The importance of information on the hydrological and geothermal situation with respect to the prospection of the new sources of low enthalpy water in Slovakia

Abstract

Slovakia is situated on the territory of West Carpathian Mts., representing a part of the young Alpine-Carpathian foldnappe system. Considering the small extension of Slovakia, about 49,000 km 2, one could say that the country is considerably rich in thermal water. Up till now about 60 localities with thermal water occurrences have been discovered, with a total yield of about 700 l/s. The yield of the separate localities fluctuates within 0.5–50 l/s and the temperature of natural springs within 20–70 °C. The thermal power obtainable from these waters may range up to about 60 million kcal/h ( Franko 1969 b). From the point of view of chemistry there are predominantly calcium-magnesium-sulphate-bicarbonate waters with mineralization usually within 0.5 ÷ 0.8 to 3.0, and in some places up to 4.0–6.0 g/l. The thermal waters are bound to the tectonic zone of the Inner West Carpathians, i. e. to its Mesozoic limestone-dolomite complexes. Mesozoic formations are on a row of parallel anticlinorii and synclinorii formed by Cretaceous folding. These anticlinorii and synclinorii follow approximately the direction of the Carpathian arch (SW-NE, W-E, NW-SE), being composed of a whole row of partial synclines and anticlines. The Cretaceous structural forms (morphotectonic units), i. e. mega-anticlines representing mountain-ranges, and megasynclines, representing Tertiary depression and lowlands are divergent according to their direction ( Mahel' 1966). The Cretaceous and post-Paleogene structural forms are deformed by the Neogene german-typical directional and transversal fault tectonics. The hydrogeological systems represent the result of the above three evolutionary tectonic stages. These systems include Cretaceous, post-Paleogene and Neogene forms, and determine the infiltration, accumulation and the spring areas, as well as the circuit, descent and ascent, of the thermal waters ( Franko 1969 a). The above mentioned lithological and tectonical situation caused the rise of thermal waters and presented the possibility of finding new sources of low enthalpy waters. Natural thermal springs occur in the fault on the border of depressions and lowlands. The temperature of the waters is mostly influenced by cold shallow subsurface waters in the spring area and in its close vicinity. For this reason the prospection of low enthalpy waters will be oriented into the deepest parts of depressions and lowlands with respect to the favourable structural situation. Another factor offering the possibilities of finding new sources of low enthalpy waters is represented by the favourable geothermal conditions ( Franko 1969 c). The average value of the heat flow is 2.13 μcal/cm 2 sec: the values move within 1.32–2.70. It is a higher value than the central-European 1.67 (Čermák 1968) and the world average 1.58 ( Lee, Uyeda 1965). Also the average value of the geothermal degree on territories including thermal water is higher than the world average 33 m/°C. The increased values of the flow indicate, that for the heating of a certain amount of cold water less extensive areas are necessary than those found by geothermal balance with the use of the values of the world or the central-European average. The decreased values of the geothermal degree indicate the possibilities for the drilling and finding of warmer waters than those with the temperature calculated for the same depth according to the world average values. Favourable hydrogeological structures and geothermal situation offer opportunities for finding new sources of low enthalpy waters in Slovakia.