EuroKarst 2016, Neuchâtel

Emerging gradually from the sediment and soil, the remarkable stone forests are a rich source of knowledge about the formation of karst surfaces. This is revealed by the details in the rock relief, subsoil rounded forms dominating the lower parts of the stone pillars, and sharp-edged rillen or fluting created by rainwater dominating the peaks. In between, all of the stages of gradual morphological transformation can be clearly seen. The shilin (Shilin County, Yunnan) pinnacles are developed on Permian limestones displaying a wide variety in lithology which, together with differing location (e.g., hillcrest v valley floor), creates their different characteristic shapes. The bedrock in the Shui Jing Po stone pillars is a micrite to microsparite limestone with (in some places) numerous recrystallised bioclasts, peloids, and intraclasts, that is very pure (high calcium carbonate content). The carbonate rock is uniform throughout the researched block of rock. Dolomitized areas, which are a very frequent and important characteristic of a majority of the neighboring stone forests, were not detected in the Shui Jing Po stone forest (Figs. 1.1, 1.2 and 1.3). Lithomorphogenesis, rock and relief of stone pillars, shows typical characteristics of quick development of stone forest from subsoil karren on the top of cones and ridges between them and slower on the slopes beneath.

The availability of high-resolution digital elevation models (DEM) has increased the possibilities of geomorphometric analysis of karst terrains. Apart from the classical terrain parameters (distribution of elevations, slopes, orientations, curvature, etc.), there have been developments of new algorithms that expand further the possibilities of numerical terrain analysis. We present the analysis of the three main features of the karst landscape: the topographic surface, karst hills and karst depressions. Karst depressions and karst hills have been identified and delineated using the DEM and field work. We have developed a system of spatial kernel functions that allows to analyze both the relief and karst depressions and hills. The results will be compared with the main conditioning factors in the development of a karst landscape: geology (lithology and structure) and the system of discontinuities and fractures (faults, joints, etc.). We apply the methodology to the Sierra de las Nieves karst massif, and we conclude how a strong structural control has modeled the landscape.

Sinkholes, of both natural and anthropogenic origins, represent the main geological hazard in Apulia, a region in southern Italy characterized for most of its extension by soluble rocks, with widespread presence of karst caves and man-made cavities. Occurrence of sinkholes in Apulia is described and analysed in this paper, by using the data extracted from the chronological database of sinkholes, produced by CNR-IRPI for the whole Italian territory. It appears that the frequency of documented events strongly increased in the last decades in Apulia, in the aftermath of a series of sinkholes that hit different parts of the region.

The presented case study is part of a series of international research cooperations started in 2006 and still ongoing. The study area is located at the east coast of the Yucatan Peninsula, México, south of the city of Tulum including the northernmost part of the Sian Ka’an Biosphere Reserve. This study focuses on the third aero-electromagnetic (AEM) survey in the area conducted in January 2015 by the Geological Survey of Austria and Amigos de Sian Ka’an and on results prepared in course the Swiss–Mexican–Austrian project ‘Xibalba’. AEM enables quick measurement of the distribution of electrical conductivity in the subsurface over difficult accessible terrain. By means of a common frequency-domain four-channel helicopter probe and application of newly developed data processing algorithms, signatures of karst conduits and aquifers could be resolved. It is shown that the methods are able to deliver crucial structural information about karst groundwater regimes with unique depth information compared to previous surveys.

The Rospo Mare field is a paleokarstic oil field typical of the Mediterranean realm. It has known a complex polyphased evolution that has left a strong diagenetic imprint on the actual paleokarst. The multiscale (seismic, well logs and core) sedimentologic, diagenetic and structural study of the karst features and their infillings has led to the reconstruction of this complex history and has enabled the recognition of key factors controlling reservoir properties. This study, integrated with previous published works, has defined a conceptual framework that has allowed field scale and local adjustments of key reservoir properties, both vertically and horizontally. Good flow simulation results in terms of history matching, and production forecast was thus achieved.

