The karst aquifers of India are an indispensable source of water to millions of people but the current globalization and climate change have altered the hydrological and other processes and thus have threatened the sustainability of the groundwater reserves in both quantity and quality. The study aims to conceptualize the recharge processes and estimate the groundwater recharge in a karst aquifer located in semi-arid southern India. For this reason, we used stable isotopes of rain and groundwater to understand aquifer dynamics and estimate the recharge volume as well as gain knowledge about different factors that are affecting the aquifers. The isotope data show that the southwest-monsoon rainwater has a weighted mean (WM) delta H-2, delta O-18, and chloride concentration of -10.5 parts per thousand, -1.03 parts per thousand, and 0.81 mg/L, respectively. The rainfall of other seasons is highly depleted in heavy isotopes. The delta H-2 vs. delta O-18 plots of rainwater and groundwater suggest that recharge is highly variable in space and time and depends on climatic factors as well. A mixing model based on isotopes and chloride values shows that recharge around highly karstified areas of the aquifer is about 64% and largely infiltrates as fast allogenic type. High hydraulic conductivity and fast transfer velocity make such areas very prone to contamination. Irrigation return-flow contributes about 53% of the aquifer storage in the paddy cultivated areas, which along with several other factors contaminate the groundwater. This study provides an estimated annual replenishable groundwater volume of the Narji Limestone aquifer of 1031 +/- 180 MCM. The chemical and isotope modeling enables a better understanding of water resources in fractured karst aquifer and the study encourages their use to investigate the karst hydrodynamics in India and elsewhere as well.

Le Brgm et le Cerema collaborent pour proposer pour la premiere fois une methode d'evaluation de l'alea mouvements de terrain lie au karst. Un guide technique exposera d'ici 2021 les specificites des contextes karstiques et la demarche proposee (analyse multicritere). Les cartographies predictives pouvant ainsi etre obtenues seront utiles aux reflexions locales d'urbanisme.

Core Ideas Long‐term observatories allow the study of global changes to water resources in India. Crystalline rock aquifers are highly heterogeneous. Management of crystalline aquifers necessitates solving several scientific questions. A multidisciplinary approach is necessary for improving water management in India. Multiscale and long‐term work is needed to tackle the scientific challenges found in areas vulnerable to climate change and anthropic pressure. This is the case in the semiarid and drought‐prone regions of southern India where freshwater is scarce and agriculture near fast‐growing cities is triggering high water demand. The Indo‐French Center for Groundwater Research (IFCGR) was established in 1999 between the Indian National Geophysical Research Institute (NGRI) and the French Geological Survey (BRGM) at the NGRI campus in Hyderabad, India. For almost 20 yr, the IFCGR has studied the hydrodynamic properties and associated hydrological processes in crystalline aquifers. To that end, the Center set up two sites for observing groundwater in crystalline rock aquifers: (i) the Maheshwaram basin for the study of groundwater management at catchment scale, and (ii) the Choutuppal experimental site for the detailed study of hydrogeological processes at local scale (between wells). Multiscale approaches allow the characterization of hydrodynamic and transport properties of the shallow weathered part of such crystalline aquifers and the implications for groundwater management under overexploitation conditions. The objective is to provide suitable characterization of aquifer properties for developing modeling and management tools applicable to such heterogeneous aquifers.

The Loire River basin is regularly impacted by sinkholes because of its specific geological context, karstic limestone overlain by soft cover deposits. The intense rainfall event and the associated floods that occurred in this area in May and June 2016 triggered tens of sinkholes in a few square kilometers. At least 20 houses, one flood protection dyke of the Loire River and two highways were damaged by collapses. These events highlight not only the vulnerability of the area, especially in the case of a disastrous flood of the Loire River, but also the unexpected kinetics of the collapse process. Two different types of sinkholes occurred in the impacted areas: north of Orléans, collapses of the filling of vertical caves are suspected; in the Loire valley, the flood accelerated the internal erosion of alluvium in the karstic active network, triggering cover collapses (spatial and temporal sinkhole frequency increased by an estimated factor of 16,000 to 24,000). In parallel, an innovative internal erosion numerical modeling approach, based on Discrete Element - DEM and Lattice Boltzmann methods - LBM, has been developed through a partnership between the French Geological Survey (BRGM) and the Environment and Agriculture National Research Institute (IRSTEA). The upward propagation of cavities within the cover were successfully simulated. The role of different parameters (soft cover cohesion, hydraulic head, system geometry, etc.) in the sinkhole occurrence were tested by a parametric analysis.

