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.
