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This study examines the patterns of groundwater flow and salinity in a region of confined basement carbonate aquifer along with the region's unconfined adjacent part and siliciclastic confining strata. An understanding of regional-scale flow patterns in this setting may prompt a rethinking of the traditional view. According to that view confined carbonates are bounded and isolated by impermeable confining layers from their surroundings. A basin-scale analysis of the subsurface conditions promises better to accentuate otherwise unseen signs of hydraulic communication both horizontally and vertically between different parts of the flow domain. This study reveals that various flow regimes exist, in the area of the Paleogene Basin, Hungary. The pattern and intensity of these flow regimes depend on the elevation of basement carbonates and the structures, thickness, hydraulic conductivity and heterogeneity of the covering layers. Effects of gravity-driven regional groundwater flow were identified down to an elevation of −500 m asl including recharge and discharge areas. Hydraulic communication occurs both vertically and laterally in this zone but the direction and intensity of flow are influenced by aquitards or confining layers. Nevertheless, hydraulic boundaries (a colinear ridge in the north and a sink in the south) were recognized in the study area. This impedes horizontal hydraulic communication between the shallower unconfined-to confined carbonates in the west and the deeper confined carbonates in the east. Southeasterly through-flow can be observed below −500 m asl elevation which terminates in a regionally underpressured zone due to a regional aquitard in the zone of uplift. Both underpressured and overpressured blocks bounded by faults appear to influence vertical connections between siliciclastic confining layers and carbonates in the vicinity of significant strike-slip faults. The flow regimes thus recognized affect the subsurface salinity pattern, and hydrocarbon migration and as a result the planning of geothermal exploration. Consequently, a priori assumption of impermeability of confining layers and hydraulically isolated carbonate compartments below seems to be an oversimplification.

The Buda Thermal Karst area, in central Hungary, is in the focus of research interest because of its thermal water resources and the on-going hypogenic karstification processes at the boundary of unconfined and confined carbonates. Understanding of the discharge phenomena and the karstification processes requires clarification of the groundwater flow conditions in the area. Accordingly, the aim of the present study was to present a hydraulic evaluation of the flow systems based on analyses of the archival measured hydraulic data of wells. Pressure vs. elevation profiles, tomographic fluid-potential maps and hydraulic cross sections were constructed, based on the data distribution. As a result, gravitational flow systems, hydraulic continuity, and the modifying effects of aquitard units and faults were identified in the karst area. The location of natural discharge areas could be explained and the hydraulic behavior of the Northeastern Margin Fault of the Buda Hills could be determined. The flow pattern determines the differences in the discharge distribution (one- and two-component) and related cave-forming processes between the Central System (Rozsadomb area) and Southern System (Gellert Hill area) natural discharge areas. Among the premises of hypogenic karstification, regional upward flow conditions were confirmed along the main discharge zone of the River Danube.

Summary 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.

The paper proposes the involvement of preliminary regional hydrodynamic analysis for the reconnaisance phase water-based geothermal exploration in sedimentary basins. This approach is based on basin-scale pore pressure evaluation, it complements the usual reservoir and temperature analyses. Understanding of subsurface pore pressure distribution is beneficial not only in planning thermal water production but also in reinjection. The method is demonstrated for a sedimentary basin characterized by overpressured and superimposed gravity-driven flow. The key point of the approach is the understanding of regional pressure regimes and the delineation of the boundary of overpressured and gravitational flow domains.

The Duna-Tisza Interfluve, Hungary, is characterized by patchy surface salinization. However, in the Duna Valley, salinized wetlands appear in a N–S trending continuous zone (Lake Kelemenszek area). The source of the salts is reported to be the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. This “basement and basin origin of salts” concept is based on the strong correlation between the regional distribution of surface salinization and the basinal flow pattern. This study, applying integrated methods, presents hydrogeological evidence for this theory and creates a conceptual model for the salinization. The model reflects that the basement water rises near to the surface through conductive faults crosscutting an extensive aquitard and aquifer. These faults ensure “shortcut”-type water exchange between the basement and the uppermost aquifer. This hydraulic setting generates chemical anomalies in this aquifer up to the surface, producing Na–HCO3–Cl-type water. This water causes extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. Where a freshwater lens is located above the ascending saline water, this fresh gravity-driven flow controls the surface distribution of salts, which results in saline patches.