Core Ideas SNO KARST is dedicated to the study of karst functioning. Hydrodynamics and geochemistry are measured at springs and in karst compartments. Process sampling was set up at nine sites in various climatic contexts. Continuous monitoring concerns timescales from 10 to >50 yr. New tools and findings are due to the complementarity of gathered data. Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface–groundwater interactions. Improving the understanding of karst functioning is thus a major issue for the efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems across a wide range of spatiotemporal scales under different geological, geomorphological, climatic, and soil cover settings. The objective of the French Karst National Observatory Service (SNO KARST) is to supply the international scientific community with appropriate data and tools, with the ambition of (i) facilitating the collection of long‐term observations of hydrogeochemical variables in karst, and (ii) promoting knowledge sharing and developing cross‐disciplinary research on karst. This paper provides an overview of the monitoring sites and collective achievements, such as the KarstMod modular modeling platform and the PaPRIKa toolbox, of SNO KARST. It also presents the research questions addressed within the framework of this network, along with major research results regarding (i) the hydrological response of karst to climate and anthropogenic changes, (ii) the influence of karst on geochemical balance of watersheds in the critical zone, and (iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds.

Western Himalaya is a strategically important region, where the water resources are shared by China, India and Pakistan. The economy of the region is largely dependent on the water resources delivered by snow and glacier melt. The presented study used stable isotopes of water to further understand the basin-scale hydro-meteorological, hydrological and recharge processes in three high-altitude mountainous basins of the western Himalayas. The study provided new insights in understanding the dominant factors affecting the isotopic composition of the precipitation, snowpack, glacier melt, streams and springs. It was observed that elevation-dependent post-depositional processes and snowpack evolution resulted in the higher isotopic altitude gradient in snowpacks. The similar temporal trends of isotopic signals in rivers and karst springs reflect the rapid flow transfer due to karstification of the carbonate aquifers. The attenuation of the extreme isotopic input signal in karst springs appears to be due to the mixing of source waters with the underground karst reservoirs. Basin-wise, the input–output response demonstrates the vital role of winter precipitation in maintaining the perennial flow in streams and karst springs in the region. Isotopic data were also used to estimate the mean recharge altitude of the springs.

Recharge assessment is a challenge in snow and glacier dominated Himalayan basins. Quantification of recharge to karst springs in these complex geological environments is important both for hydrologic understanding and for effective water resource management. We used spring hydrographs and environmental tracers (isotopes and solutes) to distinguish and estimate the sources of spring water and to identify the flow paths of the recharging waters in three mountainous basins of the western Himalaya. The karst springs are perennial with high discharge amplitudes. The results indicate that ambient temperature has a strong influence on the hydrological behavior of the springs. Although the spring flow is dominantly controlled by the melting of snow and/or glaciers, rain events produce sharp spikes in spring hydrographs. The fades patterns in springs within the Bringi basin (Ca-HCO3) and the Liddar basin (Ca-HCO3 and Ca-Mg-HCO3) suggest flow dominantly through limestone and dolomite. Higher concentrations of SO42- and Na+ in warm springs of the Kuthar basin indicate flow through carbonate, silicate and other rocks. The isotopic composition (delta O-18 delta H-2) of precipitation, snowpacks, glacier melt and karst springs show wide variation both in space and time, and are strongly influenced by the basin relief and meteorology. The tracer-based two- and three-component mixing models suggest that the snowmelt dominantly contributes to the spring flow (55-96%), followed by glacier melt (5-36%) and rain (4-34%). Based on tracer tests with good recovery rates, springs are dominantly recharged through point sources rather than by diffuse infiltration. Changes in the timing, form, and amount of winter precipitation substantially affect the timing and magnitude of spring discharge during the rest of the year. (C) 2017 Elsevier B.V. All rights reserved.

As many states in India, Andhra Pradesh is currently facing a general overuse of the groundwater resource mainly due to agriculture irrigation growing demand. Despite water harvesting measures supported on a massive scale by government and non-government watershed development programmes, groundwater levels are declining. New programmes are being implemented to improve artificial percolation whilst the impact of former measures on groundwater recharge is still undefined. The few studies carried out so far estimate percolation fraction of artificial tanks from 35% to 50% in hard-rock aquifer context while downstream runoff is reduced by 12% to 20%. Downstream impact of upstream watershed development becomes a key question for future programmes and has to be answered by separating climate and human impacts. The present study focuses on a detailed water accounting of a typical artificial tank through intensive monitoring. During the period of observation, the total runoff generated within the catchment is stored in the tank and 35% of the stored water disappears by percolation. It appears that heavy siltation may be the main limiting factor for percolation efficacy.

