Landslide susceptibility analysis with a heuristic approach in the Eastern Alps (Vorarlberg, Austria)

doi:10.1016/j.geomorph.2006.10.032

Geomorphology

Volume 94, Issues 3–4, 15 February 2008, Pages 314-324

https://doi.org/10.1016/j.geomorph.2006.10.032 Get rights and content

Abstract

The aim of the study is landslide hazard assessment carried out on a working scale of 1:25 000. The study area within the Northern Calcareous Alps was geologically and geotechnically mapped in order to identify causes and mechanisms of active mass movements. The field surveys were digitised by a Geographical Information System and divided into data layers. The geological units were classified according to their geotechnical properties. All layers were converted into grids and spatially analysed together with a Digital Elevation Model. Comparing the layers with the inventory of active landslides, the prevailing factors leading to sliding movements were identified. Because of the complex tectonic setting and the small number of active landslides, a statistical method of hazard assessment was not applicable. Using the heuristic approach of an index method, the data layers of geotechnical class, bedding conditions, tectonic layouts, slope angles, slope orientations, vegetation and erosion were analysed. The susceptibility of each layer has been evaluated with help of bivariate statistics. The layers have been weighted with indices due to their importance iteratively and were combined into a landslide susceptibility map.

Introduction

The region of the Eastern Alps is intensively used for settlement, forestry and tourism. The high relief energy and intensive physical weathering lead to various types of mass movements, imposing hazards to people, buildings and infrastructure. Because even small events can cause severe damage, reasonable land-use planning is able to prevent or minimise financial and human loss. The Department of Applied Geology (AGK) of the University of Karlsruhe (TH) in cooperation with the Vorarlberg Federal Government and the Inatura Museum in Dornbirn is working on landslide risk assessment at a medium scale (“Geohazard Map Vorarlberg”). Two study areas within the Bregenzerwald and the Hochtannberg/Arlberg region were geologically and geotechnically mapped to identify causes and mechanisms of active mass movements.

According to Aleotti and Chowdhury (1999), two main general approaches to landslide hazard assessment are distinguished: qualitative and quantitative methods. Within a quantitative method, mechanical or statistical models for slope failures are used to predict landslides (e.g. Carrara, 1983, Jäger and Wieczorek, 1994, Donati and Turrini, 2002, Zhou et al., 2003). This approach is difficult to use for a wide area, because mechanical parameters can not be extrapolated on a regional scale (Aleotti and Chowdhury, 1999). The second approach is the qualitative (heuristic) evaluation of actual landslides compared with characteristics of geomorphology or geology (e.g. Stevenson, 1977, Anbalagan and Sing, 1996, Reiterer, 2000, Ayalew et al., 2004). This method is strongly dependent on the experience of the surveyors, but it is the only practicable approach for landslides caused by different mechanisms.

Two methods for hazard assessment were applied in the study areas: a heuristic approach on basis of an index method and a quantitative approach with the aid of neural networks. Evaluating the different results with field data it was found out that the number of events and the density of landslides in the study areas did not allow a quantitative approach. Therefore it was decided to apply the heuristic approach with aid of a Geographic Information System (GIS) using grid data (Kassebeer and Ruff, 2003). When possible, factors leading to landslides were analysed with bivariate statistics to confirm the heuristic assumptions. In agreement with the Federal Government a method of landslide susceptibility assessment was proposed, which should be applicable to the whole territory of Vorarlberg.

Section snippets

Regional setting

One of the study areas is situated in the eastern part of Vorarlberg, the so-called Hochtannberg/Arlberg region (Fig. 1). It comprises an area of 115 km² and is divided into the two main valleys of the Bregenzerache and Lech rivers. The morphology is alpine with steep slopes of bare rocky outcrops. The highest peak of this region is the Trittkopf (2720 m.a.s.l.), whereas the central Lech valley has its deepest point at 1265 m.a.s.l.. The population of about 1900 inhabitants belongs to three

Spatial analysis

107 rock and soil slides were gathered in an inventory map and analysed using a GIS (ArcGIS 8.2). In the GIS the surface areas of main scarps and sliding bodies are recorded seperately. As an approximation the surface surrounded by the crown was used as the depletion zone and the sliding body was defined as the accumulation zone. Both zones combined give the total area (surface extent) of the slide.

Table 1 and Fig. 3 contain some facts about the type and number of slides in the study area. The

Results

Now the susceptibility could be calculated for each cell of the study area. Mathematically each factor is weighted by multiplying of all indices (2) and summing up of all factors (3): $I_{factor} = I_{1} \times I_{2} \times I_{3}$ $Susceptibility = I_{Slope} + I_{Aspect} + I_{Geotech . Class} + I_{Bedding} + I_{Faults} + I_{Vegetation} + I_{Erosion}$

where I₁ is the Index of the layer, I₂ is the Index of the layer within the group and I₃ is the Index of the group.

The calculation resulted in a susceptibility distribution between 0.15 and 0.92 (Fig. 7). To

Conclusion

The tectonic layout with folding and faulting at various scales leads to different types of sliding mechanisms in the study area. Some of these could not be detected with GIS and statistical analysis. Because of this problem and the low density of slides in the study area, it was not possible to use a quantitative method of hazard assessment. Consequently we concentrated on a susceptibility analysis of the slides, induced by geology, morphology and environment.

With a heuristic approach the

Acknowledgements

First of all, the authors thank the geological surveyors Nadine Hawelka, Georg Hils, Christian Schanz and Marcel Fulde. Furthermore we would like to thank the Inatura Museum in Dornbirn for the funding of the project, the Vorarlberg Federal Government for the cooperation and the Federal Surveying Office of Austria (BEV) for the data. Special thanks go to the revisionists Petra Metz, Joachim Rohn and Dominik Ehret. At last we want to thank Paolo Budetta for a constructive and very detailed

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Landslide susceptibility analysis with a heuristic approach in the Eastern Alps (Vorarlberg, Austria)

Abstract

Introduction

Section snippets

Regional setting

Spatial analysis

Results

Conclusion

Acknowledgements

Eng. Geol.

Tectonophysics

Eng. Geol.

Landslide hazard assessment: summary review and new perspectives

Bull. Eng. Geol. Environ.

Landslide susceptibility mapping using GIS-based weighted linear combination, the case in Tsugawa area of Agano River, Niigata Prefecture, Japan

Landslides

Multivariate methods for landslide hazard evaluation

Math. Geol.

Landslide types and processes

An objective method to rank the importance of the factors predisposing landslides with the GIS methodology — application to an area of the Apennines (Valneria; Perugia, Italy)

Eng. Geol.

Late Jurassic to Eocene palaeogeography and geodynamic evolution of the Eastern Alps

Mitt. Österr. Geol. Ges.