Towards a simple predictive erosive debris-flow model calibrated with contrasting environmental settings

Debris flows are fast, hazardous and massively erosive mass movements that can cause severe danger to infrastructure and have been responsible for a significant number of casualties in the last decades. The European and German Alps face an increasing frequency and magnitude of hazardous debris-flows due to more frequent rainstorms in a warming climate. While the erodibility of the channel bed is a major contributor to the magnitude of debris-flows and the effective erosion often represents more than 80% of the final volume (Dietrich and Krautblatter, 2019) which, it is not or not sufficiently implemented in present debris-flow models.

Here, we present a concept of a simple predictive erosive debris-flow model calibrated with two erosive debris-flow events in the German Alps in June 2015. Both torrent channels were recorded with terrestrial laser scans and compared with an airborne laser scan performed in 2007. The detected geomorphic change was subdivided by same-length segments and correlated with modelled flow velocities at the cross-sections between the segments. The flow velocity at the cross sections was calculated by individual RAMMS Debris Flow simulations for every segment, each including the cumulated erosion volume of the sections upstream as well as the initial volume estimated from a rainfall-runoff calculation. As a result, we obtain a linear relationship between flow velocity and mean erosion depth, which can be used in a predictive debris-flow model to iteratively calculate the entrainment in every channel segment.

By analysing further geological and topographical debris-flow settings, we aim to create an inventory of different catchment characteristics and calibrate the model to various dimensions and properties. This would enable enhanced magnitude predictions of anticipated erosive debris-flows in comparable catchments by a fully forward-modelling approach.

Reference:

Dietrich, A. and Krautblatter M. (2019): Deciphering controls for debris-flow erosion derived from a LiDAR-recorded extreme event and a calibrated numerical model (Roßbichelbach, Germany). Earth Surface Processes and Landforms 44: 1346-1361, doi: https://doi.org/10.1002/esp.4578.