Springs are sources of freshwater supply. Furthermore, they can also deliver valuable insight into the hydrogeologic processes of a mountainous region, a natural conservation area or a remote study site with no wells. In order to assess the appearance, peculiarities, quality, stability, longevity and resilience of springs and related ecosystems, they need to be regarded in the context of basin-scale groundwater flow systems. The application of spring data evaluation on a basin scale was demonstrated via the carbonate system of Transdanubian Mts., Hungary. The readily measurable physical parameters of springs, the elevation of spring orifice, temperature and volumetric discharge rate provided reasonable classification and characterisation of springs and the related groundwater flow systems. Applying these parameters seemed prospective in a basin-scale understanding of flow systems in data-scarce regions, as monitoring discharge rate and water temperature are cost-effective, requiring no specific tools and analysing procedures. The combined cluster and discriminant analysis (CCDA) can handle uneven data distribution, unequal length and spacing of time series, data gaps, and consider the time-dependent variability of parameters. The optimal number of groups can be determined based on frequently sampled springs (or other entities). The less monitored springs (or other entities) can be classified using a similarity-based approach and linear discriminant analysis (LDA). Diagnosing the relation of springs to groundwater flow systems can advance sustainable water resources management, considering the ecological water needs maintaining various ecosystem services, therefore enhancing the resilience of springs and groundwater-dependent ecosystems.
Lithium (Li) isotopes have shown large potential in tracing weathering in various water bodies, but there is limited study on Li isotopes in subsurface conditions where CO2 has been largely consumed. In this study, we use a thick sandstone aquifer in the Ordos Basin, NW China, as a natural setting to investigate the behaviors of Li isotopes in hydrogeochemical conditions with different concentrations of dissolved CO2. For young groundwater in the recharge area (group R) where CO2 is abundant (mean PCO2 = 10-2.5 atm), clay formation accompanying with weathering leads to the enrichment of ⁷Li in groundwater. The four deep samples in the recharge area have uniform Li/Na ratios (with a mean of 2.52 μmol/mmol) and δ⁷Li (with a mean of 25.0‰), corresponding to a mean Li removal rate of 81.2% compared with the sandstone leachate. For groundwater in the shallow part of the discharge area (group D1), Li was firstly removed by clay formation during weathering in the recharge area and was later removed by physisorption when CO2 becomes much lower (mean PCO2 = 10-3.1 atm). Different degrees of weathering lead to a wide range of δ⁷Li varying from 19.7‰ in the deepest well to 33.0‰ in the shallowest well. The proportion of Li removal caused by physisorption is found to increase with groundwater age. After the stage of Li removal by adsorption, Li was released in the deeper part of the discharge area (group D2), and the positive correlation of δ⁷Li versus Li/Na is explained by a ternary mixing model. The endmember of water brought by cation exchange is inferred to have a heavier δ⁷Li than sandstone leachate, demonstrating that cation exchange could cause an enrichment of ⁷Li in water. This study enhances our understanding of the controlling factors of Li isotopes in deep groundwater with low dissolved CO2, which have implications for the application of Li isotopes in subsurface water.
Salinization of groundwater has endangered e.g. drinking water supply, agricultural cultivation, groundwater-dependent ecosystems, geothermal energy supply, thermal and hydrocarbon well production to a rising degree. In order to investigate the problem of coupled topography- and salinity-driven groundwater flow on a basin-scale, a systematic simulation set has been carried out in a synthetic numerical model. Detailed sensitivity analysis was completed to reveal the effect of the salinity, permeability, permeability heterogeneity and anisotropy, mechanical dispersivity and water table head on the salt concentration field and the flow pattern. It was established that a saline dome with slow inner convection formed beneath the discharge zone in the base model due to the topography-driven regional fresh groundwater flow. An increase in the salinity or the anisotropy or decrease in the water table variation weakens the role of the forced convection driven by the topography, thus facilitating the formation of a saline, dense, sluggish layer in the deepest zone of the basin. In the studied parameter range, the variation in permeability and dispersivity affects the shape of the saltwater dome to less degree. However, the decrease in permeability and/or the increase in dispersivity advantage the homogenization of the salt concentration within the saline zone and strengthen the coupling between the saltwater and freshwater zone by growing the relative role of diffusion and transverse dispersion, respectively. The interaction of the topography-driven forced and salinity driven free convection was investigated along a real hydrological section in Hungary. Simulation elucidated the fresh, brackish and saline character of the water sampled the different hydrostratigraphic units by revealing the connection between the topography-driven upper siliciclastic aquifer and the lower confined karstic aquifer through faults in high-salinity clayey aquitard. The current study improves the understanding of the interaction between the topography-driven forced and the salinity-driven free convection, i.e. topohaline convection, especially in basin-scale groundwater flow systems.