The construction of the combined ship lock weir in Hessigheim, Germany, created a river stage difference of more than 6 m and intensified subsequently the surface–subsurface water exchange and modified the natural subsurface flow field. In the sulfate-bearing hydrogeological setting, increased infiltration and intensified subsurface flow triggered related dissolution processes. Soon after construction, the structure started suffering from subsidence due to progressive leaching and demanded extensive grouting. In the course of approximately 25 years, groundwater heads and subsurface sulfate concentrations responded distinctively to grouting campaigns. The analysis confirms that as a result of its high solubility and altered hydrogeological conditions, gypsum karst develops on a human rather than on a geological time scale. Grouting measures considerably slowed down these processes, however, at the cost of subsurface flow field variations which will ultimately transfer the zone of enhanced dissolution.

The manuscript is devoted to the influence of sulphate karst on engineering structures and the environment. Karst processes are intensified under anthropogenic impact; this fact needs to be considered in the design, construction and operation of various constructions or technical sites. Impact of sulphate karst was studied by the example of the Kama hydroelectric power station, at the base of which gypsum rocks lie, and also in the area of the Polazna oil field.

This paper presents the preliminary results of geomorphological and geological investigations carried out along the valley of the Degano River with a special emphasis on sinkholes. The study area is located in the Degano Valley, Carnian Alps, which are situated in the NE part of Italy. The main village is Ovaro and is historically affected by geohazard associated with ground-subsidence phenomena caused by evaporites, which are widely present in the valley. Traditional investigations have been carried out, and the collection and analysis of historical documents and reports were integrated by aerial photograph interpretation and field surveys. The paper outlines the research phases and the preliminary results achieved which proved fruitful thanks to the application of an integrated approach in the study of sinkhole. Particular attention was paid to the recognition and classification of the phenomena as well as the identification of the buildings damaged by ground subsidence.

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.).

The main focus of the study was to help in the application of the gravity-driven regional groundwater flow (GDRGF) concept for the evaluation of groundwater flow circulation in unconfined and confined sub-basins of carbonates. The concerns of the applicability of GDRGF could be released with focusing not on an individual aquifer but on a carbonate basin and interpret its heterogeneities based on the principle of hydraulic continuity. The approach and the application were demonstrated on the example of the Buda Thermal Karst (BTK), Transdanubian Range (TR), Hungary. The hydraulic connectivity of the system was proved based on the experiences of a long-term “pumping test” for the NE part of the TR. The intense connectivity of thick carbonates could be explained by the higher hydraulic diffusivity compared to siliciclastic regions. The original (before intense water production) spring data of the BTK were grouped based on the results of statistical analysis, and their critical parameters (chloride content, temperature and volume discharge) were displayed in the function of the discharge elevation and grouping of springs. In addition, a 2D flow and heat transport simulation were carried out by EPM approach based on topographic, hydrostratigraphic and structural settings of the BTK (Southern system). Based on the results, the location and chemical and temperature character of one-component thermal springs of the Southern system of BTK could be explained. The thermal springs receive water from regional flow system with additional basinal fluid contribution from the confining Paleogene and Neogene siliciclastic sediments of Pest side. In addition, heat accumulation under the Pest side of BTK also could be revealed. This approach can be used for the understanding of GDRGF of carbonate regions on all over the world.

The Sierra de las Nieves karst aquifer (Southern Spain) is a Mediterranean high-relief karst with an important geological, geomorphological, hydrogeological and ecological value. It has a spectacular landscape and a well-developed endokarst, as well as a number of important karst springs that are the origin of three important rivers in the region. In this work, we present the conceptual model of the aquifer and its mathematical model. The latter quantifies the hydrologic cycle in the aquifer, from recharge to discharge at the karst springs. The mathematical model has taken into account the particularities of karst aquifers in general (presence of a soil–epikarst layer and a well-developed network of karst conduits as well as the dichotomy of recharge, flow and discharge) and of this aquifer in particular (an important vadose zone with thickness of up to 1000 m and an important system of karst depressions with preferential recharge). The model will allow the analysis of the response of the karst system against climate change (modification of the rainfall and temperature regimes) and will assist the environmental managers in planning corrective actions.