In the Danube Valley, a chain of saline lakes and a salinized area are situated in the discharge zone of two different waters. The two watertype were followed till the near surface by regional chemical and hydraulic investigations (Madlne Szőnyi and Toth 2009). The goals of this study were to prove the presence of these different waters in the near surface zone around the Lake Kelemenszek, and allocate their connection to the lake and to the salinized ground surface. Near-surface geophysical measurements (VES, RMT) supported the regional hydraulic and chemical results. The sediments are saturated by saline water down to 110 m beneath the lake, and to the east the fresh water is prevalent. The local chemical investigations strengthened this distribution. Highly saline water with Na-HCO3-Cl-type discharges into and around the lake. To the east there is a continuous change towards a (Ca,Mg)-(HCO3)2-type fresh water discharge. The interface between the two water types is a 2–3 km wide transition zone...

The paper introduces the method of regional hydrodynamic analysis based on pore pressure evaluation into the preliminary geothermal evaluation, in sedimentary basins influenced by overpressured and superimposed gravity-driven flow. This novel approach complements the usual reservoir and temperature analysis. Understanding of subsurface pore pressure distribution is also beneficial during planning of thermal water reinjection. The approach is demonstrated for the Duna-Tisza Interfluve of the Pannonian basin and the results are compared with operational experiences. The results can give basis for numerical modeling and provide background for aligned utilization of drinking water, thermal water and hydrocarbons in sedimentary basins.

In addition to geological conditions, hydrocarbon migration and entrapment is highly influenced by regional groundwater flow based on hydraulic theory of hydrocarbon migration. As a consequence, hydrogeological flow analysis contributes to petroleum exploration. The case study is represented from the Pannonian Basin, characterized by a complex groundwater flow situation, with an overpressured flow regime overlain by a gravity-driven flow system. In this situation the hydrocarbon migration is controlled by the way of overpressure dissipation, while hydrodynamic constraints influence the entrapment. The hydrocarbon migration can hydrodynamically occur up to the boundary of downward gravity-driven flow and upward flow of the overpressured system. Based on the study, these are contolled by the hydraulic function of fault zones and low-permeability formations. These findings were verified on three study areas with hydrochemical and temperature data as well.

The exploitation of geothemal energy in sedimentary basins requires detailed investigation of the geothermal and fluid flow field and the reservoirs of an area. Usually, geothermal evaluations are constrained to reservior scale. Investigations are carried out regarding the available heat and fluid, and the reservoir properties. However, in hydraulically continuous sedimentary basins the reservoir can not be handled as an individual entity. To resolve this problem, the term „reservoir” has to be extended to „basin scale” to understand processes and fluid-based geothermal possibilities in a sedimentary basin. The regional hydrodynamic evaluation give a framework and complements the traditional reservoir scale analysis. The findings are demonstrated for the Pannonian Basin, Hungary.

The estimation of evaporation and water budget of inland water surfaces are important for better understanding of interrelationship between the surface water bodies and groundwater flow systems. The aim of our study was to determine the water budget of a shallow (40–60 cm deep) lake and to allocate the origin of the high salt content of the lake water using micrometeorological measurements. The subject of our study is Lake Kelemen-szek (Hungary), located in the discharge area of a gravity-driven and an over-pressured hydraulic system. The micrometeorological measuring tower was installed 40 m offshore in the lake. The continuous and simultaneous measurements of global and net radiation, temperature, relative humidity and wind speed gradients, wind direction, precipitation, and determination of water temperature profile started in August 2006. The diurnal and monthly variations of evaporation were determined using three different methods based on micrometeorological measurements: (i) the energy budget, (ii) the Bowen ratio and (iii) the profile method. The results obtained through different methodologies were compared.