Rheology of hail-debris flow and implications in flow mobility

Abstract

During 29-31 January 2021 (austral summer), an extreme storm event triggered catastrophic debris flows in central Chile (33-36°S). At small and precarious rural settlements in the commune of Malloa in central Chile, debris flows where triggered by a hailstorm. Hail-debris flows, with hail volume concentration near 10%-20%, caused 200 injured individuals and 73 damaged houses. In this study, hail-debris flows where modelled using the FLO2D. software, calibrated against flow velocities and flooded areas obtained from audio-visual records taken by local inhabitants (using cell phones) and a high-accuracy post-event topography obtained with a drone. Results suggest that hail content significantly reduces flow resistance compared to typical debris flows, thus increasing flow velocity, and run out. On the other hand, damage to infrastructure was more related to the materiality of the houses (precarious settlements) than to debris flow severity.