Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

Abstract

Abstract. Predicting potential deposition areas of future debris-flow events is important for engineering hazard assessment in alpine regions. For this, numerical simulation models are commonly used tools. However, knowledge of appropriate model parameters is essential but often not available. In this study we use two numerical simulation models, RAMMS-DF (Rapid Mass Movement System – Debris Flow) and DAN3D (Dynamic Analysis of Landslides in Three Dimensions), to back-calculate two well-documented debris-flow events in Austria and to compare the range and sensitivity of input parameters for the Voellmy flow model. All simulations are based on the same digital elevation model with a 1 m resolution and similar initial conditions. Our results show that both simulation tools are capable of matching observed deposition patterns. The best fit parameter set of μ [–] and ξ [m s−2] range between 0.07–0.11 and 200–300 m s−2, respectively, for RAMMS-DF, and 0.07–0.08 and 300–400 m s−2, respectively, for DAN3D. Sensitivity analyses show a higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This study shall contribute to the evaluation of realistic model parameters for simulation of debris-flows in steep mountain catchments and highlights the sensitivity of the models.

Impact of a Random Sequence of Debris Flows on Torrential Fan Formation

“…The RAMMS-DF model includes two options for the input debris flow definition that were also used in this study, namely, a block release option and an input hydrograph option. A detailed RAMMS model and debris flow module description can be found in references [9,13,16,[18][19][20][21][22][23]. In this study we investigated two case studies, namely, a real torrential fan named the Suhelj fan (described in Section 2.2) and artificial terrain with a constant slope (described in Section 2.3).…”

“…All model parameters were kept constant during all 62 model runs for the Suhelj fan and artificial terrain case studies (percentage of total momentum, 5%; dump step, 50 s; a second-order numerical scheme was used; density, 2000 kg/m 3 ; lambda, 1; H cutoff, 0.000001 m; input angle did not change during the simulations). Based on the literature review (e.g., [10][11][12][13]18,29,30]), different sets of Voellmy parameters were used (Table 1). It should be noted that some of the cases shown in Table 1 could be regarded as unrealistic for the alpine environment (e.g., .…”

“…It should be noted that some of the cases shown in Table 1 could be regarded as unrealistic for the alpine environment (e.g., . According to the literature (e.g., [10][11][12][13]18,[29][30][31]), Cases 1 and 3 could perhaps be regarded as the most relevant for the selected case study (i.e., the Suhelj fan). However, we decided to also carry out simulations for other cases since these could be of interest for researchers dealing with other environments.…”

“…This module was developed to simulate the runout of muddy and debris-laden flows in complex terrain. Since its release in 2011, it has been applied for different terrains in Switzerland (Illgraben and Spreitgraben [10]; Richleren, Minstigerbach, Glyssibach and Varuna [11]; Meretschibach and Bondasca [12]), Austria [13], Italy (Southern Apennines [14]), France (Barcelonnette [15,16]), and Norway [17], among others.…”