Due to the effect of global climate change the occurrence of debris flows and rock falls has increased. In response to the negative effects the development of new mitigation measures against natural hazards has become a prime importance. During the last two decades flexible rockfall protection systems were continuously developed with energy absorption capacities up to 5'000 kJ. In 2005, first flexible barriers against debris flows, which are having greater than 5'000 kJ impact energy, were installed in a large creek, called Illgraben, in Canton Wallis (Switzerland). This research project was in collaboration with the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). The installed test barriers successfully stopped several debris flows and they could be over flown by several 10'000 m3 of material without any damaging impact. The measured flow parameters allow a formulation of a load model for debris flow filling and overflowing process of ring-net barriers. The important dimensioning aspects for flexible debris flow barriers, the mode of installation and different kind of application will be explained in this paper. Along with an outlook into the ongoing research project of adapting and developing flexible barriers against shallow landslides.
Conventional mitigation measures for debris flows consist of heavily reinforced concrete sometimes combined with heavy steel or wood components. The disadvantage of these systems is reflected by less permeability leading to stronger buildings resulting in high costs for material and difficulties in logistics due to poorly accessible mountainous regions. One advantage of ring-net barriers in comparison to traditional concrete structures is that the ring-net barriers are light and flexible and can easily be installed in remote regions by transporting the system with helicopters. Furthermore, the maximum impact forces are reduced by long braking distances and flexible deforming structures. The stopping process has already been studied using similar barriers intended as protection against rockfall, woody debris in rivers or small snow slides. However, the load distribution over the barrier for debris flows is different than other applications. Thus, corresponding research is necessary, and a new project was initiated in 2005 that combines the results from full-scale field tests and laboratory experiments with numerical simulation results, giving new insight into the flow barrier interaction during and after a debris flow impact. Also a so called multi level barrier application to stop bigger flow volumes step by step was researched within this project (Speerli et al. 2010). In 2007, the first installation of three multilevel barriers was implemented in the Merdenson gully, Switzerland (Speerli et al. 2010). A few months after the installation the three barriers got filled by a debris flow. Since 2007, several debris flows have overtopped this multi level barrier system successfully. For ongoing research studies, these barriers stayed filled in the torrent to study their long term behavior as a check dam application. A further application of adapted flexible barriers is the installation in open hill sides as a direct property protection measure for example; houses, hydropower plants and transportation infrastructure.