Causes and water sources of flowing artesian wells attracted the interest of many hydrogeologists throughout history, however, a quantitative model that satisfactorily considers the roles of topography, groundwater recharge/discharge and aquitards on hydraulics of flowing wells is still lacking. In this study, a three-layer river-valley basin with a recharge boundary is used to obtain the basinal flow field, spatial distribution and transient discharge rates of flowing wells. Even if there is an aquitard separating the unconfined and the confined aquifer, groundwater discharge to the river still plays a critical role in occurrence of flowing wells. An aquitard with lower permeability would enlarge the zone with flowing wells, implying that flowing wells are more likely to occur in basins with continuous aquitards. By comparing flowpaths and inter-aquifer leakages before and after numerically installing a flowing well in a three-layer basin, we find decreased upward leakage in the discharge limb plays a much larger role than increased downward leakage in the recharge limb in the stable discharge rate of a flowing well. This recognition is different from previous studies where the stable discharge rate is supported only by downward leakage from the overlying aquifer. By considering well hydraulics in a basinal background flow field, this study improves understanding of the mechanisms of flowing artesian wells and the interaction of surface water and deep groundwater, indicating that flowing wells are valuable for sampling deep groundwater representative of deep and old groundwater in the discharge area of a basin.
Study region Buda Thermal Karst system, Hungary. Study focus The pilot area has high geothermal potential characterized by prominent thermal anomalies, such as thermal springs and spas which tap the Triassic carbonate aquifers. Therefore, numerical simulations were carried out to examine the temperature field and flow pattern considering three successive heat transport mechanisms: thermal conduction, forced and mixed thermal convection in order to highlight the role of different driving forces of groundwater flow in the Buda Thermal Karst. New hydrological insights for the region Compared to thermal conduction, topography-driven heat advection increases the surface heat flux. The superimposed effect of free thermal convection facilitates the formation of time-dependent mixed thermal convection from the deep carbonate layers. The Nusselt number varied between Nu = 1.56 and 5.25, while the recharge rate (R) ranged from R = 178 mm/yr to 250 mm/yr. Radiogenic heat production and hydraulically conductive faults have only a minor influence on the basin-scale temperature field and flow pattern. Boundary conditions prescribed on the temperature and pressure can considerably affect the numerical results. In each scenario, independently of the model parameters, time-dependent mixed thermal convection evolved both in the deep and the confined parts of the karstified carbonates of the Buda Thermal Karst system.
Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.
Abstract: Assessment of the long term possibilities and risks related to geological storage requires insight in the deep groundwater flow systems. The objective of this paper is to show the relevance of the deep creep flow of the earth’s viscous upper mantle and crust as a complement to the groundwater flow. The paper presents an approach based on Fourier decomposition of the topography. The creep flow equations are solved analytically, which results in simple indices like penetration depth and relaxation time characterizing the gravity-driven creep flow. The very high viscosity of the Earth’s subsurface allows for a Darcy-like equation in which the ‘creep conductivity’ is Fourier mode dependent, which allows for simple comparison with the hydraulic conductivity for groundwater flow. Since creep conductivity is proportional to the square of the Fourier mode’s horizontal extension, creep velocities in the deep subsurface are significant with respect to deep groundwater velocities. Keywords: Creep Flow; Crust and upper mantle; Darcy’s law; Deep geological storage; Effective viscosity; Groundwater flow; Unsteady Stokes Equation
The control and management of seawater intrusion in coastal aquifers is a major challenge in the field of water resources management. Seawater intrusion is a major problem in the coastal aquifer of Wadi Ham, United Arab Emirates, caused by intensive groundwater abstraction from increased agricultural activities. This has caused the abandonment of salinized wells and ultimately affected farming activities and domestic water supply in the area. In this study, the 3D finite element groundwater flow and solute transport model is developed using FEFLOW to simulate pumping of brackish water from the intrusion zone to control seawater intrusion in the aquifer. The model was calibrated and validated with available records of groundwater levels and salinity distribution. Different simulation scenarios were conducted to obtain optimum pumping locations, rates as well as a number of wells. A comparison between scenarios of non-pumping and pumping of brackish water was conducted. Results showed an increase in the concentration of groundwater salinity under the non-pumping scenario, while it decreased under the pumping scenario. Under the non-pumping scenario, isoline 30,000 mgl⁻¹ was observed to have intruded into the south-eastern part of the aquifer, while the maximum isoline observed for the same area under the pumping scenario was 20,000 mgl⁻¹. This result showed an overall improvement in the quality of groundwater and ultimately halted seawater intrusion in the aquifer.
