Investigations of hydric and hydrogeological mechanisms that contribute to the current reactivation of mass-movements feed predictive models that can be useful for risk management. Ours are based on an approach combining 1/ a large scale analysis of the landforms, using LiDAR imagery and field observations, 2/ a characterization of the groundwater (piezometry, conductivity and temperature), both in the landslide and in the stable slope, and 3/ electrical resistivity profiles. These combined data allow the reconstruction of the structure of the landslide to determine its influence on groundwater flow. The Saint Maur landslide bars the main aquifer of the Upper Ypresian sands whose slow flow results in lower piezometric level fluctuations and stronger mineralization than found in the unconfined aquifer on either side of the slip. The confined aquifer emptying occurs through the sliding plane so that the landslide aquifer is fed essentially by capillary rise from the shear plane and to a lesser extent by surface infiltration. Therefore, the amount of water in the landslide and the resulting probability of mass movement are weakly correlated with rainfall events. In addition, the wide dispersion of the conductivity values of the landslide aquifer reflects a weak mixing of the water. Groundwater circulation modelling allows to correct in situ – i.e. underground – the flows causing reactivations, and confirms stabilization by hydro-geological action to be more efficient than a surface drainage.

Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/role-of-water-in-destabilizing-slopes

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