Assessing underground hydrosystem recharge is crucial to characterizing their hydrogeological functioning. The common questions arising from a poor understanding of hydrogeological mechanism are about parts of the gross rain amount that evapotranspire and get temporarily stored within the soil. Evapotranspiration and soil water storage are largely influenced by the structure and the function of the aboveground vegetation, which is generally composed of heterogeneous forest layer in Mediterranean karstic systems. However, most models used to compute karst hydrosystem recharge rely on simplistic formulations of evapotranspiration (ET) that do not account for vegetation functioning. In this study, we used the vegetation process-based model CASTANEA to improve water transfer in the higher horizon of the karst system and recharge simulations. Effective infiltration was computed with CASTANEA or with a classical approach (based on precipitation minus ET) for a well-documented holm oak site in southern France. We then compared simulation results with outflow data measured at 33 m below ground. We found significant differences between the two calculation methods, up to 200 % of annual recharge in the case of a very dry year. The comparison of modelled effective infiltration with outflow data indicated that using CASTANEA improved assessment of the temporal dynamics of water recharge in this karst system compared to a more classical approach. Our approach constitutes a promising way to improve the simulation of karst hydrosystem recharge.

Karst aquifers provide a significant contribution to the drinking water supplies of many countries in Europe. Estimating their recharge rate, i.e. the fraction of precipitation that is turned into groundwater recharge, is an essential tool to assess usable groundwater water volumes. In this study, we extended a previously developed GIS-based recharge estimation method (APLIS) to take into account climate variability by adding a simple soil moisture routine whose parameters were a priori estimated with globally available FAO soil property data. We applied the new approach to a karst system in southern Spain and evaluated our results with spring discharge observations. To exemplify the prediction skills of the new method, we applied the five climate models from the Inter-Sectoral Impact Model Intercomparison Project to assess changes in recharge rates of the study site until the end of this century.

The data briefly presented in this paper indicate that the degree of ventilation of underground flow paths, inducing more or less degassing of the CO₂ dissolved in water, can induce a significant variation in the water mineralization of a karst spring. The presented data also provide indications about further conditions controlling time variations of carbonate dissolution parameters: (1) variations in the mixing ratio of two or several waters (from distinct subcatchment areas) with distinct chemistry; (2) land use with distinct soils (i.e. pCO₂) in the catchment area, which is also often related to the elevation of the various parts of the catchment area; (3) localized and quick infiltration vs diffuse and slow infiltration through soils. It must be mentioned here that both concentrations and fluxes of CO₂ within all parts of karst systems must be considered in order to understand water chemographs. Both are mainly controlled by soil CO₂ production and by water-recharge flux. Further models and dedicated field data are required to better quantify CO₂ concentration and fluxes in karst systems.

Gravitational dewatering of mine works—interconnected network of adits and shafts—in certain aspects of flow concentration resembles groundwater circulation in karstified rocks. To compare similarities and differences in these groundwater circulation types, hydrographs of mine waters discharging from eight adits in the past centuries excavated in crystalline, metamorphic and volcanic hard rocks of Slovakia were analysed. Discharges here were gauged on weekly bases in the periods counting several years or even several decades. After creation of discharge recessional master curves, flow component analyses revealed the presence of one or several exponential shapes of recession curves, while linear recessional mode was present only marginally or not at all. Gauging results and subsequently constructed master recession curves of 10 typical karstic springs located under the edges of karstic plateaus were compared to the previous set of results. Middle and Upper Triassic carbonates of the Slovenský Kras and Muránska planina plateaus (Slovakia) were in the past subject to intensive karstification processes, so that hydraulic behaviour of the analysed karstic springs shows typical intensive discharge response to recharge impulses, visible as steep peaks in hydrographs. Although discharges of all 10 karstic springs were gauged on daily bases, before recessional master curves creation and flow component analyses the time series were transformed to weekly data, to keep the results comparable. Contrary to the mine drains, both linear and exponential shapes of recession curves were found by flow component analyses of karstic springs. Although interconnected network of shafts and adits in mine works might be perhaps similar to conduits in karstic environment, the main difference between those two different groundwater circulation environments (karstified rocks vs. insoluble fractured solid rocks opened by mining activities) is the absence of epikarst layer in the second one. Comparison of the shapes of master recession curves here shows that the linear shapes of flow components should be linked to the influence of groundwater stored in the epikarst layer of karstified aquifers.

