# Innovative Hydrogeophysical Approaches as Aids to Assess Hungarian Groundwater Bodies
## 1 Introduction  
The protection and sustainable use of water resources are core provisions of the European Union legislation [1]. The Water Framework Directive--setting the background for all other water-related directives--requires member states to assess the qualitative and quantitative status of all water bodies and to ensure the protection or restoration of their good chemical and ecological state. The recently adopted second National Watershed Management Plan [2] defines four cornerstones for future actions: avoiding the global water crisis, preserving our water resources, using their potential efficiently and safeguarding ourselves from water hazards. The key instrument towards these goals is integrated water resources management [3]. However, effective actions require a sound basis of knowledge and information. In 2016, the Hungarian Academy of Sciences launched the National Water Research Program [4] to provide the scientific evidence base for implementing the strategic targets of the National Water Strategy. This baseline document provides a concise overview of the situation, based predominantly on the extensive documentation developed as part of the revision process of the Hungarian River Basin Management Plan by the National Water Directorate under the Ministry of Interior. One hundred eighty-five different groundwaterbodies were identified in the Hungarian River Basin Management Plan. The main goal is to achieve good quantitative and chemical status in the case of all groundwater bodies. Although this main objective seems to be quite simple, the whole work process needs much work from different experts. In this paper, it is demonstrated how different innovative hydrogeophysical approaches can be used effectively in this complex work to assess the Hungarian groundwater bodies. Table 1 summarizes 6 main challenges, which can be addressed by hydrogeophysical methods studied in this paper. To handle the above challenges, a good alternative is the application of both surface geophysical and borehole logging methods. Surface geophysical methods can give an overview of large areas in a relatively short time for acceptable costs. They are also applicable to characterize smaller areas with greater accuracy. Well-logging methods, including lithology (natural gamma-ray intensity, spontaneous potential), porosity (density, neutron-porosity) and resistivity logs in contrary give information only to selected points of an area, but they can describe very detailed the vertical variations of, e.g., lithology and shaliness, porosity and water-saturation which are basic in situ parameters in hydrogeological studies. Hydrogeophysical methods have been widely used recently to investigate water-bearing formations and handle challenging problems in preserving groundwater resources [5]. Among many other efficient investigation techniques, geophysical surveying methods are easy to implement and relatively inexpensive, of course, taking into account its limitations, which generally apply to research depth and spatial resolution as well as the problem of ambiguity that may occur during the interpretation of surface geophysical data. To improve the evaluation of groundwater formations, we suggest using some innovative geophysical methods. In problems related to groundwater, the relatively cost-effective electromagnetic [6; 7; 8] and direct current (DC) geoelectric methods [9; 10] are the most convenient tools. In addition to that, these methods can well separate lithological units; they are sensitive to the presence and quantity of subsurface water. Geological features, such as, e.g., faults, fractures, caves, which have a great influence on groundwater movements, are also detectable by these methods. While in large-scale studies, particularly very-low-frequency (VLF), e.g., in [11], and radio-magnetotelluric (RMT) methods are used [12], the geoelectric method is applicable both in large-, and small-scale studies.