The main highway between Scuol and Susch in the Engadin valley as well as the railway towards St. Moritz were threatened by avalanches on regular bases up to 2001, causing one fatality and 3 injuries in 1999 and many closures over the years.

In 2001 the authorities in charge of natural hazards started a pilot study in order to determine the efficiency of Wyssen Avalanche Towers to protect this highway. The engineering office KINDSCHI engineers & surveyors were engaged to supervise the project including a scientific study.

Three Wyssen Towers were installed in 2001 and five more in 2009 to protect the road, the railway, a hiking path and a cross-country track.

Initial situation

The Gonda avalanche was probably one of the last avalanches reaching the valley bottom approximately every fifth winter, where no structural measures had been installed by the year 2000. Due to the topographic conditions, permanent structural measures to reduce the risk would have resulted in an investment of around 40 million Swiss Francs. This would not meet the standards of cost/effectiveness ratio that is applicable in Switzerland.

Until winter 2000/01, avalanche control was carried out by means of a 12 cm mortar. In winter 1999, the Gonda avalanche reached the road, leading to one fatality and three injuries. The analysis of the avalanche starting zone showed, that the residual risk after using artillery could not be sufficiently reduced. This was the reason why even small amounts of new snow in the large bowl at the ridge of Piz Chapisun released, producing a major avalanche.

In the year 2000, the first Wyssen Avalanche Towers were tested. The regional road administration therefore launched together with the forest department a preliminary study for the system evaluation for protecting the highway in Engadin. In the year 2001, this study was presented to the Federal Office for Environment, which took over the larger part of the costs for the installation of Wyssen Towers. In addition, a scientific project control group was formed with Jörg Kindschi in the lead and team members from the WSL Institute for Snow and Avalanche Research SLF in Davos. The result showed that the Wyssen Avalanche Towers performed well after the first few initial problems have been solved. An excellent blasting effect was found particularly in the area around the towers.

The experiences in the first three test winters and afterwards as well, showed that the avalanche starting zones were inadequately covered. Areas to the side of the existing systems with avalanches coming from different starting zones as well could reach the road as well. This was the reason why the local avalanche control team applied to get more systems approved to extend the Gonda project.

Gonda Feb’14 (74)

Solution options

Before the additional towers were ordered, different concept options have been discussed, leading to different amounts of closure days per year.

The first concept option was the closures, the existing three avalanche towers and still using artillery. However, the long-term supply and operation of the artillery was not satisfactory, since the Swiss Army was about to take these weapons out of their program. Although helicopter bombing could still be considered for special cases as an additional tool, the problem was of course the dependability on the weather.

The second option was to increase the number of Wyssen Towers and completely cover all avalanche starting zones. Artillery could then be dismissed, leading to a better long-term durability of the concept. Technical systems, too, have limitations in their lifetime but since the electronic control or the deployment box can be replaced without having to change everything, the whole system can continue to work.

The third concept option was to increase the amount of Towers as in the second option, but in addition, a solution for the adjacent avalanche path Val Punia had to be found. Avalanche control for this path was not possible due to the risk of destroying protection forest, which meant the only possible measure would be snow fences. The area to cover with fences is around 10 ha with a slope gradient of more than 35° leading to 2000 m of fences and total costs of four million Swiss Francs.

Proposed solution

In order to assess the different options a benefit analysis with comparison of the cost effectiveness, durability, reduction of closure days and residual risk. The result with the best rating was concept option two.

From today’s point of view, it can be said that the first three Wyssen Towers installed in 2001 as well as the optimization in 2009 reduced the amount of closure days and the residual risk significantly and despite the investment, did not generate high overall costs.

Preventive avalanche release can be performed in any weather whenever the new snow reaches the critical level. The fact that the explosive detonates above the snow cover results in a huge effective range and high rate of positive releases of almost 90% according a study made by Jörg Kindschi. In addition, it requires less personnel resources to perform avalanche control with the result of faster, more precise and efficient activities.

New detection systems at service

Initially an infrasound detection system was installed to verify the result of the avalanche release actions. Because the experience with the supplier and as well with the performance was not satisfying, the road administration was looking for a new solution to verify the results.

Wyssen Avalanche Control AG has then received the order to deliver a radar. The company AlpuG from Davos has delivered a seismic detection system with geophones, which was to be upgraded with one additional geophone.

In addition, it was decided to design a web-based general platform where all different detection systems and all Wyssen Towers are displayed. After the first season, a second radar was installed and tested at the same location.

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