Analysis of natural responses of karst springs (discharge, temperature and electrical conductivity) provides reliable information on dynamics of karst aquifers. Quantitative evaluation of response times can be used to understand and characterize the factors responsible for modelling and transferring of input signal (rainfall) to different output signals of the aquifer (springs). In the present study, continuous (hourly) monitoring data of four karst springs located in Sierra de Grazalema Natural Park (Southern Spain) have been compared in order to evaluate time lags between storm event and spring responses, as well as the hydrogeological functioning of the respective systems. Results show significant differences in time lags (14–167 h) as well as non-simultaneous responses of discharge, electrical conductivity (EC) and temperature (T) to the same recharge events. Time lags between the gravity centre of each rain storm and its effect on the EC, T and discharge of the spring water seem to be more dependent on factors such as the system karst development, the flow rate at the spring or the recharge conditions (land use, soil cover, elevation) than to the magnitude of the precipitation itself.

Flash floods pose significant hazards in urbanized zones and have important implications that should probably increase due to global changes. Early warning is thus a priority that could be done by using forecast models. When such events occur on karst basins, well known for their intrinsic complexity, anisotropy and heterogeneity, the lack of knowledge regarding the various hydrodynamic behaviours involved in karst systems prevents to use physical models. A generic black box method seems thus to be adequate; specifically, artificial neural network modelling seems to be a relevant method. To model hydrosystem behaviour efficiently, neural networks need to dispose of relevant data sets constituting input and output variables, and rigorous application of regularization methods. In this study, we propose to apply two kinds of models: feedforward and recurrent neural networks to flash flood forecasting. These models are designed using a specific methodology to diminish their complexity. They are applied to the Lez karst aquifer, located in southern France, and their performances are compared. Recurrent model can be used at longer lead time for operational flash flood forecasting. Nevertheless, for short horizon of prevision, performances of feedforward model are higher than those showed by recurrent one. The comparison of both models is then necessary to guide the improvement of operational flash flood forecasting.

Both Moon and Sun induce Earth tides. Signatures of the Earth’s crustal tides could be recorded in the groundwater in the form of rise and fall of its piezometric surface. In relationship with this phenomenon, there is a scarcity of these kinds of studies in carbonate aquifers. Spectral analysis has been applied in Sierra Gorda aquifer located in the southern of Spain in order to determine the presence and statistical significance of cycles from different time data series like air temperature, barometric pressure, electrical conductivity, pH and piezometric level located in the north border of the aquifer. Diver and Hidrolab sensors to collect data every 1 and 6 h were installed in some of these springs and piezometric borehole. The piezometric data series have more than 25,000 hourly data. The period studied start in November 2010 and end in September 2013. In this site, it has been observed some spectral peaks that could be linked with crustal tides related to cyclic movement of Moon and Sun around Earth. The most significant peaks in piezometric levels that could be related to Moon and Sun show values of 12 h, 1 day, 14 days and 28 days. On the other hand, similar signal is recorded by pH and conductivity temporal data. The influence of Earth tides on pH and conductivity is less studied and would be necessary new investigations on this aquifer to confirm this possibility. The spectral signature of temperature and barometric data is quite different to others variables studied.

Air CO₂ partial pressure (Pco₂) in one of the monitored parts in Lascaux cave (Hall of the Bulls, near the entrance) is variable. For the year 2009, three major components of Pco₂ were identified: a seasonal component, a low-frequency component and a high-frequency component. As a first step to understand the presence of Pco₂ in caves, this study aims to separate these components and quantify their contributions to the Pco₂ signal. Seasonal component is calculated with a sinusoid curve fitted to the measured Pco₂. This component is subtracted from the measured Pco₂. Then, from the remaining value of Pco₂, low- and high-frequency components were separated using Fourier transform, threshold filtering of the frequency and Inverse Fourier transform. Seasonal component is the main contributor (82 % on the average); high-frequency component participates 12 % on the average. Low-frequency component is not present all the year; the average participation is 6 %. Finally, to link these three components with other measured parameters such as temperature, water flow and atmospheric pressure, hypotheses were proposed.

In this paper, we present the study results of the hydraulic behavior of the Maastrichtian karst system of the Dyr perched syncline that is situated in the north of the Algerian territory and constitutes the north horst of the Tebessa subsidence basin. Processing and analyzing the hydro-pluviometric chronicles registered for 3134 days, between September 01, 2002 and March 31, 2011 at the hydro-pluviometric station of Ain Zerga, by means of the correlative and spectral analysis method, allowed us, at first, to describe and to compare the structures of both chronological series: the chronological series of rainfall in the syncline of Dyr, considered as input (the cause) of the karst system,the chronological series of flow rate of the spring Ain Zerga, considered as its output (the effect).On the basis of signal processing, determining the signal components allowed us to demonstrate clearly the effect of the temporal variability of pluviometry on the hydraulic functioning of this karst system in a big aquifer potentiality. Indeed, this work of analysis revealed that the karst system is characterized by a weakly inertial behavior and possesses a well-developed drainage structure which constitutes a functional karstification.

