Time constant of hydraulic-head response in aquifers subjected to sudden recharge change: application to large basins

Analytical formulae are proposed to describe the first-order temporal evolution of the head in large groundwater systems (such as those found in North Africa or eastern Australia) that are subjected to drastic modifications of their recharge conditions (such as those in Pleistocene and Holocene times). The mathematical model is based on the hydrodynamics of a mixed-aquifer system composed of a confined aquifer connected to an unconfined one with a large storage capacity. The transient behaviour of the head following a sudden change of recharge conditions is computed with Laplace transforms for linear one-dimensional and cylindrical geometries. This transient evolution closely follows an exponential trend exp(?t/τ). The time constant τ is expressed analytically as a function of the various parameters characterizing the system. In many commonly occurring situations, τ depends on only four parameters: the width a _c of the main confined aquifer, its transmissivity T _c, the integrated storage situated upstream in the unconfined aquifer M?=?S _u a _u, and a curvature parameter accounting for convergence/divergence effects. This model is applied to the natural decay of large aquifer basins of the Sahara and Australia following the end of the mid-Holocene humid period. The observed persistence of the resource is discussed on the basis of the time constant estimated with the system parameters. This comparison confirms the role of the upstream water reserve, which is modelled as an unconfined aquifer, and highlights the significant increase of the time constant in case of converging flow.     

Assessment of textural variational pattern and electrical conduction of economic and accessible Quaternary hydrolithofacies via geoelectric and laboratory methods in SE Nigeria: A case study of select locations in Akwa Ibom State

Textural variational pattern of economic and accessible Quaternary aquifer repositories and its conductivity in the south-eastern Nigeria have been assessed through the integration of vertical electrical sounding and laboratory measurements. The results have shown the lithological attributes, pore-water and amount of residual clay minerals in the assumed clean sand; mechanism of charge fixation at the fluid - surface interface; intricate geometry of pores and pore channels; formation’s ability to transmit pore-water and cation exchange capacity.The connections of electrical and hydraulic properties and their distributions have been established. The average interface conductivity contributed by residual clay minerals in assumed clean sands of the aquifer repositories in the study area have been estimated as 30µS/m. Intrinsic average porosity and formation factor have been respectively deduced as 12% and 14.75. Comparing the simulated aquifer formation factor obtained from the observed porosity data with the observed aquifer formation factor, indicates the that study area has 0.5 ≤ a ≤ 0.8 pore geometry factor and 1.5 ≤ m ≤ 2.0 cementation factor as the best fitting values. The interrelations between aquifer parameters have been established through different plots and the aquifer have been empirically proved to be associated with residual clay minerals as the interface conductivity C_q is not equal to zero. The wide ranges of parameters estimated are an indication of variations in grain size. The estimated intrinsic average porosity, formation factor and the average BQ_v are viable in characterizing the aquifer flow dynamics and contaminant modelling in the associated aquifer sands For low pore geometry factors a (0.2) and low cementation factor m (0.5) the formation factor remains fairly constant. However, marked variability is noticed at higher a (1.0) and m (2.5). Despite the observed variability in formation factors at the indicated porosities, the spatial or geometrical spread of the formation factor remains unchanged in the aquifer units. The Tables for geoelectric and petrophysical parameters and the associated mathematical models generated in this study can be used for groundwater contaminant modelling and simulation of pore space parameters with reasonable accuracy.     

Toward reliable calibration of aquifer hydrodynamic parameters: characterizing and optimization of arid groundwater system using swarm intelligence optimization algorithm

