Impact of the storm Alex on water exchanges between the Roya River and its alluvial aquifer

The alluvial aquifer of the transnational Roya River watershed is an important water resource for drinking water supply. Through successive European projects, a monitoring network has been implemented over the alluvial plain to improve the understanding of the functioning of this aquifer. For instance, studies highlighted the predominant role of surface water in the recharge of the aquifer. Following the storm Alex and the resulting exceptional flood event in the Roya valley in October 2020, a general decrease of the piezometric levels was observed in the alluvial aquifer. Changes in the river morphology and in the granulometry of the hyporheic zone have impacted surface water – groundwater exchanges and reduced the aquifer recharge.</p

Socio-economic assessement of farmers' vulnerability as water users subject to global change stressors in the hard rock area of southern India. The SHIVA ANR project

International audienceDemand for vulnerability assessments is growing in policy-making circles, to support the choice of appropriate measures and policies to reduce the vulnerability of water users and resources. Through the SHIVA ANR project, we are seeking a method to assess and map the vulnerability of farmers in southern India to both climate and socioeconomic changes, and secondly, to assess the costs and benefits associated with trends farmers' vulnerability in the medium and long-term. The project is focusing on southern India 's hard rock area, as in the geological context, both surface and ground water resources are naturally limited. We are also focusing on farming populations as these are the main water users in the area and rely exclusively on groundwater. The area covers southern India's semi-arid zone, where the rainfall gradient ranges from 600 mm to 1100 mm. Vulnerability is expected to vary according to local climatic conditions but also the socioeconomic characteristics of farming households. The SHIVA research team has been divided into six thematic groups in order to address the different scientific issues : downscaling the regional climate scenario, farm area projections, vulnerability assessments and quantification, vulnerability mapping, hydrological modelling and upscaling, and vulnerability impact assessements. Our approach is multidisciplinary to cater for for numerous inherent themes, and integrated to cater for vulnerability as a dynamic and multidimensional concept. The project 's first results after 10 months of research are presented below

Application of multi‑method approach to assess groundwater–surface water interactions, for catchment management

Globally, the dependence of river systems to delayed discharge of subsurface water to augment flows during dry seasons is well documented. Discharge of fresh subsurface water can dilute concentrated river flow quality during reduced flow. Observed and reported results on the Berg River’s declining water quantity and quality are a concern to the regions socio-economic growth and environmental integrity. Understanding the role of subsurface water discharges on the quantity and quality of receiving surface water courses can improve their management during dry periods. A case study was designed and implemented in the upper Berg River catchment in the Western Cape Province of South Africa to assess the influence of groundwater–surface water interaction on water quantity and quality. This study aimed to quantify and characterize the quality of subsurface water available in the upper catchment to improve observed declining water quality downstream. Hydrograph separation provided estimates of water fluxes during 2012–2014 low and high flow periods, while hydrochemical analysis provided insights on impacts of major land use activity in this catchment on water resources. Hydrograph separation analysis indicated that the Berg River is 37.9% dependent on subsurface water discharges annually. Dominant Na–Cl-type water indicates the quality of water from the upper Berg River is largely affected by natural processes including short residence times of aquifer water, rock–water interactions and atmospheric deposition of NaCl ions. These results provide insights for suggesting management options to be implemented to protect subsurface water for continued dilution and water resources management in the lower catchments

Dataset on onshore groundwaters and offshore submarine spring of a Mediterranean karst aquifer during flow reversal and saltwater intrusion

This dataset was generated to study the behavior of a Mediterranean coastal (Thau lagoon, southern France) karst aquifer for which the flow reversal phenomenon has occurred several times in the past through a submarine karst spring located at -29.5 meters below the lagoon level. Since the 1960s, seven flow reversal phenomena have occurred, the last one occurring between 11/28/2020 and 03/14/2022. During these phenomena, which can last from a few weeks to several months, the salty water is absorbed from the lagoon to the conduit of the submarine spring, which leads to the salinization of the underlying karst aquifer. The equipment and the monitoring of the submarine spring constitute a key element of the research project to understand of the hydrogeological functioning of the karst system during regular conditions, when fresh groundwater flows out of the submarine spring, as well as during disruptive events, when flow reversal and salty water intrusion through the spring occur. The submarine spring flow dataset is contained in the Vise_Submarine_Spring.xlsx file, which contains three excel sheets. The first sheet named &quot;Flow&quot; contains the data of the hourly averages of the flow rates measured at a time step of 5 minutes between 06/26/2019 and 12/31/2022. During regular flowing conditions (i.e. groundwater flows out of the spring), the flow rate is positive. During flow reversal periods, the flow rate becomes negative. The &quot;Comments&quot; column is used to qualify this flow context. The second sheet named &quot;SpC&quot; and the third sheet named &quot;Temp&quot; contain, data of the hourly averages of water specific conductivity and temperature data, respectively, measured at a 5 minutes time step between 06/26/2019 and 10/13/2022. During flow reversal periods, the specific conductivity and temperature measured are those of the lagoon water, these measurements make it possible to qualify the physico-chemical properties of the salty water infiltrated by the karst spring during disruptive events.The lagoon water level dataset is contained in the Thau_Lagoon.xlsx file. The sheet named “WaterLevel” contains the hourly data of the lagoon water levels measured at the H-lagoon site. The data is expressed in meters above sea level. Measured lagoon water level fluctuations were repeatedly checked at the reference point using a manual water level gauge. The groundwater dataset is contained in the Thau_karst_groundwater.xlsx file, which has 9 sheets, one for each of the following stations referenced to the BRGM groundwater database (BSS number with hypertext links). Each sheet contains piezometric data (expressed in m.a.s.l) between 01/01/2017 and 12/31/2022 for the longest time series. The sheets also provides the groundwater temperature and specific conductivity data (with the exception of point BSS002JEKD). Information on the depth of the measurement probe is indicated into the metadata section of each excel sheet.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Characterizing a coastal karst aquifer using an inverse modeling approach: The saline springs of Thau, southern France