The dynamics of the underground part of the water cycle greatly influence the features and characteristics of the Earth's surface. Using Tóth's theory of groundwater flow systems, surface indicators in Mexico were analyzed to understand the systemic connection between groundwater and the geological framework, relief, soil, water bodies, vegetation, and climate. Recharge and discharge zones of regional groundwater flow systems were identified from evidence on the ground surface. A systematic hydrogeological analysis was made of regional surface indicators, published in official, freely accessible cartographic information at scales of 1:250,000 and 1:1,000,000. From this analysis, six maps of Mexico were generated, titled "Permanent water on the surface", "Groundwater depth", "Hydrogeological association of soils", "Hydrogeological association of vegetation and land use", "Hydrogeological association of topoforms", and "Superficial evidence of the presence of groundwater flow systems". Mexico's hydrogeological features were produced. The results show that 30% of Mexico is considered to be discharge zones of groundwater flow systems (regional, intermediate, and recharge). Natural recharge processes occur naturally in 57% of the country. This work is the first holistic analysis of groundwater in Mexico carried out at a national-regional scale using only the official information available to the public. These results can be used as the basis for more detailed studies on groundwater and its interaction with the environment, as well as for the development of integrative planning tools to ensure the sustainability of ecosystems and satisfy human needs.
Groundwater quality in the Central and Northern-Central volcanic terrain of Mexico has changed in the last two-three decades. Present abstraction regime has induced thermal (30-50º C) water with high, or low, mineral content. The quality of available water has trace (i.e. As) and minor (i.e. F-) elements in concentrations above drinking water standards, such trend is likely to continue unless an understanding of prevailing groundwater flow systems (intermediate and regional) is achieved. An analysis of data obtained in a step-drawdown-test coupled with temperature, pH and chemistry, provide an insight into the flow systems involved suggesting a water quality control with abstraction yield, and time. This test has the intention to provide bases for a method to define optimum abstraction yield including water quality and quantity aspects where the relevance of the groundwater flow systems is mandatory in any policy of groundwater extraction-quality administration.
The Villa de Reyes basin has is a fractured rhyolite structure with volcaniclastic sediments where groundwater is heavily extracted by competing water users (irrigation and a thermal-electric generating station). Groundwater levels currently drop at a rate exceeding 1 m/yr, its sustainability is a top priority. In this study, environmental isotopes were used to examine the age and sources of recharge to the deep groundwaters, to elucidate the relationship between deep and shallow groundwaters, and to find evidence for interbasin flow. Piezometric data show that gradients for both deep (to 400 m) and shallow (< 50 m) groundwaters in this semi-to unconfined aquifer are strongly controlled by the high topography of the surrounding volcanic highlands. Shallow groundwaters have highly variable stable isotope contents and are tritiated, indicating modern recharge by local infiltration. The deep groundwaters are well mixed and tritium-free, indicating long flow paths. Radiocarbon ages of the deep groundwaters are calculated with a process-oriented model calibrated with 14C data from modern groundwaters. Results suggest that deep groundwaters were recharged during the late Pleistocene to mid-Holocene epochs. Nonetheless, they are isotopically similar to the shallow groundwaters, implying similar recharge conditions. The long subsurface residence times for deep groundwaters, together with the piezometric evidence, do not preclude the possibility for interbasin flow, particularly under a hydraulic regime modified by pumping.
The start of most present cities was based on a good quality groundwater source, often discharge from local flow systems. As city growth advanced, the need for additional water was provided by digging shallow wells; presently, the need has been supported by additional and deeper wells. The resulting stress on the prevailing groundwater flow systems, initially on the relatively good quality local flows, has shown the natural response by the regional flows beneath. These flows travelling at depth with contrasting water quality to those of local nature, are affecting the water quality of existing wells, including those at shallow depth. An understanding of the presence of different flow systems at depth, mainly in cities where various km of rock formations having good aquifer characteristics prevail, the upcoming of regional flows should be given the correct consideration.
Often, regional groundwater research is meant to have some tens or a few hundreds of water samples for chemical and stable isotopes analyses. However, in remote arid areas as "Los Cirios" in Baja California Sur, Mex. it became a challenge to carry out such study due to the scarce general development. The regional flow systems theory allowed to have an acceptable hypothesis from available water samples (in springs and wells). The fresh and thermal water provided a sensitive relation with ecosystems through the three defined types of groundwater.
