# Innovative Hydrogeophysical Approaches as Aids to Assess Hungarian Groundwater Bodies
## 2 Materials and Methods  
### Conditions and the Relevant Situations of the Hungarian Groundwater Bodies  
Groundwater resources play a major role in Hungary's drinking water supply system [34]. More than 95% of our drinking water is provided from groundwater resources; meanwhile, Hungary is famous for its mineral, therapeutic, and thermal water supplies. Hydrogeologists have high professional responsibility to safeguard our groundwater resources and manage their sustainable utilization in quantitative and qualitative terms [35]. During the past years, hydrogeologist experts had to face numerous global or local environmental and social threats that have significant adverse effects on the environmental elements, especially on groundwater [36]. Hungary is located on the Danube watershed in the Carpathian Basin, which is one of the most closed basins of the world concerning the water budget. This geographical feature has especially important effects on surface waters and our groundwater resources. The River Basin Management plan of Hungary contains 185 groundwater bodies, out of which 40 are officially registered as transboundary aquifers; however, the actual dependency is even higher. Approximately 50% of the groundwater bodies are divided by the national border; thus, external effects also influence the quantity and quality of our groundwater resources. As valuable kinds of these groundwater bodies, thermal and thermal karstic water bodies and their designated boundaries are shown in Figure 1. These karst groundwater bodies, with their special fracture systems, are very sensitive to the effects of climate change or to the different surface contaminations. Hungary shows a rather diverse geological and hydrogeological scene, where almost every unique and challenging feature can be observed in close vicinity to each other [37]. In addition to the hydrogeological features of our karstic mountains (that have a significant role in the drinking water supply), one can study the rather interesting water-bearing parameters of fractured volcanic, plutonic and metamorphic rocks. The Great Plain, which  
Figure 1: Twenty-nine Hungarian karst and thermal karst groundwater bodies were identified by the Hungarian River Basin Management Plan. attracts international attention, and the Small Plain (Kisalfold) geographical units provide several problems to be solved by hydrogeologist experts. Among others, the reason for the unique natural variations is due to the relative thinness of the Earth's crust under the Pannonian Basin and due to the even recently observed tectonic compression causing increasing pore pressure of deeper reservoirs and fluid containing strata of the basin. To interpret the reconstructed subsurface flow pattern of the Great Plain, one must divide the role of two driving energy sources. A gravity-driven flow system is found at shallow depth, and underneath, there is a pressurized flow system controlled by the tectonic compression [38]. The anticlines of the pre-Neogene Basin are the source areas of these highly pressurized regions. The pressure conditions are driven by sedimentation, raising the fluid temperature and tectonic compression. The vertical flow component shows uniformly upward in these deep, over-pressurized hydraulic flow systems. The contact zone of the two mentioned flow systems is very complex, and its depth is still unknown at certain points of the Great Plain. The shape and dynamic feature of the interaction zone varies significantly depending on the local topographical, meteorological and geological conditions. The geological matrix of the Great Plain consists of a complex, at some points 7000 m thick Neogene sediment overburden above the pre-Neogene basin. The porous structures in Hungary contain approximately 5000 km\({}^{3}\) of water at a given time. This volume is the so-called static groundwater resource. Dynamic groundwater resources play a more important role in sustainable groundwater utilization; its estimated volume is approximately 2-3 km\({}^{3}\)/year [3].