Abstract
Position, width and fragmentation level of fracture zones and position, sig-nificance and characteristic distance of fractures were aimed to determine in a carbonate aquifer. These are fundamental parameters, e.g. in hydrogeological modelling of aquifers, due to their role in subsurface water movements. The description of small scale fracture systems is however a challenging task. In the test area (Kádárta, Bakony Mts, Hungary), two methods proved to be applicable to get reasonable information about the fractures: Electrical Resistivity Tomography (ERT) and Pricking-Probe (PriP). PriP is a simple mechanical tool which has been successfully applied in archaeological investigations. ERT results demonstrated its applicability in this small scale fracture study. PriP proved to be a good verification tool both for fracture zone mapping and detecting fractures, but in certain areas, it produced different results than the ERT. The applicability of this method has therefore to be tested yet, although its problems most probably origin from human activity which reorganises the near-surface debris distribution. In the test site, both methods displayed fracture zones including a very characteristic one and a number of individual fractures and determined their characteristic distance and significance. Both methods prove to be able to produce hydrogeologically important parameters even individually, but their simultaneous application is recommended to decrease the possible discrepancies.
Highlights
35% of the land surface in Europe is covered by karst according to Karst in Europe COST 65 [1] and 25% of the global population is supplied by drinking water from karst aquifers [2]
Other smaller resistivity green areas which reach close to the surface (~50 Ω∙m at 12 - 20 m and 24 - 29 m) show that these areas are fractured at a very shallow depth and saturated with water originating from rain fallen just before the measurements were undertaken
Electrical Resistivity Tomography (ERT) produces information from greater depths supporting the interpretation of near-surface characteristics and the geology of the area, it can detect fractures, especially if the measurements are carried out following a rainy period and the distance between the fractures is large, in comparison with their depth
Summary
35% of the land surface in Europe is covered by karst according to Karst in Europe COST 65 [1] and 25% of the global population is supplied by drinking water from karst aquifers [2] These facts underline the importance of studying karst systems. The conceptual model produced by [7] and [8] provides a quantitative characterisation of karst and fractured systems In this model, the spatial frequency of karst conduits is one of the crucial parameters influencing the hydraulic functioning of a karst or fractured system. Geotechnical tools would be perfect for fracture mapping, but they provide only point-like information These methods are expensive and their application is strongly limited by field conditions, such as topography, artificial constructions, landslide risk or vegetation, which make the access to the study area difficult or even impossible. The Pressure-Probe method [23] which is a simplified version of the geotechnical instruments and which avoids all their aforementioned deficiencies may be an economic solution for such problems
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