Empirical and dynamical modeling of debris flow events close to Longyearbyen and Svea, Svalbard

Abstract

Debris flows are a mountain slope hazard relatively well studied in densely populated mountainous regions, while few investigations have been done in Arctic permafrost regions. In order to get a better understanding of the processes involved in such an envi-ronment, this work focused on debris flow hazards in the mountains close to Longyear-byen and Svea on Svalbard, Norway, situated at 78°N.

A total of 52 debris flows were investigated in this Arctic environment between July and October 2011. The gathered slope information was embedded in highly accurate map data of the regions in order to get slope profiles of the debris flows. Those profiles were used for both empirical and dynamical modeling of the debris flow runout.

Empirical modeling showed that the mainland-calibrated αβ - model and NGI model may be used in order to get a better understanding about maximal runout of debris flows. In general, the output of the αβ – model and the NGI model fit the measured maximal runout.

Yet, Svalbard-calibrated models show a certain degree of improvement in accuracy. For engineering purposes, linear regressions for the longest runouts were performed. The models based on these regressions are advised to use for the evaluations of possible construction sites. The model assuming a deposition start angle of 20° achieved the best result with a standard deviation of 2.09°. This model is advised to use in future con-struction site planning.

The dynamical model RAMMS is a great tool for finding directions, although debris flow runouts are hard to estimate with the program.