Geophysical survey of near-surface aquifers for the goals of Managed Aquifer Recharge in a settlement of the Danube-Tisza Interfluve, Hungary

For recent decades, the groundwater level has been decreasing in the area of the Danube-Tisza Interfluve, Hungary, mainly due to climate change. The average depth of water table is between 5-7 m in the elevated Interfluve area. The shallow eolian and fluvial aquifers of the region can be used to store water between the surface and water table for later extraction or for ecological benefit. Therefore, Managed Aquifer Recharge (MAR) systems could play an essential role in improving the stored water and the water balance in the Danube-Tisza Interfluve.

The aim of the research was to carry out a geophysical survey and a complex data processing in order to analyse the characteristics of near-surface sediments of Kerekegyháza town (Danube-Tisza Interfluve, Hungary) for MAR implementation. For a detailed understanding of the shallow geological environment in Kerekegyháza, we used three main data systems and previous interpretations. Stratigraphic information was collected and examined from (1) hydrogeological reports. In addition, (2) archived vertical electric sounding (VES) measurements were reprocessed. Furthermore, (3) two-dimensional electric resistivity tomography (ERT) was performed. Summarizing the lithological and electric resistivity data, 4 geological sections and a complex 3D data system were compiled.

Interpreting the preliminary information, a simplified three-layered (uncovered aquifer – aquitard – covered aquifer) geological model was set up in the pilot area. Based on the stratigraphic information and the electric resistivity values, the geological setting is more heterogeneous than the simplified model. Hence the determined layers are not horizontally continuous, except for the uncovered dry sand or quicksand aquifer with 0-3 m thickness. Below that, presumably clay lenses cause rapid lateral variations in the grain size and the resistivity. However, the correspondence between the electrical and lithological divisions is not evident due to the different resolutions of the applied methods. The ERT results suggest that the pattern of heterogeneity shows spatial variation, which requires further research to explain the exact geological causes. The most significant reservoir in the area of the town is the covered sand formation with ~15 m thickness, detected by all applied methods.

The results can provide background for planning the appropriate technique of Managed Aquifer Recharge in the town of Kerekegyháza, mitigating further groundwater subsidence. In addition, its application for further cities in the elevated region of the Danube-Tisza Interfluve can contribute to more sustainable management with available water resources.

The research was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014 project.