Vincent Marc

A better understanding of headwater hydrogeology in the semiarid Andes is critical because high‐elevation basins are considered water towers for the main valleys, where water demand is over‐allocated. While the body of literature generally focuses on the contribution of glaciers to streamflow, there is little information on the contribution of sparsely glacierized basins and the origins and processes of groundwater generation at high elevations. The Corrales catchment in North‐Central Chile contains both heavily and sparsely glacierized sub‐basins as well as the highest public borehole in the region, making it suitable to fill such scientific gaps. Geophysical surveys and a pumping test were carried out to obtain information on groundwater flows beneath the Tapado terminal rock glacier and a main tributary of the Elqui River. Radioactive and stable isotopes were used to characterise the hydrological connectivity and the origins of water in the headwater basins. Low electromagnetic velocities and resistivities indicate the presence of liquid water beneath the rock glacier, suggesting the upper limit of a proglacial aquifer. The downstream valley aquifer appears transmissive and dominated by old waters (several decades) that are a mix of high‐glacierized and sparsely glacierized basins. In addition, stable isotopes reveal distinct signatures for high‐glacierized and sparsely glacierized basins, which may be attributed to isotope fractionation. These results suggest that water isotopes can be used to distinguish between waters originating from high‐glacierized and sparsely glacierized basins. The study also identifies the presence of old waters in the sparsely glacierized basins, which indicates long‐term storage, slow release or slow turnover times. This finding is crucial for understanding the evolution of late‐season baseflow and streamflow in the context of climate change. As the contribution of such basins to total streamflow is significant, a better understanding of hydrological processes in sparsely glacierized regions is required.

A better understanding of headwater hydrogeology in the semi-arid Andes is critical because high-elevation basins are considered water towers for the main valleys, where there is over-allocated water demand. While international literature generally focuses on the glacier contribution to streamflow, there is little information on the contribution of sparsely glacierized basins and the origins and processes of groundwater generation at high elevations. The Corrales catchment in North-Central Chile contains both glacierized and s parsely sub-basins as well as the highest public borehole in the region, making it suitable to fill such scientific gaps. Geophysical surveys and a pumping test were carried out to obtain information on groundwater flows beneath the Tapado terminal rock glacier and a main tributary of the Elqui river. Radioactive and stable isotopes were used to characterize the hydrological connectivity and the water origins of the headwater basins. Low electromagnetic velocities and resistivities reveal the presence of liquid water beneath the rock glacier, which could be the upper limit of a proglacial aquifer. The downstream valley aquifer appears transmissive and dominated by old waters (several decades) that are a mix of high-glacierized and low-glacierized basins. Additionally, stable isotopes indicate different signatures for high- and low-glacierized basins, which could result from isotope fractionation. These results indicate that water isotopes could be used to discriminate waters originating from high-glacierized and low-glacierized basins. The study identifies also the presence of old waters in the low-glacierized basins, which indicates long term storage, slow release or low turnover times. This finding is important for understanding late season baseflow and streamflow evolution in the context of climate change. As the contribution of such basins to total streamflow is significant, a better understanding of hydrological processes in sparsely glacierized regions is required.

This study investigates the hydrological processes driving groundwater recharge in the Avignon Plain (south‐eastern France) through a detailed analysis of the interactions between irrigation, rainfall and soil water using long‐term isotopic monitoring and lumped parameter modelling. More than 15 years of monthly isotopic data from rainwater, surface water, soil water and groundwater were analysed to quantify the contributions of gravity‐fed irrigation and natural rainfall to aquifer recharge. Our results show that gravity‐fed irrigation contributes about 85% of the recharge, highlighting the significant role of traditional agricultural practices in maintaining groundwater levels. Through isotopic tracing and modelling, we observed variations in transit times, with faster infiltration pathways associated with irrigation flows compared to more prolonged recharge from rainfall. This study not only demonstrates the effectiveness of isotopic techniques for assessing water sources in complex recharge scenarios but also provides insights into how irrigation practices affect groundwater sustainability. These results contribute to current thinking on sustainable water management and highlight the need for integrated approaches that reconcile agricultural water use efficiency and groundwater conservation.