This study aims at recognizing the mechanisms of mass transport between the karst surface and the saturated zone in a morpho-structural relief of the Mesozoic karst carbonate platform of Murgia (Puglia, Southern Italy). The large dimension of the karst aquifer, the regional scale of the flow system, the boundary condition constituted by the sea, and the lack of freshwater springs constrain to the use of wells as monitoring points and limit the study area to the recharge area comprising 986 endorheic basins. The concentrations of non-reactive tracers (nitrates) in the waters of autogenic recharge (from endorheic basins) have been modelled through the evaluation of effective infiltration, land use, and nitrogen surplus, with reference to a time window, which includes a low precipitation period followed by significant rainfall events. The comparison between the modelled nitrate concentrations and the nitrate concentrations measured in ground waters, coupled with the analysis of groundwater chemograms and records of hydraulic heads (all referred to the same time window), allows inferring the mechanism of mass transport between the karst surface and the groundwater table. The mass transport conceptual model requires the presence of the epikarst. The infiltration of significant rainfall in the endorheic basins after a low precipitation period displaces waters stored in the epikarst towards the saturated zone. Ground waters in the post-evet period show higher concentrations of nitrates, lower concentrations of Total Organic Carbon and higher Mg/Ca ratios than both those of the pre-event period and the autumn-winter recharge period. The post-event recharge from epikarst storage determines a transient hazard of groundwater pollution with a time lag from the occurrence of the heavy rainfall.
The Nurra district in the Island of Sardinia (Italy) has a Palaeozoic basement and covers, consisting of Mesozoic carbonates, Cenozoic pyroclastic rocks and Quaternary, mainly clastic, sediments. The faulting and folding affecting the covers predominantly control the geomorphology. The morphology of the southern part is controlled by the Tertiary volcanic activity that generated a stack of pyroclastic flows. Geological structures and lithology exert the main control on recharge and groundwater circulation, as well as its availability and quality. The watershed divides do not fit the groundwater divide; the latter is conditioned by open folds and by faults. The Mesozoic folded carbonate sequences contain appreciable amounts of groundwater, particularly where structural lows are generated by synclines and normal faults. The regional groundwater flow has been defined. The investigated groundwater shows relatively high TDS and chloride concentrations which, along with other hydrogeochemical evidence, rules out sea-water intrusion as the cause of high salinity. The high chloride and sulphate concentrations can be related to deep hydrothermal circuits and to Triassic evaporites, respectively. The source water chemistry has been modified by various geochemical processes due to the groundwater–rock interaction, including ion exchange with hydrothermal minerals and clays, incongruent solution of dolomite, and sulphate reduction.
The flow system in fractured aquifers is complex to define. A reliable outline of flow system in such a type of aquifers can be obtained by using natural tracers: among them, temperature demonstrates very effective usuage. Convective thermal fields, resulting from convective disturbance on conductive thermal fields, can be reasonably interpreted like analogues of flow systems. A geostatistical approach by Ordinary Kriging has been applied to groundwater temperature data obtained from temperature logs performed in two fractured karstic and coastal aquifers (Murge and Salento) of Southern Italy. The variographic analysis shows the potential of the geostatistical approach in outlining regional and local scale anisotropies. Moreover, vertical and horizontal Ordinary Kriging temperature estimations at different depths allow recognizing main recharge areas and preferential flow-pathways.
Groundwater discharge can be an important determinant of the functioning of aquatic environments and their associated biological communities. However, the presence and the importance of groundwater have not been considered in the Parana River floodplain owing to the large quantity of surface water. The present study aimed to identify groundwater discharge conditions in a sector of the middle of the floodplain of the Parana River by studying groundwater flow systems. Eight piezometers were installed to record groundwater movement in the vertical plane weekly for 2 years. Water samples were collected in piezometers, domestic wells, the river and other water bodies to study the groundwater flow systems. Rising of the water level during piezometer installation and recording suggested that the study zone represents groundwater discharge conditions. Residence time proxy allowed identification of local flows and intermediate flows. Local rainfall (in Santa Fe) showed an isotopic signature (dD and d 18 O) similar to some local flows detected in the study zone, and this suggested local recharge. The chemical characteristics of an intermediate flow suggest that water would have travelled from a recharge area ~30 km from the study zone. Local rainfall and the intermediate flow have different isotopic signature. Results suggest that the willow forest is associated with the recharge area of a local flow, which plurispecific-canopy forest is related to a transit area of a semi-intermediate flow, and that tall grassland and marshy community colonize discharge areas of local and intermediate flows, respectively.
