Application de la méthode des géotypes à la cartographie des secteurs de protection des eaux souterraines ainsi qu'à la détermination de la susceptibilité aux instabilités de versants

The aim of this study is to develop new methods for landslides mapping and water resources protection and management using geotypes and GIS. The first part of this report deals with the conception and the use of a new methodology for groundwaters’ protection areas delimitation. This study was carried out as part of an assignement for Canton de Vaud ; the results obtained for the Morges pilot area are already applied. The second part introduces the bedrock of a new method for landslide susceptibility mapping ; it involves the designation of mains hydrogeological factors for unstability predisposition, in situ method of estimation of these factors and, to finish with, the development of a sketch methodology and its implementation to eight sites

Apport des SIG pour la modélisation géologique tridimensionnelle: application à l'évaluation de la prédisposition aux instabilités de versants

The aim of this project is to introduce the bedrock of a new method for landslide hazard mapping; based on instability predisposition assessment, it involves the designation of main factors for landslide susceptibility, their integration in a GIS to calculate a landslide predisposition index and the implementation of new methods to evaluate these factors; to be competitive, these process will have to be both cheap and quick

Using geotypes for landslide hazard assessment and mapping: a coupled field and GIS-based method

Switzerland is exceptionally subjected to landslides; indeed, about 10% of its area is considered as unstable. Making this observation, its Department of the Environment (BAFU) introduces in 1997 a method to realize landslide hazard maps. It is routinely used but, like most of the methods applied in Europe to map unstable areas, it is mainly based on the signs of previous or current phenomena (geomorphologic mapping, archive consultation, etc.) even though instabilities can appear where there is nothing to show that they existed earlier. Furthermore, the transcription from the geomorphologic map to the hazard map can vary according to the geologist or the geographer who realizes it: this method is affected by a certain lack of transparency. The aim of this project is to introduce the bedrock of a new method for landslide hazard mapping; based on instability predisposition assessment, it involves the designation of main factors for landslide susceptibility, their integration in a GIS to calculate a landslide predisposition index and the implementation of new methods to evaluate these factors; to be competitive, these processes have to be both cheap and quick. To identify the most important parameters to consider for assessing slope stability, we chose a large panel of topographic, geomechanic and hydraulic parameters and tested their importance by calculating safety factors on theoretical landslides using Geostudio 2007®; thus, we could determine that slope, cohesion, hydraulic conductivity and saturation play an important role in soil stability. After showing that cohesion and hydraulic conductivity of loose materials are strongly linked to their granulometry and plasticity index, we implemented two new field tests, one based on teledetection and one coupled sedimentometric and blue methylen test to evaluate these parameters. From these data, we could deduce approximated values of maximum cohesion and saturated hydraulic conductivity. The hydraulic conductivity of fractured rocks was obtained from the analysis of their geometrical properties (fractures density, aperture size and orientation). The other factors were extracted from DEM and hydrologic mapping. Then, we merged these parameters into three groups corresponding to three families of factors (gravitational, hydrodynamic I based on hydraulic conductivity contrast between superficial loose material and hard rock substratum and hydrodynamic II related to susceptibility to suffosion). We added a fourth factor related to the predisposition of the geotype (new classification for geologic formations, based on genetic standards for loose material and on lithologic standards for hard rock) to slope instability processes: the latter enabled us to integrate attributes proper to each geotypes (over-consolidation for ground moraines, stratifications for glaciolacustrine deposits, etc...) and which would be long and complex to integrate to a GIS. Afterward, we implemented an ArcGis® toolbox allowing to obtain automatically cohesion, hydraulic conductivity, saturation and slope from field parameters (granulometry, plasticity, fracturation, geomorphology and drainage) and DEM and to calculate geotype, gravitational, hydrodynamic I and hydrodynamic II factors; combining them, we led to a landslide susceptibility index. To know the relative importance of these four factors, we tried different weightings on four areas in different geologic contexts of Switzerland (flysch, molasse, crystallin) and of different sizes (from 0.1 to 2.5 km2). Finally, we applied this methodology (from field survey to GIS operations) to five other sites in Switzerland to check its validity: in flysch and molassic contexts, more than 90% of actual landslides were classified as “very susceptible to slope instability”. In Triassic area, more than 50% of the actual unstable areas were classified as "stable", which is not satisfying:in this case, it should be necessary to integrate another layer of data to take into account dissolution and plasticity of Triassic formations. The main assets of this new method are that the integration of field measurements in GIS provides for a good transparency in the landslide susceptibility index attribution and that the use of geotypes classification enables to use this method in most of European contexts

GIS-based method for groundwater management and protection: geotypes serving 3D applications

Sustainable management of underground natural resources is more and more a worthwhile topic. In particular, worrying about groundwater protection becomes imperative. Taking into account the increase of incompatibilities between water conservation and the use of other underground resources, the Geolep laboratory brought one of its research axes around to new methods for groundwater resources assessment and management. As these methods have to be as transparent as possible, we implemented a GIS to use standardized protocols to realize new maps of groundwater protection areas and resources index and, in a second step, to determine where it should be possible to install geothermal heat pumps without endangering drinkable water resources (OFEV, 2009). These methodologies are both based on the use of the geotypes, which is a new classification for geological formations (Parriaux and Turberg, 2007); it involves the use of genetic standards for loose material (e.g. lodgement till) and lithologic standards for hard rock (e.g. sandstone). Forty-one geotypes and their properties in relation to groundwaters were thus integrated in a GIS and completed with geophysical and boreholes data. The achievement of the new groundwater protection areas maps is currently in the pipeline for the whole canton of Vaud, while the implementation of the new methodology forgeothermal heat pump admissibility mapping (riquiring the building of a 3D geological model) is still being tested