ABSTRACTWe investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling. Standard geometrical geological modelling can be strengthened using geophysical data. Here, we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces. The proposed method is illustrated on an airborne electromagnetic survey conducted in the region of Courtenay in France. First, a resistivity contrast corresponding to the clay/chalk interface was interpreted confronting the electromagnetic soundings to boreholes. Slopes were then sampled on this geophysical model and jointly interpolated with the clay/chalk interface documented in boreholes using an implicit 3D potential‐field method. In order to evaluate this new joint geophysical–geological model, its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations. The proposed joint modelling yields the most accurate clay/chalk interface whatever the number and location of boreholes taken into account for modelling and validation. Compared with standard geological modelling, the approach introduces in between boreholes geometrical information derived from geophysical results. Compared with conventional resistivity interpretation of the geophysical model, it reduces drift effects and honours the boreholes. The method therefore improves what is commonly obtained with geological or geophysical data separately, making it very attractive for robust 3D geological modelling of the subsurface.

Western Himalaya is a strategically important region, where the water resources are shared by China, India and Pakistan. The economy of the region is largely dependent on the water resources delivered by snow and glacier melt. The presented study used stable isotopes of water to further understand the basin-scale hydro-meteorological, hydrological and recharge processes in three high-altitude mountainous basins of the western Himalayas. The study provided new insights in understanding the dominant factors affecting the isotopic composition of the precipitation, snowpack, glacier melt, streams and springs. It was observed that elevation-dependent post-depositional processes and snowpack evolution resulted in the higher isotopic altitude gradient in snowpacks. The similar temporal trends of isotopic signals in rivers and karst springs reflect the rapid flow transfer due to karstification of the carbonate aquifers. The attenuation of the extreme isotopic input signal in karst springs appears to be due to the mixing of source waters with the underground karst reservoirs. Basin-wise, the input–output response demonstrates the vital role of winter precipitation in maintaining the perennial flow in streams and karst springs in the region. Isotopic data were also used to estimate the mean recharge altitude of the springs.

An innovative approach for regionalizing the 3‐D effective porosity field is presented and applied to two large, overexploited, and deeply weathered crystalline aquifers located in southern India. The method derives from earlier work on regionalizing a 2‐D effective porosity field in that part of an aquifer where the water table fluctuates, which is now extended over the entire aquifer using a 3‐D approach. A method based on geological and geophysical surveys has also been developed for mapping the weathering profile layers (saprolite and fractured layers). The method for regionalizing 3‐D effective porosity combines water table fluctuation and groundwater budget techniques at various cell sizes with the use of satellite‐based data (for groundwater abstraction), the structure of the weathering profile, and geostatistical techniques. The approach is presented in detail for the Kudaliar watershed (983 km 2 ) and tested on the 730 km 2 Anantapur watershed. At watershed scale, the effective porosity of the aquifer ranges from 0.5% to 2% in Kudaliar and between 0.3% and 1% in Anantapur, which agrees with earlier works. Results show that (a) depending on the geology and on the structure of the weathering profile, the vertical distribution of effective porosity can be very different and that the fractured layers in crystalline aquifers are not necessarily characterized by a rapid decrease in effective porosity and (b) that the lateral variations in effective porosity can be larger than the vertical ones. These variations suggest that within a same weathering profile, the density of open fractures and/or degree of weathering in the fractured zone may significantly vary from a place to another. The proposed method provides information on the spatial distribution of effective porosity that is of prime interest in terms of flux and contaminant transport in crystalline aquifers. Implications for mapping groundwater storage and scarcity are also discussed, which should help in improving groundwater resource management strategies.

Sinkholes in Val d’Orléans occur regularly and can have significant socio-economic impacts. They are due to the presence of a karstified limestone under 5–15-m-thick alluvial deposits. Intense karstification within the area is caused by infiltration of large amount of Loire River water in the karst aquifer through swallow holes. Two mechanisms for the formation of sinkholes are proposed: (1) suffosion of alluvial deposits towards the karstic conduits leading to the occurrence of a void at the base of the alluvium that will progressively enlarge up to reach the surface; (2) karst conduit ceiling breakdown as a consequence of conduit size evolution and/or hydrostatic pressure changes within the karst aquifer. In order to better understand the mechanisms leading to sinkhole occurrence, an experimental site comprising groundwater and surface deformation monitoring has been set up in an area known to be regularly impacted by new sinkholes. First results show similar groundwater level variations in the alluvial and karstic aquifers with, however, a small difference at the beginning of recession limbs when the alluvial aquifer shows higher water levels compared to the karstic aquifer. This situation may favour suffosion and/or sloughing. The comparison of water chemistry between Loire River and karst groundwater seems to indicate very active dissolution processes directly downgradient of the swallow holes and a potential rapid evolution of karst conduit sizes. Such an evolution can contribute to conduit ceiling breakdown resulting in collapse sinkholes. Obtained results bring new insights that will be useful for adequate sinkhole risk management (e.g. hazard mapping and surveillance methodology, etc.).

