Use of combined recession curves analyses of neighbouring karstic springs to reveal karstification degree of groundwater springing routes

Abstract

In the southern part of the Slovenský Kras Mts., positioned on the territory of Hungarian-Slovak transboundary karstic hydrogeological structure of Dolný vrch/Alsóhegy, several karstic springs occur. Hydrograph recession curves from nine gauged springs on the Slovak part of the transboundary aquifer were analyzed. Individual springs were classified by typical groundwater depletion hydrograph into categories by typical depletion equations. These were also assigned to the different lithostratigraphic limestone types occurring in the springing areas and assumed recharge areas. Previous hydrogeological mapping had first indicated a suspicion on the possible linking of groundwater from the two individual springs, to be only the two surface appearances of the same springing groundwater in the neighbouring springs. By coupling the outflowing volumes of the two springs together, and analyzing the resulting new time series, new classification of subregimes could be done. Surprising new facts were revealed about the analysed pairs of springs, which primarily were not recognized as connected branches of one spring. Summation of discharged volumes into one entity lead in two cases to discovery of apparent presence of turbulent flow subregimes on the recession curves. Two branches of one outflow from the recharge area exist there; one of them usually represents the lower branch with “baseflow” and another, the upper one, is the overflow spring. This also influences the aspects of groundwater-sensitivity-to-pollution, and also gives unexpected hopes for further speleological investigations nearby.