The Super‐Sauze mudslide is a persistently active slow‐moving landslide occurring in the black marl outcrops of the French South Alps. It has been intensively studied since the early 1990s. Geotechnical, geomorphological, geophysical and hydrological investigations have led to a better understanding of the processes governing the landslide motion. Water flows inside the system have been proven to have a major impact. To look closer at the processes involved and especially to gain a better idea of the origin and pathways of the waters, a hydrochemical study was carried out from May 2003 to May 2004. The groundwater was sampled during five field campaigns spread uniformly over the year. Groundwater from a network of boreholes was collected as well as spring waters from the fractured bedrock (in situ black marl) and from the moraine aquifer above the landslide. Results showed that the groundwater chemistry could not be fully explained by rainfall recharge or simple water–matrix equilibrium. A contribution of saline waters coming from the bottom of a thrust sheet overhanging the landslide was required to get the observed high mineralization. On a flow line, the hydrochemical evolution was related to both soil–matrix equilibrium and deep water sources coming up to the surface by means of major faults, the bedding planes and the schistosity. Hydrochemical anomalies made it possible to point out such contributions locally. It was shown that water chemistry and landslide activity were closely related. This hydrochemical investigation also enabled us to better define the hydrosystem limits.Copyright © 2006 John Wiley & Sons, Ltd.

The Barthelasse alluvial aquifer is used to supply water to 180,000 inhabitants. The pumping field is located less than 200 m from the Rhône and is 100% fed by water from the Rhône, which makes it particularly vulnerable to any pollution from the Rhône. Between the Rhône and the pumping field is a Girardon unit, an arrangement that can be found regularly along the banks of the lower and middle reaches of the Rhône, and whose role is to stabilise the banks (alluvial deposits) and to facilitate river navigation. In order to know the transfer times between the Rhône and the pumping field, fortnightly monitoring was carried out over a hydrological year, as well as hourly monitoring during a flood in the winter of 2019. The Rhône shows a cyclicality in its isotopic signature with enrichment in heavy isotopes during the winter period, particularly during floods, and a depletion during the summer period. This variation is found well within the associated alluvial aquifer. The application of LPMs models showed that the average transfer time between the Rhône and the Girardon unit was 20 days and 50 days between the Rhône and the Barthelasse pumping. This study highlighted the importance of using several sampling frequencies to consider the diversity of hydrological situations. For the Rhône, event-based monitoring (flooding) proved to be relevant to account for isotopic variability throughout the year. This work also highlighted the impact of the disruption of hydraulic exchanges between the river and the water table caused by the presence of the Girardon unit in terms of the propagation of contaminants.