Despite advanced development in computational techniques, the issue of how to adequately calibrate and minimize misfit between system properties and corresponding measurements remains a challenging task in groundwater modeling. Two important features of the groundwater regime, hydraulic conductivity (k) and specific yield (S _y), that control aquifer dynamic vary spatially within an aquifer system due to geologic heterogeneity. This paper provides the first attempt in using an advanced swarm-intelligence-based optimization algorithm (cuckoo optimization algorithm, COA) coupled with a distributed hydrogeology model (i.e., MODFLOW) to calibrate aquifer hydrodynamic parameters (S _y and k) over an arid groundwater system in east Iran. Our optimization approach was posed in a single-objective manner by the trade-off between sum of absolute error and the adherent swarm optimization approach. The COA optimization algorithm further yielded both hydraulic conductivity and specific yield parameters with high performance and the least error. Estimation of depth to water table revealed skillful prediction for a set of cells located at the middle of the aquifer system whereas showed unskillful prediction at the headwater due to frequent water storage changes at the inflow boundary. Groundwater depth reduced from east toward west and southwest parts of the aquifer because of extensive pumping activities that caused a smoothening influence on the shape of the simulated head curve. The results demonstrated a clear need to optimize arid aquifer parameters and to compute groundwater response across an arid region.     

A comparative study of hydraulic conductivity estimations using geostatistics

Three approaches for estimating the hydraulic conductivity (K) of the Trifa aquifer, Morocco were investigated: (1) kriging of the K values obtained from pumping tests, (2) cokriging of the pumping test data with electrical resistivity data as a secondary variable, and (3) cokriging of the pumping test data with the slope of the water table. Gauss-transformed values of the variables are used because they provide more robust variograms and transformed values of the primary and secondary variables show correlations higher than the raw values, which is beneficial in cokriging. In cokriging with electrical resistivity, two zones are considered since the geological deposits are different from the north to the south of the aquifer, which is reflected in different correlations between the variables. Comparison of the three approaches is based mainly on the estimation errors, and to a lesser degree on the cross-validations of the corresponding variogram models and general considerations, like the measurements’ reliability and aquifer make-up. The best-estimated K is given by cokriging with the slope of the water table and is therefore preferred for further use in groundwater flow modeling. Thus, electrical resistivity or the slope of the water table can both be used as secondary variables to estimate K, especially in heterogeneous aquifers with lateral variations in lithology, as is the case of the Trifa aquifer.     

Upscaling of transmissivity,derived from specific capacity: a hydrogeomorphological approach applied to the Doon Valley aquifer system in India

Transmissivity (T) is one of the most important parameters in groundwater studies, and is generally estimated from pumping tests. T can also be deduced from abundantly available specific-capacity (Q/s) data by using analytical and/or empirical approaches, further upscaled by geostatistical methods. A different, remote sensing based, hydrogeomorphological approach is proposed, to upscale T from point- or well-scale to aquifer-scale, and it is applied to the piedmont alluvial aquifer system of Doon Valley in India. In the first step, Q/s and T data-pairs available from aquifer tests were used to establish an empirical, logarithmic relation. Subsequently, satellite imagery along with available data from published and unpublished maps, literature sources and ground surveys were used to divide the aquifer system into major hydrogeomorphological domains that control the groundwater occurrence and flow. Then, the T data derived from Q/s (using the empirical relation) and that available from pumping tests at well-scale were upscaled to aquifer-scale by averaging the T values within each hydrogeomorphological domain. Such a stratification approach is especially useful in areas where availability of only a few data-pairs of known Q/s and T limit the use of geostatistical techniques. A comparative study of the published empirical relations between Q/s and T in various hydrogeologic settings revealed that the relation obtained for Doon Valley aquifer system is close to that found for a similar alluvial aquifer system in Morocco.     

Estimating groundwater evapotranspiration rates using diurnal water-table fluctuations in a semi-arid riparian zone

In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ET_G) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ET_G, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ET_G to potential evapotranspiration (PET), K _c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K _c, in semi-arid rangelands. Before vegetation senescence, K _c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K _c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ET_G is primarily from estimates of specific yield (S _y), which is difficult to quantify in heterogeneous sediments. ET_G values may be more reliable because the range of acceptable S _y is smaller than K _c and S _y does not change with vegetation type or soil moisture.     

