Benchmark rock fall hazard assessment and safety concept for touristically developed alpine gorges (Höllentalklamm, Bavarian Alps).

The Höllentalklamm (Höllental Gorge) in Grainau is part of the main mountaineering route to the Zugspitze and with up to 2000 daily visitors a major tourist attraction in the Bavarian Alps. Following several recent rock fall events (up to 300 m³) the TU Munich collaborates with the local Alpine Club (DAV-GAP) to detect, assess and monitor rock fall hazards and to develop a benchmark safety concept for the Höllentalklamm. We combine multi-temporal terrestrial laser scanning, field mapping and the use of wireless sensor networks and evaluate the applicability of these methods for deeply incised alpine gorges.

In this study, we investigate a deeply incised and tectonically shaped alpine gorge in a well-researched mountain range (Wetterstein). In visibly accessible areas, multi-temporal terrestrial laser scanning is applied to (a) detect active rock fall areas, (b) identify hazardous objects pre-failure and (c) monitor potentially unstable parts of the rock face. Additionally, larger objects, such as a 600 m³ rock tower located directly above the track, are equipped with a redundant crackmeter system implemented in a wireless sensor network. Together with the DAV Garmisch-Partenkirchen, we are working on the development of safety procedures and the implementation of an automated early warning system. The first results show that terrestrial laser scanning is well-suited to detect post- and pre-failure rock falls above the level of detection, however, monitoring of small deformations remains a challenge. The crackmeters provide sub-millimetre deformation data of the rock tower and show generally stable conditions but a significant sensitivity towards external triggers such snow blasting in spring. Aside from that, direct rock fall hits hinder the sensor maintainace.

Here we show a benchmark rock fall hazard assessment and safety concept for Alpine gorges with high safety demands providing four years of data. This work helps to evaluate the applicability of well-established monitoring techniques in confined and inaccessible terrain (deeply incised gorges).