When applied to hydrology, the artificial neural networks (ANN) offer multiple advantages over conventional rainfall–runoff models. It was very interesting to assess the ANN performance over one of Mount Lebanon watersheds characterized by their nonlinear hydrologic regime due to the karstic nature, geomorphology and heterogeneous precipitation of rain and snow. The time delay neural network (TDNN) models in this study were assessed for their ability to simulate highly karstified watershed with little precipitation data, especially concerning snow contribution and for their ability to simulate fluctuated river flows. The selected watershed for this study was Nahr Ibrahim watershed with an area of 329 km2 and an upper part located above 1700 m altitude taking part of the Cenomanian Plateau of Mount Lebanon. This karstic plateau is a stage for snow accumulation during winter and snowmelt during spring. The snowmelt is discharged by underneath karstic springs of Afqa and Roueiss, main contributors to Nahr Ibrahim flow. To achieve a better comprehension of the hydrologic regime, annual simulations with daily time step were conducted in this study. A simple snowmelt model was coupled with TDNN model (A) to makeup the lack of snow data. Model (A) which registered a considerable performance Nash criteria reaching 0.73 for the karstic springs and 0.66 for the watershed. However, two other methods were applied: the first, model (B), using BFI_max separation method which yielded a high performance of 0.95 and the second, model (C) with spring flows as input data which yielded 0.87. In this study, only nonlinear input output neural network was applied to avoid autoregressive models which would have definitely returned higher performances due to the long term rainfall–runoff correlation of the springs.

Modelling complex groundwater/surface water flow in karstified chalk aquifer systems both requires appropriate modelling techniques and a good knowledge of geology and discontinuities (geological and hydrogeological). This is the case for the Avre River hydro-system for which a multi-layer geological model was built, including geological and potential hydrogeological discontinuities, which then served as the basis to elaborate and calibrate the 3D hydro-system flow model. The latter through the calibrating process notably allowed explaining the presence of important spring arrays used for drinking water purposes in the central part of the basin, by the existence of a major impermeable intersecting faults system and highly fractured chalk or karst conduits which developed along lineaments and faults.

A large number of former industrial sites and landfills are responsible for aquifer contamination with chlorinated solvents in Switzerland. 16.7 % of them are located in karstic areas. But, the detection of such contaminations in springs or boreholes can be difficult because concentrations are often varying highly and rapidly. Measuring low concentrations during a few measurement campaigns is not sufficient to prove the absence of contamination. To overcome this difficulty, the performances of integrative passive samplers were investigated in the framework of the Chlorokarst project funded by the Swiss Federal Office for the Environment. Three types of devices were tested. They allow measuring time-weighted average concentrations of pollutants over long periods. Experiments in karst springs show that the Sorbicell samplers developed by the Sorbisense company were capable of measuring average concentrations over a 2-month period, matching the averages of the concentrations measured in daily snapshot samples collected with an automatic sampler taken as reference. Equipment of the springs with the Sorbicell devices was found to be easy. More difficulties were encountered when exposing the Sorbicell samplers in piezometers, because of the impact of the high fluctuations of the water column above the sampler on the filling rate. Adaptation of the device was thus carried out with the manufacturer, to reduce the effect of the water column, using air-vents and cartridges of high resistance. Satisfactory results were then obtained in terms of sampling rate. Uncertainty still remains on the estimated concentrations provided by the system since they can vary by a factor of two depending on how the volume of water that passed through the cartridge is estimated. Two other types of passive samplers were tested, the ceramic dosimeters developed at the University of Tübingen and commercialized by IMW, and the Tips developed by the AGI company. They were both found to be inappropriate to estimate reasonably well the mean concentrations in chlorinated solvents in these types of environment, even if they can still be used to detect the presence of contamination.

