Analysing the Large-Scale Debris Flow Event in July 2022 in Horlachtal, Austria Using Remote Sensing and Measurement Data

Abstract

High-quality in situ measurements are essential for hazard assessment of debris flow events. However, precise data on debris flow triggering thresholds, accumulation volumes and spatial characteristics of large-scale events on catchment scale are scarce due to the rare occurrence of debris flows and the challenges of acquiring accurate data for a larger area. In this study, we present quantitative analyses of a single extreme debris flow event in the Horlachtal, Austria, triggered by local high-intensity short-duration precipitation events on 20 and 23 July 2022. Pre- and post-event airborne LiDAR (light detection and ranging) data with a high spatial resolution reveal that 156 different debris flow processes were initiated during these events, with accumulation volumes of up to approximately 40,000 m³. The calculated debris flow deposition volumes also show a power-law relationship with the total amount of rainfall in the respective debris flow catchments. The spatial appearance of the debris flows shows a concentration of processes in a particular area rather than a uniform distribution, suggesting a local nature of the triggering event. This is further supported by the measurements from three meteorological stations and four discharge gauges within the study area. The gridded area-wide INCA (Integrated Nowcasting through Comprehensive Analysis) rainfall data further point to a local convective event on 20 July 2022, with a maximum rainfall intensity of 44 mm/h.

Numerical Modelling and Sensitivity Analysis of the Pitztal Valley Debris Flow Event

“…Run-off generated failures generally have low solid concentration, while slope failure or earthquake generated debris flow are typically dominated by the solid proportion. Finally, many past studies [36][37][38][39] have reported the volume of landslide material ranging from hundreds to million cubic meter, it is of interest to examine its impact on the study area. For sensitivity analysis, the basal friction angle is varied from 1 • to 20 • , the solid fraction from 0.25 to 0.85, and the initial debris volume from 4500 to 60,000 m 3 .…”