Groundwater flow systems have been differentiated in the metropolitan zone of Mexico City based on their chemical composition and stable isotope contents. The existing hydrogeological framework for the region provided a reference for such differentiation. Local flows (Flow-system I) represent the youngest and shallowest groundwater flow identified in boreholes on the hills. Intermediate flows (Flow-system II) in boreholes on the plain represent a mixture of inflows travelling horizontally, and vertically upwards (Flow-system IV) and downwards (overlaying aquitard leakage) to extraction boreholes. Flow-system III identified in boreholes on the plain is an intermediate flow system which extends deeper than Flow-system II. Flow-system IV, which is classified as a regional system, is related to a former thermal spring site. Groundwater travelling times, and their regional distribution and the thickness of related rock formations suggest extensive inflow supporting Flow-system IV. Future climate condition evolution (i.e. drought) will only have a limited impact on Flow-system IV as compared to Flow-system I which have relatively rapid and short flow paths. The identification of the hierarchy of the flow systems is of paramount importance in achieving adequate groundwater management in any region where the aquifer units are several thousand metres thick.
Heat and mass transport through porous media is governed by the advection-dispersion equation. Near the forward moving mixing front the longitudinal and transversal dispersion lengths are non-zero; only dispersion by molecular diffusion remains. The present paper presents mathematical-physical arguments why in steady transport the dispersion lengths are equal to zero. In conventional models the dispersion lengths are generally assumed to be process-independent. To interpolate between the relatively large dispersion lengths near time-dependent moving front and the steady transport conditions far away from the front, a mathematical model is proposed to describe the process-dependent time-evolution of the dispersion lengths. In this model, the dispersion lengths near the forward moving front are equal to the well-established conventional dispersion lengths that correctly represent the mixing near the front. However, further behind the moving front, where the mass transport has become (almost) steady, the process-dependent model results in vanishing dispersion lengths and, consequently, in a substantially smaller transversal mixing zone. Keywords: Advection, Flow systems, Mixing, Steady transport, Transversal dispersion
The groundwater divide within a plane has long been delineated as a water table ridge composed of the local top points of a water table. This definition has not been examined well for river basins. We developed a fundamental model of a two-dimensional unsaturated-saturated flow in a profile between two rivers. The exact groundwater divide can be identified from the boundary between two local flow systems and compared with the top of a water table. It is closer to the river of a higher water level than the top of a water table. The catchment area would be overestimated (up to ~50%) for a high river and underestimated (up to ~15%) for a low river by using the top of the water table. Furthermore, a pass-through flow from one river to another would be developed below two local flow systems when the groundwater divide is significantly close to a high river.
Gravity-driven groundwater flow systems function in topographic basins as subsurface conveyor belts. They pick up and move fluids, gases, solutes, colloids, particulate matter and heat from loading sites in recharge areas and/or on their way to the discharge areas and can deliver them "en route" or in discharge regions. Gravitational flow systems of various horizontal and vertical extents are organized into hierarchically nested complex patterns controlled by the configuration of the water table's relief and modified by the rock framework's heterogeneities of permeability. The systems are ubiquitous and act simultaneously on broad ranges of the spatial and temporal scales of measurement. Their universal geologic agency is manifest by numerous different, even disparate, natural processes and phenomena. Several of these are associated with geothermal heat flow. The understanding of geothermal phenomena in the context of basinal flow systems requires, therefore, an intimate familiarity with the overarching "Theory of regional groundwater flow" which, in turn, comprises two component theories: "The hydraulics of basin-scale groundwater flow systems" and "The geologic agency of basin-scale groundwater flow-systems". The paper's outline is based on this conceptual structure. The paper presents examples for geothermal effects of groundwater flow by means of the first theoretical models and some case studies of thermal springs and wells, and petroleum accumulations. The final section reflects the author's conviction that geothermal studies cannot be complete without consideration and understanding of the area's groundwater flow regime.