Summary Airborne Time Domain ElectroMagnetic (TDEM) and magnetic (MAG) surveys have successfully been used for environmental studies. In igneous provinces, TDEM and MAG data may be jointly interpreted for the characterization of the geological environment. In May 2015, a heliborne survey was conducted in New-Caledonia Island (south-west in the Pacific Ocean) over a small area nearby Koné for hydrogeological characterization. The area is hosted by pre-Late Cretaceous metamorphic unit, Cretaceous formations, two volcanic facies and peridotite massifs, relic of the ophiolite nappe. TDEM and MAG data were separately and jointly interpreted in order to characterize the Koné area. Separately, results obtained from the two methods provided new information on the hydrogeological environment and allow delineating the precise limits of the different geological formations. Jointly, the multilayered results were interpreted using a hierarchical ascendant clustering algorithm. Through a statistical classification of three MAG grids and three TDEM grids, it was possible to propose a predictive geological map for the Koné area. The input will help to better manage the groundwater resources and will be used to position new exploration wells.

Using a recently developed 2D numerical modelling that combines Discrete Element (DEM) and Lattice Boltzmann methods (LBM), we simulate the destabilisation by an hydraulic gradient of a cohesive granular soil clogging the top of an underground conduit. We aim to perform a multi-scale study that relates the grain scale behavior to the macroscopic erosion process. In particular, we study the influence of the flow conditions and the inter-particle contact forces intensity on the erosion kinetic.

Soil subsidence/collapse is a major geohazard occurring in karst regions. It occurs as suffosion or dropout sinkholes developing in the overburden overlying karst. Less frequently it corresponds to a breakdown of karst void ceiling (i.e., collapse sinkhole). This hazard can cause significant engineering challenges. Therefore decision-makers require the elaboration of methodologies for reliable predictions of such hazards (e.g., karst subsidence susceptibility and hazards maps, planning strategies, priority areas for detailed investigations). This study aims at developing a methodological framework for the evaluation of potential conditioning factors controlling the occurrence of sinkholes in a context of limestone karst: potential conditioning factors are first determined based on underlying physical processes for different geological contexts (barren and mantled karsts). Then the relevance of each factor is evaluated against a set of representative karst subsidence locations using the weight-of-evidence theory and relevant factors are tested for independence. Relevant and independent factors are finally weighed and combined together (i.e., superimposed) to achieve karst subsidence susceptibility models. The best model (i.e., the one showing the highest predictability) is determined by a receiver operating characteristic (ROC) curve analysis, which is performed using a set of independent and representative karst subsidence locations.The method is applied to one case study where mantled karst setting prevails (Val d'Orleans, south of Paris). Results show higher susceptibility in mantled karst with significant role of the overburden lithology (presence/absence of low-permeability layer) and position of the karst piezometric surface within the overburden. The limited area of barren karst shows a low susceptibility.Although this approach was developed for a specific karst context, it can easily be replicated in other karst contexts (e.g., interstratal karst, chalk or evaporitic karsts) which are known to be highly susceptible to karst subsidence even if some of the conditioning factors will be different. (C) 2015 Elsevier BM. All rights reserved.

Summary In a traditional HEM inversion scheme, the voltage data are usually normalized by the effective area of the system. This effective area depends on the tilt of the frame; the pitch and the roll of the frame are monitored during the survey with tilt-meters and used to calculate a correction term. However, using the measured tilt to calculate this term, it is assumed that the terrain is flat, which may lead to inaccuracies on the inversion results. Thus, though the correction term is generally small, it can prove important to accurately compute it in rugged terrain when high resolution is needed. The measured tilt has then to be corrected by the apparent slope of the ground in order to determine an effective tilt at each measurement location. In this work we compute the effective tilt and evaluate its contribution on inversion results. This was achieved on a recent survey conducted over La Réunion, which has a very rugged terrain. The inversion results obtained using the effective tilt were compared to the ones obtained with the measured tilt. Using the effective tilt in such environment has a clear effect in the inversion results, both on resistivity patterns and on the DOI.