A methodological approach using inverse modeling was used to characterize the functioning of the deep and shallow reservoirs of the Thau karst aquifer system. Three springs were monitored at the convergence of rising saline water diluted with shallow groundwater in karst conduits and unmixed shallow groundwater that behaves as confined groundwater. In such a method, impulse responses of flow and fluxes are combined in order to separate hydrographs. The model explains the salinity and hydraulic head variations of the submarine and inland springs. It confirms and improves the conceptual model of this groundwater system in which mixing of saline and subsurface waters occurs. The different forces driving the upward flowing mixed water into the drainage axis and faults were studied in order to elucidate the springs\u27 functioning. A comparative study of spring functioning is proposed, which clearly shows the very high sensitivity of the groundwater system to changes in recharge and discharge conditions

Water storage and transfer in the epikarst of karstic systems during high flow periods

A monitoring of spring and rain waters in the South of France during two hydrological cycles is presented. Rain waters were sampled after each precipitation event at 3 rain-gauge stations. Four karstic springs located in the same area have also been daily (high discharge events) to monthly (low flow periods) sampled. This paper focuses on compositional changes in the Cl− and Br− ions and the oxygen-18 (δ18O) and hydrogen (δD) isotopes during the high discharge events. The responses of the different karstic systems are quite homogeneous and reflect the hydrological state of the system. The waters discharged during the major autumn and winter high discharge events originate from the epikarstic reservoir and show characteristics chemical variations related to residence in the unsaturated zone close to the surface. Their residence time in the order of 1–3 months. Correlations between the composition of the spring-water and the rainwater during three successive high discharge events during the summer of 1998 indicate that the water for high discharge event “n” is derived from water from precipitation event “n − 1” via a piston-type mechanism with residence time of 2 weeks. These results are interpreted as an indication of the major role of the epikarst reservoir in the karst recharge functioning. The similar behaviour of the four springs, although located in different geological contexts allows to think that the epikarst role could be more important than previously thought

De la caractérisation géologique et de la mise en place de la karstification en contexte méditerranéen à l’étude hydrogéologique. Quel transfert possible pour l’étude des aquifères karstiques de la craie ?

La compréhension du développement de la karstification constitue une étape essentielle dans l’étude des régions karstiques en vue de l’évaluation et de la gestion de la ressource en eau souterraine des aquifères karstiques. L’élaboration des systèmes karstiques du pourtour méditerranéen a été fortement influencée par les variations du niveau de base, liées d’une part aux fluctuations du niveau marin et d’autre part aux mouvements tectoniques. Une méthodologie d’étude a été développée et testée sur un système karstique dans les Corbières Orientales (système du Bas-Agly). Cette méthodologie consiste à replacer le massif karstique dans un contexte de géodynamique de bassin sédimentaire. L’étude consiste (i) à effectuer une synthèse des périodes propices au développement de la karstification en considérant conjointement la géodynamique régionale et la charte eustatique mondiale et (ii) à reconnaître les morphologies d’aplanissement et l’enregistrement sédimentaire fossile des massifs karstiques. D’autre part, l’étude du fonctionnement hydrogéologique du système basée sur une approche globale à l’aide de décomposition d’hydrogrammes permet d’aboutir à un modèle conceptuel. Les interprétations hydrogéologiques sont cohérentes et mieux contraintes par les indicateurs géologiques. La mise en place de la karstification des aquifères de la Craie a été abordée jusqu’à ce jour par l’étude des réseaux de fracturation, par l’analyse morphologique spatialisée ou encore par l’étude sédimentologique des dépôts endo et exokarstiques. De nombreuses publications concernant l’évolution paléogéographique de la Craie existent par ailleurs. L’ensemble de ce matériel pourrait permettre un transfert de méthodologie et ouvrir peut être de nouvelles perspectives sur l’étude des systèmes aquifères de la Craie