How water use of <Emphasis Type="Italic">Salix</Emphasis><Emphasis Type="Italic">psammophila</Emphasis> bush depends on groundwater depth in a semi-desert area

To investigate the groundwater levels changes effects on the transpiration of Salix psammophila (S. psammophila) bush, systemic measurements of meteorological conditions, sap flow of S. psammophila, soil water contents and groundwater levels were conducted in the Hailiutu River catchment, NW of China. Based on the collected field data, Hydrus-1D software package was used to calibrate water movement for root uptake in the saturated–unsaturated zone. The soil hydraulic parameters and root uptake function parameters were calibrated. The simulated results of soil water contents and sap flow fitted well with the observed ones. Based on the calibrated hydraulic parameters, different groundwater levels were imposed at the low boundary to simulate the groundwater levels changes effects on the transpiration. The relationship between ratio of actual transpiration and potential (T/T _p) and groundwater water table depth was established. The results shows that the ratio of actual transpiration and potential transpiration decreases with groundwater table depth increase as inverse ‘S’ shape. And the turn point is corresponding to the extinct depth, i.e., no groundwater contribution to S. psammophila transpiration. To further verify this phenomenon is universal, the soil hydraulic parameters were replaced with the other five groups in the calibrated forward model. The results confirmed the similar changes of T _a/T _p with the groundwater levels changed, i.e. inverse ‘S’ shape. However, the extinction depth is different corresponding to different soil hydraulic parameters. So, the research results indicated the relationship between transpiration and groundwater levels is non-linear function.     

Estimated volume of water in shallow wells of Ekiti State,Southwestern Nigeria: implications on groundwater sustainability

Volumes of water in shallow wells of Ekiti State Southwestern Nigeria was estimated during the rainy and dry seasons of 2017 to categorize the area into different groundwater potential zones and to scrutinize it for groundwater sustainability and development. Locations of the wells were measured using etrex 12 Channel GPS while dip meter was employed for the water levels and depths of wells. The volume of water in a well was estimated employing V = πr²h (r and h are radius and water column of well, respectively). The wells in the area have low water storage (av. 6.91m³ and 2.70m³ in rainy and dry seasons, respectively). The study area had sufficient quantity of water in the rainy season to meet domestic, agricultural, and industrial requirements as deficiency was met from rainfall replenishment. Groundwater potential evaluation revealed that majority of the study area fell into very poor to poor water categories. Groundwater sustainability and development in the study area is a herculean task due to uncoordinated sitting of wells, low storage of water in the aquifers, and erratic occurrence of the groundwater. Hygiene education should be intensified in the area to forestall the risks post by the principal elements of fecal oral disease transmission.     

Complementary use of tracer and pumping tests to characterize a heterogeneous channelized aquifer system in New Zealand

The combined use of pumping and tracer test data enabled the derivation of equivalent average hydraulic conductivities (K_avg) for each test in a heterogeneous channelized alluvial aquifer, whereas K values of the preferential flow paths were two orders of magnitude higher. Greater and earlier drawdown was generally observed along preferential flow lines in a pumping test, within an array of 21 wells. The study aim was to characterize hydraulic properties of a channelized aquifer system in New Zealand by combining tracer and pumping test data. Estimates were able to be made of the percentage of highly permeable channels within the profile (～1.2%), effective porosity that reflected the maximum fraction of highly permeable channels within the aquifer (?_eff–pc ～0.0038), and flows through highly permeable channels (～98%) and the sandy gravel matrix material (～2%). Using ?_eff–pc, a tracer test K_avg value (～93 m/day) was estimated that was equivalent to pumping test values (～100 m/day), but two orders of magnitude smaller than K calculated solely from transport through permeable channels (K_pc ～8,400 m/day). Derived K values of permeable and matrix material were similar to values derived from grain size distribution using the Kozeny-Carman equation.     

Seasonal disparity in the co-occurrence of arsenic and fluoride in the aquifers of the Brahmaputra flood plains,Northeast India