The main objective of this study is to perform an initial diagnosis of the presence of nitrates in carbonate-rock aquifers in the Iberian Peninsula and identify the likely sources. Geostatistical methods were employed for TOC (Total Organic Carbon) mapping the studied area. The geostatistical method of spatial estimation, known as kriging, takes into account spatial correlation between experimental data through the variogram function. Highest TOC values are located in the main ranges of the Iberian Peninsula associated to forests although the highest values on nitrates are located in the agricultural areas. Nitrate concentration in groundwater ranges from less than 1 mg/L to more than 500 mg/L. Almost 4000 samples show more than 50 mg/L of nitrates, more than 1500 samples range from 37.5 to 50 mg/L, more than 1300 samples fluctuate from 30 to 37.5 mg/L and, finally, 10,400 samples show nitrate concentrations below 30 mg/L. Farming activities have a considerable impact on the state of the environment. Results of TOC geostatistical estimation have been optimal because estimation errors have been negligible. The generalized linear model procedure has shown a highly significant negative correlation between nitrates and TOC. The major conclusion of this study is that the scarcity of TOC is related to the content of nitrates in groundwater. In this sense, certain agricultural areas of Spain showing high concentrations in the occurrence of nitrates have low TOC values due to the fact that carbonate-rock aquifers are highly vulnerable to contamination. Additionally, the results of this approach indicate that most significant aquifers of this type in Spain show a good quality status (<50 mg/L of nitrate concentration).

Since 1987, just after introduction of DRASTIC model by the committee of Environmental Protection Agency (EPA) of USA, this method has become highly popular for mapping the aquifer vulnerability analyses all around the world. Despite the criticisms raised against the selected factors’ weights of the DRASTIC method in different cases, it still utilizes as a privilege method for groundwater vulnerability assessments in alluvial aquifers. However, sometimes the DRASTIC method is subjectively modified to be more compatible with the new conditions and assumptions (modified DRASTIC). Feasibility and accessibility of data gathering for running the DRASTIC method are the reasons that made it popular for groundwater studies. By using this method, an overview of aquifer vulnerability to pollution could be drawn. In karst aquifers, methods like GOD, EPIK, PaPRIKa, LEPT, and so on are all among the highly acceptable methods used for aquifer vulnerability evaluation. However, when an alluvial and a karst aquifer are adjacent, it will cause a major concern. In this case, overall vulnerability assessments would be complicated and difficult. Regarding this fact, finding and employing a comprehensive method to evaluate this critical condition will have a great importance. In northern territories of Hamadan Province, Western Iran, thick quaternary sediments cover deep karst aquifers and formations of Miocene. Occurrences of many collapse sinkholes in the overburden alluvial section and the karst bedrock made it possible for pollutants to enter the deep aquifers of the region more easily. Therefore, it is essential to consider the role of cover-collapsed sinkholes in any try towards conducting vulnerability assessments for the region. In this study, a modified version of the DRASTIC method, in which an extra layer containing the spatial distribution of sinkholes is included, has been used. This modified version is called the Sin-DRASTIC. Results of this study showed that adding the sinkhole distribution layer to the other main layers, commonly used for running DRASTIC method, will produce more reliable results.

Libreville has been built on a peninsula, where most groundwater is brackish and far from any large surface water resources. Since the 1970s, the city has been supplied with surface water that is collected from 5 small watersheds and treated in a single main plant located in Ntoum, 40 km east of Libreville. There are few additional surface water resources available nearby, and the national water utility is desperately seeking cheap, alternative water resources. From 2007 to 2014, SEURECA and HYDROCONSEIL provided SEEG with hydrogeological expertise to develop groundwater resource near existing facilities. A thick limestone layer (Madiela limestone) had been previously drilled by oil companies. Madiela has very limited outcrops (5 km2), but proved to be highly productive (2000–10,000 m3/day per borehole), and we successfully developed a new well field. As (a) the aquifer extension is limited and (b) there is a risk of seawater intrusion, the well field was developed step-by-step and the water levels and water quality were carefully monitored (i.e., conductivity, which can indicate seawater intrusion). The aquifer storage capacity was measured through the long dry season drawdown as being 220,000 m3 per m. This is sizeable, but insufficient was the aquifer to be mined. For this reason, we proposed a MAR strategy and monitored aquifer recharge during rainfall events. This recharge proved to be highly impressive (>20 million m3/year). Such a large recharge is higher than expected from direct infiltration in such a tiny aquifer outcrop. Additional recharge mechanisms have been investigated through geophysical prospecting, and the hydrogeological model has been updated accordingly. Presently, Ntoum well field produces 55,000 m3/day of good quality water without this having any significant impact on resource quality or quantity (i.e., no significant drawdown of the water table has been recorded). In light of the recharge efficiency, we have developed a MAR strategy that includes a new well field further to the north, with 4 additional deep wells.