48 Mivel a vizsgált 1966-1985-ös idõszakban csak viszonylag rövidebb (egy-két éves) száraz periódusok voltak, feltétlenül indokolt volna a száraz években bõvel-kedõ 1986-1995 közötti idõszak lefolyási alapadatainak hasonló jellegû feldolgozása és értékelése is. Az 1995 utáni évek alapos vizsgálata ugyancsak megérné a fárad-ságot, mert ezek közt mindkét elõjelû szélsõség egyaránt elõfordul. Az alföldi lefolyás mérési adatokból meghatározott húszéves átlagát és a korábbi publikációinkban bemutatott tájegységenkénti értékeket az éghajlati adatokból szer-kesztett izometrikus lefolyási térképekkel (Lászlóffy 1954, 1967, 1982, MTA 1989) összehasonlítva megálla-píthatjuk, hogy a mért adatokból meghatározott lefolyások valamivel nagyobbak, aminek egyrészt a feldolgozási idõszak fent említett, az átlagosnál nedvesebb jellege lehet az oka, másrészt esetleg az, hogy ezek az értékek a természetes lefolyáson kívül a belvízrendszerekbe jutó különféle "idegen" vizek mennyiségét is tartalmazhatják, de az éghajlati adatokból szerkesztett lefolyási térképrõl leolvasható értékek sem teljesen megbízhatók.
The Takelsa multilayer aquifer system, located in north-eastern Tunisia, contains important groundwater resources that have mainly been used for agricultural purposes. To ensure a solid base for the sustainable management of this aquifer system, an adequate comprehensive hydrogeologic investigation was undertaken. A sampling campaign of stable isotopes was carried out in 2016 to identify groundwater recharge and related processes. A groundwater flow model was implemented. The model calibration was performed during a steady state, based on the average state of the period 1980–1984, using Modflow. Modelling results have been determined by a least squares fit of observed heads. The groundwater model was coupled with a physically based model (WetSpass model) used to quantify groundwater recharge and discharge of the Takelsa multilayer aquifer.
The theoretical examination of the combined effect of water table configuration and heat transfer is relevant to improve understanding of deep groundwater systems, not only in siliciclastic sedimentary basins, but also in fractured rocks or karstified carbonates. Numerical model calculations have been carried out to investigate the interaction of topography-driven forced and buoyancy-driven free thermal convection in a synthetic, two-dimensional model. Effects of numerous model parameters were systematically studied in order to examine their influence on the Darcy flux, the temperature and the hydraulic head field. It was established that higher geothermal gradients and greater model depths facilitate the evolution of time-dependent free thermal convection in agreement with changes of the thermal Rayleigh number and the modified Péclet number. However, increasing water table slope and anisotropy coefficient favor the formation of stationary forced thermal convection. Free thermal convection mainly affects the deeper part of the midline and the discharge zone of the synthetic model. In the examined model basins, the position of the maximum hydraulic head is located within the bottom thermal boundary layer near the recharge zone. This divergent stagnation point underlies a local downwelling zone characterized by underpressure. These simulations draw attention to the importance of understanding the combined effect of forced and free thermal convection in sedimentary basins regarding regional groundwater flow patterns, and temperature distributions.
During a regional hydrogeologic survey in the St. Lawrence Lowlands, Canada, a computer-based 3D Geologic Framework Model (GFM) was constructed to obtain a consistent representation of this typical Quaternary glaciated basin over a 1,400 km(2) area. Such a detailed stratigraphic reconstruction was needed because the Quaternary sediments control the recharge to the underlying regional fractured rock aquifer and also because buried granular aquifers are partly connected to the regional system. The objectives of this geomodeling effort are 1) to improve understanding of subsurface conditions above the regional aquifer and; 2) to provide a common stratigraphic framework for hydrogeologic applications. The method draws on knowledge-driven discrete modeling using gOcad, as well as standardization and quality control procedures to maximize the use of a multisource database. The resulting model represents the bedrock topography and the complex stratigraphic architecture of overlying sediments. The regional till aquitard, the marine clay aquiclude and the buried granular aquifers have been modeled with unprecedented details thus providing a well-constrained 3D hydrostratigraphic framework. The recharge zones of the rock aquifer represent about 35% of the study area. Buried granular aquifers are directly connected to the regional aquifer system over about 10% of the area. The model allows several applications such as assessing aquifer vulnerability and areal groundwater recharge rates; improving the GFM inter-operability with groundwater modeling systems would be the next logical step.