Arsenic (As) and fluoride (F^?) in groundwater are increasing global water quality and public health concerns. The present study provides a deeper understanding of the impact of seasonal change on the co-occurrence of As and F^?, as both contaminants vary with climatic patterns. Groundwater samples were collected in pre- and post-monsoon seasons (n = 40 in each season) from the Brahmaputra flood plains (BFP) in northeast India to study the effect of season on As and F^? levels. Weathering is a key hydrogeochemical process in the BFP and both silicate and carbonate weathering are enhanced in the post-monsoon season. The increase in carbonate weathering is linked to an elevation in pH during the post-monsoon season. A Piper diagram revealed that bicarbonate-type water, with Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations, is common in both seasons. Correlation between Cl^? and NO₃ ^? (r = 0.74, p = 0.01) in the post-monsoon indicates mobilization of anthropogenic deposits during the rainy season. As was within the 10 µg L^?1 WHO limit for drinking water and F^? was under the 1.5 mg L^?1 limit. A negative correlation between oxidation reduction potential and groundwater As in both seasons (r = ?0.26 and ?0.49, respectively, for pre-monsoon and post-monsoon, p = 0.05) indicates enhanced As levels due to prevailing reducing conditions. Reductive hydrolysis of Fe (hydr)oxides appears to be the predominant process of As release, consistent with a positive correlation between As and Fe in both seasons (r = 0.75 and 0.73 for pre- and post-monsoon seasons, respectively, at p = 0.01). Principal component analysis and hierarchical cluster analysis revealed grouping of Fe and As in both seasons. F^? and sulfate were also clustered during the pre-monsoon season, which could be due to their similar interactions with Fe (hydr)oxides. Higher As levels in the post-monsoon appears driven by the influx of water into the aquifer, which drives out oxygen and creates a more reducing condition suitable for reductive dissolution of Fe (hydr)oxides. An increase in pH promotes desorption of As oxyanions AsO₄ ^3? (arsenate) and AsO₃ ^3? (arsenite) from Fe (hydr)oxide surfaces. Fluoride appears mainly released from F^?-bearing minerals, but Fe (hydr)oxides can be a secondary source of F^?, as suggested by the positive correlation between As and F^? in the pre-monsoon season.     

Application of electrical resistivity method in estimating geohydraulic properties of a sandy hydrolithofacies: a case study of Ajali Sandstone in Ninth Mile,Enugu State,Nigeria

Geoelectric investigation using vertical electrical sounding (VES) (Schlumberger electrode configuration) was carried out in 14 locations at Ninth Mile area, southeastern Nigeria to determine the variations and interrelationship of some geoelectric and geohydraulic parameters of a sandstone hydrolithofacies. The measured resistivity data were interpreted using manual and computer software packages, which gave the resistivity, depth, and thickness for each layer within the maximum current electrodes separation. The aquifer resistivity values range from 86.56 to 4753.0 Ωm with 1669.40 Ωm average value. The values of water resistivity from borehole locations close to the sounding points range from 79.49 to 454 .55 Ωm and averaging about 264.7 Ωm. Porosity values of the sandy aquifer range from 30.19 to 34.20%. Fractional porosity values range from 0.3019 to 0.3292, while the tortuosity values vary between 2.91 and 22.85. The geohydraulic parameters estimated vary across the study area. Formation factor ranges from 0.28 to 15.29, hydraulic conductivity ranges from 1.21 to 66.54 m/day which, however, influences the natural flow of water in the aquifer while tortuosity values range from 2.91 to 23.27. The contour maps clearly show the variation of these parameters in the subsurface and the plots show their relationship and high correlation coefficients with one another. The results of this study have revealed the geological characteristics of the subsurface aquifer, established the influence on the amount of groundwater, and proposed a strategy for the management and exploitation of groundwater resources in the area and other aquiferous formations.     

Investigation into the change of the porosity parameter during transition from laboratory to reservoir conditions

The purpose of the investigation is to reveal the dependences of P _p = f(C _p) on reservoir conditions and the lithological composition of rocks. The samples were studied using a set of lithological-petrographic investigations. To obtain the dependences on thermobaric conditions, 90 samples of different porosities (C _p) of 15, 20, and 25% were collected. As a result, the general pattern of the change in the rock resistivity during the transition from atmospheric conditions of measuring to reservoir conditions was established. Dependences of porosity parameter P _p on porosity coefficient C _p were obtained for three values of formation water salinity and three reservoir conditions. The measurement errors of the porosity parameter P _p were calculated using dependences obtained under atmospheric conditions.     

