAS, fitted with commercial off-the-shelf sensors. Orthophotos and digital terrain models (DTM) were calculated using structure-from-motion photogrammetry software. Terrain height differences caused by the debris flow in the catchment and valley floor were derived by subtracting the pre-event airborne laser scanning (ALS) DTM from a post-event UAS-DTM. The analysis of the volumetric sediment budget showed, that approximately 265,000 m³ material was mobilised in the catchment, of which 45,000 m³ settled there; of the material, which reached the valley floor, 120,000 m³ was deposited, while another 10,000 m³ was eroded from there. The UAS-results were validated against ALS data and imagery from a traditional manned-aircraft photogrammetry campaign. In conclusion, the UAS-data can reach an accuracy and precision comparable to manned aircraft data, but with the added benefits of higher flexibility, easier repeatability, less operational constraints and higher spatial resolution.
Highlights
Debris flows are described as ‘rapid, gravity-induced mass movements consisting of a mixture of water, sediment, wood and anthropogenic debris that propagate along channels incised on mountain slopes and onto debris fans’ (Gregoretti et al, 2016)
The objective of this paper is to present the use of unmanned aerial systems (UAS)-data to map the extent and calculate the volumetric sediment budget of a debris flow event, i.e. the total volume of eroded and deposited material in the catchment and valley floor
Prior to the UASflights, 30 ground control points (GCP), consisting of 0.4 x 0.4 m black and white checkered wooden boards were placed at predefined locations in the catchment and valley floor areas of interest (AOI), which were not affected by the debris flow
Summary
Debris flows are described as ‘rapid, gravity-induced mass movements consisting of a mixture of water, sediment, wood and anthropogenic debris that propagate along channels incised on mountain slopes and onto debris fans’ (Gregoretti et al, 2016). The development of novel computer vision techniques (structure-from-motion) and their implementation into commercially available software packages (e.g. Agisoft Photoscan Pro) have reduced the requirements for the recorded data (Vander Jagt et al, 2015; Turner et al, 2012) This development makes high-performance algorithms for 3D-processing more readily available to the UAS-community (Mancini et al, 2013; Hugenholtz et al, 2013). The objective of this paper is to present the use of UAS-data to map the extent and calculate the volumetric sediment budget of a debris flow event, i.e. the total volume of eroded and deposited material in the catchment and valley floor.
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