A regional hydrogeological study was carried out in the Maritimes provinces, in one of the main aquifer systems in Canada. The study area covers a land surface of 10,500km2, of which 9,400km2 is over Carboniferous and younger rocks. The sedimentary fractured bedrock is composed of a sequence of discontinuous strata of highly variable hydraulic properties, and is overlain by a thin layer of glacial till (mostly 4 to 8m). Depending on areas, 46 to 100% of the population relies on groundwater for water supply. Almost all residential wells are shallow (28m on average) open holes that are cased only through the surficial sediments. This paper describes a regional hydrogeological investigation based on targeted fieldwork, the integration of a wide variety of existing multisource datasets and groundwater flow numerical modelling. The aim of this paper is to present the current state of understanding of the aquifer system in a representative area of the Maritimes Basin, along with the methodology used to characterize and analyze its distinct behaviour at the regional, local and point scales. This regional hydrogeological system contains confined and unconfined zones, and its aquifer lenticular strata extend only a few kilometers. Preferential groundwater recharge occurs where sandy tills are present. The estimated mean annual recharge rate to the bedrock aquifers ranges between 130 and 165mm/year. Several geological formations of this Basin provide good aquifers, with hydraulic conductivity in the range of 5 × 10−6 to 10−4m/s. Based on numerical flow modelling, faults were interpreted to play a key role in the regional flow. Pumping test results revealed that the aquifers can locally be very heterogeneous and anisotropic, but behave similarly to porous media. Work performed at the local scale indicated that most water-producing fractures generally have a sub-horizontal dip along a north-east (45°) strike.
This paper reports on the characterization of hydraulic properties of regional rock aquifers carried out within a groundwater resources assessment project in the St. Lawrence Lowlands of south-western Quebec. To understand the aquifer behavior at both the fracture level and at field scale, hydraulic investigations were carried out using various aquifer tests. The groundwater flow at the local scale is controlled mostly by the fracture system. Results of the constant-head injection tests show a weak decreasing trend of hydraulic conductivity with depth indicating that a major part of the groundwater flow occurs in the first meters of the rock sequence. At the regional scale, the equivalent porous media approach is applicable. The hydraulic conductivity measurements were correlated to the scale of the aquifer tests expressed with the investigated aquifer volume. A simple interpolation procedure for the hydraulic conductivity field was developed based on the distance between field measurements and the tested aquifer volumes. The regional distribution of the hydraulic conductivity for the major fractured aquifer units indicates that dolostone is the most permeable whereas sandstone and crystalline rocks are the least permeable units.
This international symposium will examine the current state of the regional groundwater flow concept, discuss any recent theoretical advancement, and share experiences from applications spanning energy exploration to environmental management.
Despite the continuous increase in water supply from desalination plants in the Emirate of Abu Dhabi, groundwater remains the major source of fresh water satisfying domestic and agricultural demands. Groundwater has always been considered as a strategic water source towards groundwater security in the Emirate. Understanding the groundwater flow system, including identification of recharge and discharge areas, is a crucial step towards proper management of this precious source. One main tool to achieve such goal is a groundwater model development. As such, the main aim of this paper is to develop a regional groundwater flow model for the surficial aquifer in Abu Dhabi Emirate using MODFLOW. Up to our knowledge, this is the first regional numerical groundwater flow model for Abu Dhabi Emirate. After steady state and transient model calibration, several future scenarios of recharge and pumping are simulated. Results indicate that groundwater pumping remains several times higher than aquifer recharge from rainfall, which provides between 2 and 5% of total aquifer recharge. The largest contribution of recharge is due to subsurface inflow from the eastern Oman Mountains. While rainfall induced groundwater level fluctuation is absent in the western coastal region, it reaches a maximum of 0.5 m in the eastern part of the Emirate. In contrast, over the past decades, groundwater levels have declined annually by 0.5 m on average with local extremes spanning from 93 m of decline to 60 m of increase. Results also indicate that a further decrease in groundwater levels is expected in most of Emirate. At other few locations, upwelling of groundwater is expected due to a combination of reduced pumping and increased infiltration of water from nonconventional sources. Beyond results presented here, this regional groundwater model is expected to provide an effective tool to water resources managers in Abu Dhabi. It will help to accurately estimate sustainable extraction rates, assess groundwater availability, and identify pathways and velocity of groundwater flow as crucial information for identifying the best locations for artificial recharge.
Carbonate regions have great economic importance for water supply, oil and gas reservoirs, geothermal fluids and also Mississippi Valley-type ore deposits. Therefore, the understanding and consequences of flow pattern in carbonates require special interest. The hypogene and epigene karst areas of carbonate sequences were distinguished and associated with different orders of groundwater flow. However, the effect of confinement on flow pattern of carbonate aquifers was not fully considered in previous studies. We demonstrated the most important prerequisites and consequences of the application of the gravity-driven regional groundwater flow concept for carbonate sequences at different degrees of confinement. The results put into a frame the distribution of different springs and caves (epigene and hypogene) of the carbonate system of the Transdanubian Range, Hungary, and provide insights for better understanding of the hydrogeology of areas with similar unconfined and confined settings. Relationship among different flow regimes, distribution and character of springs and hypogene karstification processes, in addition to natural discharge-related phenomena, such as mineral and microbial precipitates, were recognized in the area of Buda Thermal Karst. This area is a natural laboratory where the connection between groundwater flow and karstification processes can be studied.