Evolution of lacustrine basin in relation to variation in palaeowater depth and delta development: Neogene Bohai Bay Basin,Huanghekou area,northern China

This paper presents revision of the Neogene chronostratigraphic framework of the Huanghekou area in the Bohai Bay Basin, northern China, on the basis of integration of palaeomagnetic data and Neogene seismic stratigraphy. The modern Lake Dongting was selected for analyses of bottom sediments, water depth and elemental composition. Four elements, namely Al, V, Ni and Ga with R ² value larger than 0.7, were chosen to establish a quantitative relationship (F _P) between elemental composition and water depth of bottom sediments. A water depth of ~2.4 m was identified as an accumulation depth of Candoniella albicans, which is used to derive environmental variable (Φ) of formula F _P. Candoniella albicans is also found within the Neogene well W10 in the Huanghekou area. Considering 2.4 m as D value in formula F _p and measured element values at different depths of W10, Φ values were obtained at different depths. The quantitative palaeowater depths of each drilling well were estimated for the first time in this area by considering elemental composition of chip samples of four drilling wells in the Huanghekou area, which are directly iterated to the F _F. Palaeowater depth reconstruction of the Neogene in the Huanghekou area indicates an initial deepening trend and a later shallowing trend during the evolution, with average and deepest bathymetry at ~2.3 and ~4.8 m, respectively. Frequent fluctuations of palaeowater depth control the sand dispersal pattern in a shallow delta during the lower part of the Lower Member of Minghuazhen Formation.     

Modelling the effects of porous media deformation on the propagation of water-table waves in a sandy unconfined aquifer

This paper examines the influence of porous media deformation on water-table wave dispersion in an unconfined aquifer using a numerical model which couples Richards’ equation to the poro-elastic model. The study was motivated by the findings of Shoushtari et al. (J Hydrol 533:412–440, 2016) who were unable to reproduce the observed wave dispersion in their sand flume data with either numerical Richards’ equation models (assuming rigid porous media) or existing analytic solutions. The water-table wave dispersion is quantified via the complex wave number extracted from the predicted amplitude and phase profiles. A sensitivity analysis was performed to establish the influence of the main parameters in the poro-elastic model, namely Young’s modulus (E) and Poisson’s ratio (ν). For a short oscillation period (T?=?16.4 s), the phase lag increase rate (k _i) is sensitive to the chosen values of E and ν, demonstrating an inverse relationship with both parameters. Changes in the amplitude decay rate (k _r), however, were negligible. For a longer oscillation period (T?=?908.6 s), variations in the values of E and ν resulted in only small changes in both k _r and k _i. In both the short and long period cases, the poro-elastic model is unable to reproduce the observed wave dispersion in the existing laboratory data. Hence porous media deformation cannot explain the additional energy dissipation in the laboratory data. Shoushtari SMH, Cartwright N, Perrochet P, Nielsen P (2016) The effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer: sand flume experiments and modelling. J Hydrol 533:412–440.     

Hydrogeologic and hydraulic characterization of aquifer and nonaquifer layers in a lateritic terrain (West Bengal,India)

The hydrogeologic and hydraulic characteristics of a lateritic terrain in West Bengal, India, were investigated. Test drilling was conducted at ten sites and grain-size distribution curves (GSDCs) were prepared for 275 geologic samples. Performance evaluation of eight grain-size-analysis (GSA) methods was carried out to estimate the hydraulic conductivity (K) of subsurface formations. Finally, the GSA results were validated against pumping-test data. The GSDCs indicated that shallow aquifer layers are coarser than the deeper aquifer layers (uniformity coefficient 0.19–11.4). Stratigraphy analysis revealed that both shallow and deep aquifers of varying thickness exist at depths 9–40 and 40–79 m, respectively. The mean K estimates by the GSA methods are 3.62–292.86 m/day for shallow aquifer layers and 0.97–209.93 m/day for the deeper aquifer layers, suggesting significant aquifer heterogeneity. Pumping-test data indicated that the deeper aquifers are leaky confined with transmissivity 122.69–693.79 m²/day, storage coefficient 1.01?×?10^?7–2.13?×?10^?4 and leakance 2.01?×?10^?7–34.56?×?10^?2 day^?1. Although the K values yielded by the GSA methods are generally larger than those obtained from the pumping tests, the Slichter, Harleman and US Bureau Reclamation (USBR) GSA methods yielded reasonable values at most of the sites (1–3 times higher than K estimates by the pumping-test method). In conclusion, more reliable aquifers exist at deeper depths that can be tapped for dependable water supply. GSA methods such as Slichter, Harleman and USBR can be used for the preliminary assessment of K in lateritic terrains in the absence of reliable field methods.     

