Conceptualization and implementation of a groundwater flow model for the Buda thermal-karst system, Hungary

Abstract

The purpose of this work was to characterize the flow system of the area by constructing a 3D steady-state model, which is able to describe the zone budget and potential levels of the flow system, and also be able to manage the different hydrostratigraphic units within different geologic zones. In this study hydrogeologic and hydraulics data of more than 100 observation and abstraction wells and springs, recorded over decades, were used and the first calibration results are presented. The VISUAL MODFLOW PRO software was applied to simulate the model.Key words: conceptual model, digital model, karst system, thermal water, zone budget IntroductionBudapest, the capital of Hungary, with its historically known thermal waters (ranging form 20 to 77 °C), plays an important role in the economy of the country. The existence of thermal water depends not only on the high geothermal gradient (1.5 times the global average), but also on the large thickness of karstic and porous aquifers. These aquifers form the hydraulically horizontally and vertically unified system connected to the cold water-bearing formations in the recharge area, which is proven by hydraulic, water geochemistry, isotopic, and geothermal data (Mádai 1927;Horusitzky 1938;Papp 1940;Kunszt 1947;Schulhof 1957;Alföldi et al. 1968Alföldi et al. , 1979Alföldi et al. , 1982Lorberer 2002;Deák 1978). Overexploitation connected to coal mining from the 1960s to the 1980s caused a considerable drawdown in the karst system (Alföldi et al. 1980;Liebe and Székely 1980;Böcker 1981 Geology, Vol. 56/4, 359-380 (2013) DOI: 10.1556/CEuGeol.56.2013 Conceptualization and implementation of a groundwater flow model for the Buda thermal-karst system, Hungary Zahra Poyanmehr Department of Physical and Applied Geology, Eötvös Loránd University, BudapestAlföldi and Kapolyi 2007). Decrease of pressure and water levels resulted in changes in geochemical quality and quantity of thermal springs. With this background the need to study the thermal-karst system increased, in order to avoid increasing environmental threats in the future. The current study uses the results of considerable geologic and hydrogeologic data to construct a 3D steady-state digital model of the flow system. The previous 2D or 3D models of the area (Heinemann and Szilágyi 1977;Csepregi 2007) deal with evaluating the infiltration and the effect of overexploitation connected to coal mining; to achieve these goals a one, or at times two-layered model, was sufficient. The current model deals with different hydrostratigraphic units within different geologic zones, which contributes to a better assessment of flow systems. In addition it is able to answer the appropriate questions concerning the effect of favorably or unfavorably-filled intervention; however, it is not yet able to carry out their impact assessment.

Budai karsztrendszer utánpótlódási viszonyainak hidrodinamikai vizsgálata vizgeokémiai adatok figyelembevételével

“…A számítások megegyeznek azzal a vízszint-értékkel, amely akkor állna elő, ha az adott termálkútban a víz a felszíni részeknél, a hozzá társítható forrás hőmérsékletéig hűlne le. Így a meleg-ágak térségében található termál-kutakra számított meleg-ági potenciál értékek alapján tisztáztam a terület modellezése szempontjából fontos áramlási pályákat (Poyanmehr Z., Toth Gy., 2010;Poyanmehr Z. 2013).…”