Biotechnologie, Agronomie, Société et Environnement (Jan 1999)
The use of the soil map of Belgium in the assessment of landslide risk
Abstract
The analysis is based on a report from the Laboratory of Geomorphology and Remote sensing of the University of Liege concerning Mont-de-l'Enclus hill (Province of Hainaut, 20 kilometers north of the city of Tournai). After a landslide in a street of the hill, the regional administration ordered, in 1998, a detailed study of the hillside (7 square kilometres). The report is in three parts. The first one analyses the influence of human settlement on the landslide hazards. The second one studies all the environmental components in relation to the landslides. Finally, a synthesis map gathers the most important conclusions drawn from the first two parts. The Belgian soil map is very useful when combined with geological and geomorphological data. This is called geo-morpho-pedologic approach. Analysis and comparison have been made with the geographical information system Arc/Info-Arcview. The landslide of the ""rue du Renard"" is located at the interface between discontinuous layers of clay (5 to 15 meters) and sand. Geology gives us a global evaluation of the layer of clay responsible for the landslide. Geomorphology increases the accuracy of location for the clay layer through several elements of the landscape such as superficial landslides, water seepage, concavities and convexities. Pedology matches up previous information through different kinds of data such as texture, ""natural soil drainage"", soil profile and derived series. The geo-morpho-pedological approach is not always effective in foreseeing a landslide phenomenon such as in the case studied. The report from the Laboratoire de Geomorphologie et Teledetection (remote sensing) indicates, however, that the methodology gave better results than the geotechnical approach in this particular case, and it was also less expensive. The geotechnical approach had either not worked, or was too difficult to use because of the geological conditions (lateral variation of clay fades, absence of outcrops).