Groundwater chemical and fecal contamination assessment of the Jerba unconfined aquifer,southeast of Tunisia

Located in the southeast of Tunisia, on the Mediterranean Sea, Jerba Island has a semiarid climate condition. The surface water scarcity has made groundwater the main source to supply the domestic, touristic, and agricultural water demand. Unconfined aquifer is a vulnerable costal aquifer system that undergoes several phenomena. This work aims at assessing the geochemical and bacteriological groundwater quality, defining groundwater pollution sources and promoting sustainable development and effective management of groundwater resources in Jerba Island. Data were collected after the wet season in 2014 from 79 wells. Electric conductivity, pH, TDS, and major and fecal tracers (total coliforms, thermotolerant coliforms, Escherichia coli, and Salmonella) were analyzed. Geochemical modeling including the relationships between geochemical tracers Na⁺ vs. Cl^?, Ca²⁺ vs. Cl^?, K⁺ vs. Cl^?, representative ionic ratios (Br^?/Cl^?, Na⁺/Cl^?, Mg²⁺/Ca²⁺), and statistical analysis were used to specify major process contributing to groundwater pollution and main factors controlling groundwater mineralization in the island. Groundwater varieties were hydrochemically classified into three types in terms of salinity values: group 1 (8.86%) to fresh water, group 2 (27.84%) to brackish water, and group 3 (63.29%) belongs to saline water. In addition, groundwater quality revealed high concentrations in chemical pollution tracers (Na⁺, Cl^?, SO₄ ^2?, and NO₃ ^?) and fecal tracers. Besides, most of the sampled wells were contaminated with nitrate (50.63%). Also, thermotolerant coliforms and E. coli were detected in all groundwater samples (96.2% of wells). Results indicated that the Jerba shallow aquifer was under serious threat from both natural and anthropogenic contamination. However, the wild discharge of domestic effluents, septic tanks, and sewage were the main origins of underground water contamination in Jerba Island. The reduction of fecal sources, through constructing normalized latrines is thus recommended.     

Comparison of the magnetic properties of leading and following spots and the overlying ultraviolet emission

SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α _min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α _min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α _min and 〈α〉 decrease with growth in the maximum magnetic field B _max in both leading and following spots. The presence of a positive correlation between B _max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C ₃₀₄. Spots satisfying certain conditions display a positive correlation between C _304?L and 〈α _L 〉 for the leading (L) spots, and between C _304?L /C _304?F and l _L /l _F , where l _L (l _F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.     

Characterization of flow and transport dynamics in karst aquifers by analyzing tracer test results in conduits and recharge areas (the Egino Massif,Basque Country,Spain): environmental and management implications

Karst aquifers contribute to supplying drinking water to almost a quarter of the world´s population. Their complex dynamics requires specific approaches aimed at recognizing their singularities, analyzing its vulnerability, and ensuring water resources quality. In this paper, the results of processing and modeling five breakthrough tracer curves obtained under different hydrodynamic conditions in the main conduit of Egino karst aquifer (Basque Country, Spain) are analyzed together with those involving pressure injections of the tracer in the saturated zone of the karst massif recharge area. In the conduit, transport is immediate and highly efficient (recovery rates above 84% and dispersion coefficients from 15.04 to 84.35 m²/min); tracer retentions increase as flow rates decrease and no significant contributions to its surroundings are observed. In contrast, tracer transport from the massif recharge area is more complex: after injection at a pressure of 1 MPa, most tracer remains in the surrounding of the injection borehole, retained in a saturated medium of low effective fracture porosity (? _f ?=?1.02?×?10^?4, assuming a radial divergent flow model); subsequently, the main tracer mobilization to the spring was registered with the first rains, with 0.088 m/min mean velocity and high concentrations per unit mass being injected (C _p /M₀?=?0.03 mg/L/kg), which is evidence that the tracer reaches soon the karst conduit network. In any case, a decreasing tracer presence is registered at the injection zone during a hydrological cycle. In both cases, the observed non-linearity of transport processes should be considered in the development of vulnerability approaches, modeling efforts, and mapping. Furthermore, in the case of karst massif recharge areas, as the presence of pollutants may have a significant impact on the springs and persist over time, their management and protection needs must be revised in each specific site. Simultaneously, quality-monitoring programs at the springs must be adapted to the aquifers recognized dynamics.     