Knowledge of groundwater flow in mountain karst aquifers is crucial because these are main contributors to many rivers of southern Spain. Analysis of natural responses (hydrodynamic, hydrochemical, and isotopic data −δ13C_TDIC−) from two nearby karst springs located in the Sierra de Jarastepar aquifer have allowed deducing the considerable hydrogeological heterogeneity existing in the southern border of the aquifer. The natural responses of springs located in the southern edge of Jurassic limestones are different from the springs situated in Triassic dolostones. The existence of low-permeability materials in a geologically complex zone between them contributes to modulate the input signal coming from catchment area.

The Su Bentu Cave has been recently investigated to determine the geochemical features of its groundwater. The analyses have shown a low mineralization with calcium bicarbonate character. Its main composition is explained by calcite dissolution and mainly reflects both cave lithology and rainwater input. A slight increase in sodium and sulphate contents is the only exception to this pattern that may be related to the weathering of the sediments filling the cave conduits. These preliminary results have been compared with the available data on Su Gologone spring, the main karst outlet of the Supramonte aquifer (Sardinia, Italy) to whose the cave is tributary. The same alkaline–earth bicarbonate character is also observed in the spring water, but the salinity and the concentration of main ions generally increase due to longer residence time. Moreover, for the discharge point, major magnesium content indicates a dominant circulation in Jurassic dolomites outcropping nearby.

The Fertans karst system is a field site of the hydrogeological observatory “Jurassic Karst” in the French Jura Mountains. The site is located within karstified upper Oxfordian limestones. Two monitoring stations were installed for simultaneous monitoring of a spring, draining a fracture, and a borehole within the microfractured limestone giving access to the low permeability volume (LPV). A flood event was followed in June 2012, with high-frequency physicochemical (pressure, T°C, E.C) and hydrochemical measurements (major and trace elements, total organic carbon) at both stations. Infiltration (TOC, Fe, Al) and long-time residence markers (Mg) were studied in order (1) to analyze the response of the drain (spring SA) and the LPV (borehole C3) to the rainfall event, (2) to identify the origin of the flood waters, and (3) to characterize water exchange between the 2 compartments. Based on statistical analysis (PCA, DFA), it was possible to characterize different mixing end-members and to identify exchanges between drains and LPV. The hydrochemical signal of the flood was observed rapidly at the spring (3 h); in contrast, the borehole showed a much higher inertia and an arrival of infiltration water in two steps: a first peak attributed to drain contribution, and a second peak attributed to diffusively infiltrated rain water, spreading out slowly through the LPV. The infiltration water signature was typically enriched in organic carbon, Fe, and Al derived from interaction with the clay–humus complex of the surface soil. Nitrates which are often used as indicator for direct surface infiltration seemed to have accumulated over longer time periods prior to the flood in the LPV, which behaved like a diffusive nitrate source.

This study focuses on determining the hydrodynamic and hydrogeochemical behavior of the vadose zone of Lascaux karst (Dordogne, France). This work is of particular interest for the conservation of the famous prehistoric paintings of the Lascaux Cave. Indeed, unsustainable infiltration into the cave influences the microclimate parameters (temperature, humidity) and may play a role in aerologic phenomena (condensation, drying) that can affect the decorated walls. A continuous monitoring device for physical and chemical parameters (conductivity, pH, temperature, dissolved O₂) and fluorescence of organic matter are installed in the epikarstic spring located inside the cavity. In addition, weekly samples are performed at the epikarstic and Haute Fageotte springs. Weekly rainfall (major ions, water isotopes) and soil water (major ions, organic carbon) samples are performed to determine the input chemical signal in the karst system. The results show that water with shorter or longer residence time can be identified during the floods, considering electrical conductivity and the dissolved organic carbon as natural tracers. Moreover, when the system is highly water saturated, water with long residence time is solicited highlighting an increase of the area participating to the flow at the epikarstic emergence. The study of the calco-carbonic equilibrium of the epikarstic spring also confirms these observations. The calco-carbonic equilibrium shows interannual and seasonal variations related to climatic conditions, carbon dioxide concentration in soils and epikarst, and the flow conditions in the vadose zone. The relations between SI_c and PCO_2eq allow us to recognize the climate influence on the recharge geochemical signal of the Lascaux karst. It would be useful to estimate the global warming impact on the geochemistry of karst water.