Application of the gravity-driven regional groundwater flow (GDRGF) concept to the hydrogeologically complex thick carbonate system of the Transdanubian Range (TR), Hungary, is justified based on the principle of hydraulic continuity. The GDRGF concept informs about basin hydraulics and groundwater as a geologic agent. It became obvious that the effect of heterogeneity and anisotropy on the flow pattern could be derived from hydraulic reactions of the aquifer system. The topography and heat as driving forces were examined by numerical simulations of flow and heat transport. Evaluation of groups of springs, in terms of related discharge phenomena and regional chloride distribution, reveals the dominance of topography-driven flow when considering flow and related chemical and temperature patterns. Moreover, heat accumulation beneath the confined part of the system also influences these patterns. The presence of cold, lukewarm and thermal springs and related wetlands, creeks, mineral precipitates, and epigenic and hypogenic caves validates the existence of GDRGF in the system. Vice versa, groups of springs reflect rock– water interaction and advective heat transport and inform about basin hydraulics. Based on these findings, a generalized conceptual GDRGF model is proposed for an unconfined and confined carbonate region. An interface was revealed close to the margin of the unconfined and confined carbonates, determined by the GDRGF and freshwater and basinal fluids involved. The application of this model provides a background to interpret manifestations of flowing groundwater in thick carbonates generally, including porosity enlargement and hydrocarbon and heat accumulation.
Groundwater flow, driven, controlled and determined by topography, geology and climate, is responsible for several natural surface manifestations and affected by anthropogenic processes. Therefore, flowing groundwater can be regarded as an environmental agent. Numerical simulation of groundwater flow could reveal the flow pattern and explain the observed features. In complex geologic framework, where the geologic-hydrogeologic knowledge is limited, the groundwater flow model could not be constructed based solely on borehole data, but geophysical information could aid the model building. The integrated model construction was presented via the case study of the Tihany Peninsula, Hungary, with the aims of understanding the background and occurrence of groundwater-related environmental phenomena, such as wetlands, surface water-groundwater interaction, slope instability, and revealing the potential effect of anthropogenic activity and climate change. The hydrogeologic model was prepared on the basis of the compiled archive geophysical database and the results of recently performed geophysical measurements complemented with geologic-hydrogeologic data. Derivation of different electrostratigraphic units, revealing fracturing and detecting tectonic elements was achieved by systematically combined electromagnetic geophysical methods. The deduced information can be used as model input for groundwater flow simulation concerning hydrostratigraphy, geometry and boundary conditions. The results of numerical modelling were interpreted on the basis of gravity-driven regional groundwater flow concept and validated by field mapping of groundwater-related phenomena. The 3D model clarified' the hydraulic behaviour of the formations, revealed the subsurface hydraulic connection between groundwater and wetlands and displayed the groundwater discharge pattern, as well. The position of wetlands, their vegetation type, discharge features and induced landslides were explained as environmental imprints of groundwater. The highly vulnerable wetlands and groundwater-dependent ecosystems have to be in the focus of water management and natural conservation policy.
Numerical simulations of coupled groundwater flow and heat transport are used to address how hydrogeological conditions can affect permafrost dynamics. The simulations are based on a two-dimensional vertical-plane conceptual model of a study site at the Iqaluit Airport, Nunavut, Canada, which includes a 50 m deep permafrost terrain with a shallow active layer, overlain by a paved taxiway with winter snow-covered embankments. Coupled groundwater flow and advective–conductive heat transport with freeze–thaw dynamics, temperature-dependent pore-water freezing functions, and latent heat are included in the model. The simulation results show that a smooth (low-slope) freezing function with a higher residual unfrozen moisture content produced a deeper thaw front compared to that using a steeper freezing function, generating a maximum increase in the depth to permafrost of 17.5 m after 268 years. Permafrost thaw rates in high-permeability zones within a heterogeneous system were also relatively higher compared to an otherwise equivalent homogeneous soil, resulting in a maximum increase of 2.6 m in the depth to permafrost after 238 years. As recharge water cools while flowing along the upgradient permafrost table, advectively driven heat transport is paradoxically shown to temporarily increase the height of the permafrost table in down-gradient areas.