A better understanding of headwater hydrogeology in the semi-arid Andes is critical because high-elevation basins are considered water towers for the main valleys, where water demand is the highest. Geophysical surveys and a pumping test were carried out to obtain information on aquifer structures and properties. Radioactive and stable isotopes were used to characterize the hydrological functioning of the headwater basins. Low electromagnetic velocities and resistivities reveal the presence of liquid water beneath a rock glacier, which could be the upper limit of a proglacial aquifer. The downstream valley aquifer appears fairly transmissive (3.2 10 ^-3 m ² s ^-1 ) and dominated by old waters (several decades) that are a mix of high-glacierized and low-glacierized basins. Additionally, stable isotopes point out a different signature for high-glacierized and low-glacierized basins, which could result from isotope fractionation. These results indicate that water isotopes could be used to discriminate waters originating from high-glacierized and low-glacierized basins. The study identifies the presence of old waters in a priori low-glacierized basins, which indicates long term storage. This finding is important for understanding late season baseflow and streamflow evolution in the context of climate change. As the contribution of such basins to total streamflow is significant, studies that aim to predict streamflow should not only focus on basins containing large glaciers.

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.

Understanding water infiltration and transfer in soft‐clay shales slopes is an important scientific issue, especially for landsliding. Geochemical investigations are carried out at the Super‐Sauze and Draix‐Laval landslides, both developed in the Callovo‐Oxfordian black marls, with the objective to define the origin of the groundwater. In situ investigations, soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems. At Super‐Sauze, the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations, or at the landslide basement through a fault network. Such external origin of water is not observed at the local scale of the Draix‐Laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows. Hydrogeological conceptual models are proposed emphasizing the role of the interactions between local (slope) and regional (catchment) flow systems. The observations suggest that this situation is a common case in the Alpine area. Expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales.

In many geological contexts, the hydrogeological features of highly fractured rock slabs can drive slope instability processes. This is the case of San Leo (northern Apennines of Italy), where groundwater processes were recognized as predisposing factor for the last large-scale rock fall that took place the 27th of February 2014. In the present work, the hydrogeological features of the San Leo slab were analyzed by means of spring-discharge analysis, piezometric monitoring data and slug tests. The maximum spring yield, the depletion coefficient and the hydraulic conductivity values were estimated. Time-series analyses were used to better understand the groundwater behavior within the rock slab and to estimate its response to rainfall regime. Moreover, the calculation of the groundwater flow direction and modulus in the unsaturated zone was performed. Results highlight the presence of two systems, which are probably related to the characteristics of different joint sets (aperture, spacing); the hydraulic conductivity values were shown to vary with depth. A first general interpretation of the aquifer behavior is given, which is related to the main structural elements of the slab

Rainfall is one of the major triggering factors of landslides, and its pattern controls their temporal behaviour. Characterization of the groundwater processes and possible preferential infiltration of rainfall is necessary, challenging and very relevant for landslide hazard analysis. The objective of this paper is to identify the groundwater dynamics (matrix flow and preferential flow) within highly heterogeneous and fissured reworked black marl material, using a large‐scale infiltration test. The artificial rainfall experiment over a 100 m² infiltration plot monitored with several hydrological, hydrochemical and geophysical equipments was carried out on the Super‐Sauze mudslide (South French Alps). High resolution groundwater and water quality measurements were collected. Artificial rainfall was applied over a period of 14 days. Conservative tracers (Br⁻ and Cl⁻) were used successively during the infiltration period. The mean rainfall intensity was 8·5 mm h⁻¹ with a mean tracer concentration of 100 mg l⁻¹. The hydrodynamic and hydrochemical responses of the tracing experiments allowed us to get a new insight into: (1) the horizontal and vertical variability of the rain infiltration in unstable black marl hillslopes; (2) the effect of shallow fissuration on the groundwater recharge; (3) the role of piston flow on the rate of water level changes and the increase of pore water pressures and (4) the effect of material heterogeneity in the development of preferential water flows and local perched water tables. Copyright © 2011 John Wiley & Sons, Ltd.

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.