Abstract: The aim of the project «Geohazard Map Vorarlberg» was hazard and risk assessment
using Geographic Information Systems (GIS) at a regional scale. A transparent
method of hazard assessment should be documented, which is using mainly
existing data and is applicable for other alpine regions.
Geological and geotechnical maps have been created to identify causes and
mechanisms of active mass movements. The study areas lie within the geologic
units of Molasse, Helvetikum, Rhenodanubian Flysch und Northern Calcareous
Alps. Quaternary sediments, like slope debris and moraines, are of local importance.
The active mass movements were gathered in a landslide inventory and
digitised via ArcGIS together with the maps. For the hazard assessment the formations
were classified according to their lithological behaviour. All data were
analysed as grids with a cell size of 25 meters.
Two types of mass movements imply a geological hazard: sliding and falling.
Because of the different mechanical behaviour, both types have to be considered
separately at first. In reference to the regional scale, the susceptibility to
landslides was divided into five categories (very low, low, medium, high, very
high). The hazard assessment for slides was accomplished using an index
method. Comparing the preparatory factors to the landslide inventory with bivariate
statistics, susceptibility indices for the layers lithology, bedding, faults, slope
angle, aspect, vegetation and erosion were estimated. In a three step iterative
method the layers were combined into a susceptibility map. Hazard areas of
rockfalls were estimated with a cost analysis of the movement of rolling rock
samples. Potential source areas of falling material were extracted out of the
Digital Elevation Model. A cost grid was calculated on the basis of slope angle
and rolling friction. Interpreting the distribution of the cost calculation, a susceptibility
map was constructed.
In relation to landuse and infrastructure a vulnerability map was created also
according to five different classes. The overlay of susceptibility and vulnerability
leads to the risk map. In this map, the areas of increased risk are exposed objectively
on a regional scale. The constructed maps give an insight into the hazard
situation for users without detailed knowledge about geology. Therefore these
maps represent a useful tool for spatial planning. Local population can be informed
about geologic hazards of their homelands, leading to a decrease of risk on
the long run.
The studies were financed by the Federal Government of Vorarlberg and the
Inatura Museum Dornbirn.
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.
Abstract: In this paper a tool for semi-quantitative susceptibility assessment at a regional scale is presented which is applicable at areas with complex geological setting. At a study area within the Northern Calcareous Alps geotechnical mappings were implemented into a Geographical Information System and analysed as grid data with a cell size of 25 m. The susceptibility to sliding and falling processes was considered according to five classes (very low, low, medium, high, very high). Susceptibility to sliding was analysed using an index method. The layers of lithology, bedding conditions, tectonic faults, slope angle, slope aspect, vegetation and erosion were combined iteratively. Dropout zones of rockfall material were determined with help of a Digital Elevation Model. The movement of rolling rock samples was modelled by a cost analysis of all potential rockfall trajectories. These trajectories were also divided into five susceptibility classes. The susceptibility maps are presented in a general way to be used by communities and spatial planners. Conflict areas of susceptibility and landuse were located and can be presented destinctively.
Abstract: Innerhalb des Projektes âGeorisikokarte Vorarlbergâ wurden mehrere Gebiete in Vorarlberg geologisch und geotechnisch kartiert. Aktive Hangrutschungen wurden gesammelt und mit verschiedenen Datenebenen auf Rasterbasis verglichen. Mithilfe einer Index-Methode wurden die Faktoren Hangneigung, Hangrichtung, Hangwölbung, Geotechnische Klasse, Nähe zu tektonischen Störungen, Vegetation und Erosion zusammengefasst. Die so gewonnene Grunddisposition (Suszeptibilität) für Rutschungen wurde in fünf Klassen (sehr gering, gering, mittel, hoch, sehr hoch) aufgeteilt und auf einfache Weise für ein breites Anwendungsspektrum dargestellt. Die Ergebnisse dieser Analyse werden anhand dreier unterschiedlicher Arbeitsgebiete vorgestellt und aufgrund der Geländeerfahrungen bewertet. Es sollte geklärt werden, ob diese qualitative Methodik ausreichend und sinnvoll ist, eine Suszeptibilitätskarte für ganz Vorarlberg zu erstellen.
Abstract: The aim of the project âGeorisikokarte Vorarlbergâ was landslide susceptibility assessment at a regional scale. Using a qualitative approach, the susceptibility to sliding and falling movements was analysed according to five categories (very low, low, medium, high, very high). All data layers were handled as grids with a cell size of 25 m. The susceptibility to sliding was analysed with an index method based on the data layers slope angle, slope aspect, slope curvature, lithology, distance to tectonic faults, vegetation and erosion. The trajectories of potential rockfall blocks were compared using a cost analysis based on rolling friction. The methods were tested at three different study areas in Vorarlberg and calibrated with a landslide inventory. Special focus was laid on the presentation of the results. The susceptibility map should be understandable for spatial planners as well as local people, municipal employees and politicians.
