Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 5 1 2005 10.5194/nhess-5-71-2005 http://www.nat-hazards-earth-syst-sci.net/5/71/2005/ http://www.nat-hazards-earth-syst-sci.net/5/71/2005/nhess-5-71-2005.html http://www.nat-hazards-earth-syst-sci.net/5/71/2005/nhess-5-71-2005.pdf 71 85 2005-01-06 Forecasting the behaviour of complex landslides with a spatially distributed hydrological model J.-P. Malet Th. W. J. van Asch R. van Beek O. Maquaire Faculty of Geosciences, UCEL, P.O. Box 80115, 3508 TC Utrecht, The Netherlands Institute of Global Physics, School and Observatory of Earth Sciences, UMR 7516 ULP-CNRS, 5, rue Descartes, F-67084 Strasbourg Cedex, France Géographie Physique et Environnement, LETG-Geophen, UMR 6554 CNRS, Esplanade de la Paix, BP 5186, F-14032 Caen Cedex, France The relationships between rainfall, hydrology and landslide movement are often difficult to establish. In this context, ground-water flow analyses and dynamic modelling can help to clarify these complex relations, simulate the landslide hydrological behaviour in real or hypothetical situations, and help to forecast future scenarios based on environmental change. The primary objective of this study is to investigate the possibility of including more temporal and spatial information in landslide hydrology forecasting, by using a physically based spatially distributed model. Results of the hydrological and geomorphological investigation of the Super-Sauze earthflow, one of the persistently active landslide occurring in clay-rich material of the French Alps, are presented. Field surveys, continuous monitoring and interpretation of the data have shown that, in such material, the groundwater level fluctuates on a seasonal time scale, with a strong influence of the unsaturated zone. Therefore a coupled unsaturated/saturated model, incorporating Darcian saturated flow, fissure flow and meltwater flow is needed to adequately represent the landslide hydrology. The conceptual model is implemented in a 2.5-D spatially distributed hydrological model. The model is calibrated and validated on a multi-parameters database acquired on the site since 1997. The complex time-dependent and three-dimensional groundwater regime is well described, in both the short- and long-term. The hydrological model is used to forecast the future hydrological behaviour of the earthflow in response to potential environmental changes.