Groundwater flow dynamics of weathered hard-rock aquifers under climate-change conditions: an illustrative example of numerical modeling through the equivalent porous media approach in the north-western Pyrenees (France)

A numerical groundwater model of the weathered crystalline aquifer of Ursuya (a major water source for the north-western Pyrenees region, south-western France) has been computed based on monitoring of hydrological, hydrodynamic and meteorological parameters over 3 years. The equivalent porous media model was used to simulate groundwater flow in the different layers of the weathered profile: from surface to depth, the weathered layer (5?·?10^?8?≤?K?≤?5?·? 10^?7 m s^?1), the transition layer (7?·?10^?8?≤?K?≤?1?·? 10^?5 m s^?1, the highest values being along major discontinuities), two fissured layers (3.5?·?10^?8?≤?K?≤?5?·?? 10^?4 m s^?1, depending on weathering profile conditions and on the existence of active fractures), and the hard-rock basement simulated with a negligible hydraulic conductivity (K = 1 10 ^?9 ). Hydrodynamic properties of these five calculation layers demonstrate both the impact of the weathering degree and of the discontinuities on the groundwater flow. The great agreement between simulated and observed hydraulic conditions allowed for validation of the methodology and its proposed use for application on analogous aquifers. With the aim of long-term management of this strategic aquifer, the model was then used to evaluate the impact of climate change on the groundwater resource. The simulations performed according to the most pessimistic climatic scenario until 2050 show a low sensitivity of the aquifer. The decreasing trend of the natural discharge is estimated at about ?360 m³ y^?1 for recharge decreasing at about ?5.6 mm y^?1 (0.8 % of annual recharge).     

Characteristics of deuterium excess parameters for geothermal water in Beijing

This study investigates the characteristics of geothermal water in 10 geothermal fields in Beijing. The relationships between the deuterium excess parameter (d) and temperature, depth, age of geothermal groundwater, groundwater flow field, and Eh were investigated using geothermal groundwater samples. Results showed that (1) the average d value of geothermal water is 5.4, whereas that of the groundwater in normal temperature is 6.04. The differences are induced by the oxygen isotope exchange during the water–rock interaction, which may be more easily completed in geothermal water than in cold groundwater. (2) The d value increases remarkably with the age of the geothermal groundwater. The d value increases from 11.2 to 14.6 when the age of the geothermal water is 12,760 ± 130 a and 38,960 ± 630 a, respectively. Moreover, the isotope heat exchange for composition of the hydrogen and oxygen isotopes in the geothermal groundwater proceeds sufficiently with time. (3) The d value decreases from 5.72 to 3.03 when the depth increases from 125.13 to 3221 m. Generally, in the same area, the d value decreases with depth because the temperature is increasing. (4) The d value of the groundwater gradually reduces from the northern recharge area to the southern discharge area. The average d value is 7.31 in the northern recharge area and 5.68 in the middle Beijing Depression, whereas the d value in the southern area of Fengheying is ?9.20. The larger difference in d values between the recharge and discharge areas is due to the slower velocity of underwater flow, which induces longer time for oxygen exchange. (5) The relationship between the d and Eh is complex. When Eh is <200 mV, the d value of the geothermal water decreases with the decrease in Eh. When Eh is higher than 200 mV, the d value increases slightly with the decrease in Eh. The study of the characteristics of deuterium excess parameters for geothermal water could provide a scientific isotopic evidence for assessment and exploitation measures in geothermal groundwater systems.