The Maro Spring, near Nerja, southern Spain, drains a Triassic carbonate aquifer. It presents a typical karstic behaviour. We have compiled more than 220 pH values of water from this spring and a nearby well. The spatial variation of this variable suggests a CO₂ degassing effect as far as the groundwater flow gets near the spring. The average pH seasonal variation indicates a maximum during autumn and a minimum in spring. This can be explained by water degassing related to the start of the period of convective ventilation in vadose voids, as happens in the important Nerja Cave located nearby. There also seems to be an effect of downward gas diffusion when the soil respiration is at its peak and the ventilation of the vadose voids is nearly inhibited. These circumstances suggest that Maro Spring water can be spatially linked with unknown cavities. The second phase of this study is the identification of some of these voids by the way of combination of two gravity profiles of 200 m, one designed as a test of the method and the other for prospecting the voids. The link between hydrochemical and geophysical methods is the main aim of this study as such a transdisciplinary approach is not frequently used in hydrogeology.

At southern Cordoba Province (S Spain), an evaporitic karst plateau drained by brine springs is located. A periodic monitoring of discharge rate, EC, water temperature, and pH was performed in one of them (Lower Anzur spring) and water samples were collected for chemical analysis. Physicochemical data were used to perform a principal component analysis (PCA) to characterize the functioning of the system. Temporal evolution of the controlled parameters reveals a markedly karst behavior. PCA has defined two principal factors, one related to salinity and other linked to infiltration processes (NO₃−, Ca2+). The slight thermal anomaly and the high mineralization registered indicate the existence of ascending regional groundwater flows of long residence time, which would converge into the spring, mixed with recently infiltrated water that circulated through a conduit network formed in the evaporite rocks.

The karst aquifers in the San Franciscan depression belong to the sandstone aquifer and subjected to intense fresh water pumping. The Corrente River provides nearly 30 % of the São Francisco River’s water flow. The main objective of the present paper was to define sources and distribution of dissolved elements and to describe the geochemical processes that govern their mobility within the Urucuia Aquifer. Water samples are classified into three groups, depending on the dominant weathering process. When carbonate dissolution dominates waters are of bicarbonate–calcium-type, whereas, when the atmospheric precipitation signal is present, the samples in siliciclastic terrain are mostly of Cl−–Na+ type. Ground waters reflect bicarbonate—mixed-type, with the highest dissolved concentrations. In contrast to major elements, trace elements, including rare earth elements (REEs), show seasonal behavior: their concentrations increase in the beginning of the wet season, due to re-mobilization and release into the solution of adsorbed elements from the system and the atmospheric dust. The total dissolved REE concentration (800–7500 ng L−1) is one order of magnitude more concentrated in karst than in siliciclastic rocks.

The adequate management of small aquifers located in structurally complex areas requires detailed geological and hydrogeological knowledge of the system. The analysis may include features related to the aquifers´ 3D geometry, their lateral connection with other aquifers, their hydraulic parameters, and their storage and recovery capacities during dry periods. To accomplish such a study is complex, and it involves even more uncertainties in the case of karst aquifers due to their special features. In this paper we present a multidisciplinary hydrogeological approach to explore a carbonate aquifer of southern Spain subjected to intensive exploitation. The study allowed us to redefine its geometry and its limits through the acquisition of geological and geophysical (gravity) data. New hydrodynamic, hydrogeochemical and isotopic information led to a new conceptual model and the definition of guidelines for a more efficient management.

Hydrodynamic and hydrochemical responses of Toulon springs are examined to identify the functioning of the karst system. First, analysis of the recession curve coupled to univariate and bivariate analyses is conducted to determine storage capacity and relationship between rainfall and discharge. Results show a complex system which could provide fast hydrodynamic responses to rainfall solicitation, but have an ineffective drainage network and then high storage capacity. In addition, temporal evolution of hydrochemical parameters leads to identify quick variation of hydrochemical responses during flood events. Furthermore, a principal component analysis (PCA) is conducted on 61 samples and confirms that springs are fed with waters from different origins.