Using predisposition factors for landslide hazard assessment: a new GIS-based methodology

Switzerland is exceptionally subjected to landslides; indeed, about 10% of its area is considered as unstable. Making this observation, its Department of the Environment (BAFU) introduced in 1997 a method to realize landslide hazard map. It is routinely used but, like most of the methods applied in Europe to map unstable areas, it is mainly based on the signs of previous or current phenomena (geomorphologic mapping, archive consultation, etc.) even though instabilities can appear where there is nothing to show that they existed earlier. Furthermore, the transcription from the geomorphologic map to the hazard map can vary according to the geologist or the geographer who realizes it: this method is affected by a certain lack of transparency and is not really efficient to forecast landslides. The aim of this project is to introduce the bedrock of a new method for landslide hazard mapping; based on instability predisposition assessment, it involves the designation of main factors for landslide susceptibility, their integration in a GIS to calculate a landslide predisposition index and the implementation of new methods to evaluate these factors; to be competitive, these process will have to be both cheap and quick. After showing that cohesion and hydraulic conductivity of loose materials were strongly linked to their granulometry and plasticity index, we implemented two new field tests, one based on teledetection and one coupled sedimentometric and blue methylen tests to evaluate these parameters. The hydraulic conductivity of fractured rocks was obtained from the analysis of their geometrical properties (fractures density, aperture size and orientation). The other factors were extracted from DEM and hydrologic mapping. We added a last factor related to the predisposition of the geotype (new classification for geologic formations, based on genetic standards for loose material and on lithologic standards for hard rock) to slope instability process: the latter enabled us to integrate attributes proper to each geotypes (over-consolidation for ground moraines, stratifications for glaciolacustrine deposits, etc...) and which would be long and complex to integrate to a GIS. Afterward, we implemented an ArcGis® toolbox allowing to lead to a landslide susceptibility index. Finally, we applied this methodology (from field survey to GIS operations) to ten sites in different contexts in Switzerland. This new methodology can be considered as a cheap and efficient way to forecast landslides

GIS-based 3D modelling for landslide hazard assessment: increasing the objectivity of hazard maps.

Recent decades have been marked by many disasters caused by natural hazards.Gravitational phenomena in particular have resulted in several deaths and extensive damage to infrastructure. Nearly 10% of Swiss territory is considered unstable. It therefore requires an effective methodology for the mapping of areas likely to be affected by this type of hazard. The aim of this project is to establish the bedrock of a new methodology for the implementation of hazard maps related to landslides based on the evaluation of slope instability predisposition. The first step of this methodology is a systematic field survey on a given study area. The information is organized by type (faults, dip, formations, boreholes, springs, streams, etc..) and then imported into a GIS. Once these data interpolated and converted into a grid of points, we obtain on the one hand a three-dimensional geological model (supplemented by geotechnical and hydrodynamic parameters measured in situ and extrapolated to the entire study area) and on the other hand an approximation of the gradient of hydraulic potential in the area.It is then possible to calculate a safety factor at each point of the model and thus to assess the susceptibility of the slope to instabilities. After crossing with a map of moderating factors (altitude, aspect, vegetation) in order to take into account the context of the slopes, it is validated by comparison with the map of phenomena to obtain the final hazard map. Achieving it is thus entirely transparent

Utilisation des SIG pour la gestion et la protection des ressources en eaux souterraines du canton de Vaud

Devant l’augmentation des conflits entre la préservation des eaux souterraines et l’utilisation des autres ressources du sous-sol, le développement de nouvelles méthodologies d’évaluation et de gestion de ces ressources devient inévitable. Ces méthodes devant être aussi transparentes que possibles, nous avons mis en place des traitements automatisés sur SIG pour la gestion des ressources en aux souterraines ainsi que géothermiques. La première étape de ce projet consistait à réviser les cartes des secteurs de protection des eaux souterraines du canton de Vaud, l’attribution des secteurs se faisant par croisement de l’information géologique de surface, du relief, des sources et de données de géophysique. Cette phase nous a permis de mettre en évidence la principale lacune de cette méthodologie, à savoir les erreurs dues à une mauvaise prise en compte des données en profondeur. Une deuxième étape concerne l’évaluation de l’admissibilité vis-à-vis de l’implantation des sondes géothermiques. Afin de nous affranchir des incertitudes liées au sous-sol, nous avons tout d’abord réalisé un modèle géologique tridimensionnel à partir des données de forage du cadastre géologique. Une fois ce modèle importé dans un SIG sous forme d’une grille de points, on attribue à chaque formation des propriétés vis-à-vis de sa perméabilité. On peut alors mettre en évidence les zones potentiellement aquifères et donc identifier les zones de conflits entre eaux souterraines et forages géothermiques