An early warning system for landslides

New technology allows permanent observation of endangered mountain areas

Devastating landslide in Doren 2007 © Friedrich Boehringer / CC by-sa 2.5
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As a result of climate change in the Alps and other high mountains more and more slopes threaten to slip - with fatal consequences for people and infrastructure. Permanent monitoring of all areas at risk has so far failed due to excessive costs and effort. Munich-based geo-researchers have now developed a low-cost system that permanently monitors slopes using multiple technologies, evaluates changes and warns the affected municipalities of impending landslides at an early stage. The scientists themselves hope that the long-term measurements will lead to a better understanding of these natural phenomena.

Doren in the Bregenzerwald, February 2007: At a length of 650 meters, a slope breaks away, massive earth masses slide into the depths. The nearest houses are just near the 70-meter-high demolition edge. The near-disaster is not an isolated case. In the past few years, geologists have increasingly observed so-called labile soil masses in the Alps and other high mountains that slide on slopes and glide unstoppably on a stable surface in the direction of the valley.

The reason for this, according to the scientists, is above all stronger rainfall and snowmelt due to climate change, which softens the soil and at the same time makes it heavier.

Expensive equipment

Identifying potentially dangerous mountain flanks is not too difficult. Many have been unstable for centuries, traditions bear witness to past misfortunes. In the Alpine countries, geological recordings are also available that reveal risk candidates. A permanent monitoring of all troubled masses, however, was so far impossible. In order to detect movement, experts had to drill probes into boreholes and measure surface markers.

However, installing these devices permanently is usually simply too expensive. Thus, the inspectors can check only at intervals and gain only selective knowledge about the inner workings of the slopes. display

Video tachymeter that detects movements of natural targets with a laser scanner and camera. Research Group alpEWAS

Components from the bar

Researchers from the Technical University of Munich (TUM) and the University of the German Armed Forces Mnchen have now decisively developed geosensors and combined them with control software to create an early-warning system that is both flexible and cost-effective pft. They also drill into the ground in several places.

"However, we are using very simple coaxial cables, such as those of antenna cables, " says Professor Kurosch Thuro of the TUM Chair of Engineering Geology. Scientists use a simple but effective mechanism: when the upper layer of soil slips, the cable is squeezed at the transition to the immovable layer. A small transmission device on the surface registers this and forwards the information.

In addition, the engineering geodesists of the Bundeswehr University around Professor Otto Heunecke distribute sensors over the slope, whose position can be determined by means of GPS. Here, too, the challenge lay in achieving a measuring accuracy in the millimeter range with inexpensive "off-the-shelf" components in order to register even the smallest displacements.

New generation of measuring instruments

Third, the scientists are using a new generation of gauges, called video tachymeters, that work with a laser scanner and camera. In the past, when artificial reflectors had to be set up to measure the direction, distance and height of a target, today's devices also detect natural targets, such as rocks or tree stumps.

The researchers have now programmed the prototype of a manufacturer so that it also detects movements of any number of targets. The tachymeter records the structure of a rock, measures it regularly and registers changes. "If we do not have to set up reflectors, we'll save money again, " says Professor Thomas A. Wunderlich of the TUM Chair for Geod sie. "And we do not have to fear that they will be knocked over by grazing cows."

John Singer of the Department of Engineering Geology tests the data transmitted by the early warning system "alpEWAS" at a borehole on the Sudelfeld in Oberaudorf. Research Group alpEWAS

Dense network of observation points

With these three components, the scientists link a dense network of observation points over the slope. The data is brought together in a central database. The brain of the system evaluates the information along with other indicators, especially with weather data.

For three and a half years, the researchers have tested their development on the Sudelfeld in Oberaudorf in Upper Bavaria. There, a mountain flank moves and threatens several alpine pastures and a federal highway. "The data series shows us impressively what the Hang is experiencing, how precipitation and frost are felt, what happens mechanically, " says Thuro. "We now understand much more about this movement."

Evaluation of the data allows early warning

Therefore, scientists can better evaluate individual events. For example, when the slope slipped by four millimeters within a short space of time in May 2010, they knew that the initially small distance for this area was extraordinary and therefore worrying. Even more: the evaluation of the data even allows early warnings before the slope has even moved.

"Because we now know how rain falls there, we could set a limit, " explains Thuro. If the groundwater pressure exceeds a certain value, the system will alarm. "Then there are about two and a half days left between the rise of the level and a slope movement."

Lock endangered slopes

According to the researchers, affected communities can benefit directly from the system because it provides them with the data without any detours - translated into understandable diagrams and explanations. After an early warning, those responsible can, depending on the danger, block slopes, divert traffic or evacuate houses.

The researchers are now developing the system under the title "Early Warning System for Alpine Slopes" (alpEWAS) with two industrial partners to market readiness. The first interested parties have already reported, in Doren part of the system is even already in use. Not only for the users, but also for the science itself Thuro promises significant progress: "The more slopes we examine permanently, the more we understand larger relationships between individual events and the macroclimate in the mountains."

(Technical University of Munich (TUM), 07.04.2011 - DLO)