The role of the soil moisture balance in the unsaturated zone on movement and stability of the Beline landslide, France

The aim of this paper is to analyse the role of the unsaturated zone in groundwater recharge in a landslide and the effect of land use change on its stability. This is studied on the basis of the Beline landslide situated near Salins-les-Bains (Jura, France). The unsaturated zone was modelled using the Hydrus-1D model. Model calibration was based on soil moisture time series using an inverse modelling approach. The unsaturated zone model accurately modelled the soil moisture content time series in 1996 and 1997. The groundwater model was capable of modelling both the average groundwater level and the amplitude of the groundwater level fluctuation, but failed to model the dynamics and the precise timing of the fluctuations. The influence of changes in potential evapotranspiration was studied by changing this input parameter by 10 to 20 per cent as both an increase and decrease. The effects of these changes were quite large. Since the hydrological model chain was able to predict peak groundwater levels quite well, these peak levels were used to calculate maximum moving velocities of the landslide for different evapotranspiration scenarios. The simulations show that a decrease in evapotranspiration up to 20 per cent results in a 20-fold increase in maximum velocity. An increase in evapotranspiration (10 to 20 per cent) will probably stabilize the landslide for most of the time. Copyright © 2002 John Wiley & Sons, Ltd.