Real-scale measurements of debris-flow run-ups

Abstract

Rapid mass movements, such as debris flows, endanger alpine areas due to their destructive nature. In order to counteract these dangerous flows, it is necessary to design appropriate mitigation measures. A particular problem is the run-up of debris flows that impact on such structures. We provide in situ measurements of the run-up of three natural debrnis flows, each with multiple surges, in Gadria Creek, resulting from interaction with a mid-channel structure monitoring station. Four models were checked against data from other studies and the in situ measurements of the natural debris flows. The natural debris-flow measurements are all located in low Froude areas (Fr < 3) typical of Alpine granular debris flows. Sediment-laden pre-surges with Froude values greater than 2 produced the largest run-up factors in terms of run-up heights standardized to flow heights. Nevertheless, ensuing debris-flow surges exhibited a notable granular behavior and occurred at low Froude values. The findings indicate that the use of an energy conservation-based prediction model yields the most accurate estimates of the observed run-up factors. However, this smooth, gradual run-up can also be enhanced by preceding debris deposition and the formation of ramps. This can also prevent the formation of a reflection or shock wave, as assumed in models based on conservation of mass and momentum. These models have mainly overestimated the run-up factors of the observed debris flows.