Karst hydrogeological investigations in Salzburg, Austria

The mountains in the province of Salzburg consist to a large extent of rocks prone to karstification. Between 1967 and 1981, several tracer tests have been carried out in order to determine residence times and catchment areas of springs. Since 2007 these karst areas have been investigated using more modern methods. Five areas (Untersberg, Hagengebirge, Tennengebirge, Leoganger Steinberge and Kitzsteinhorn) are presented here. Beneath the Untersberg, a central underground lake with a surface around 10,000 m² extends over 3 km. Its lake level fluctuates by around 50 m. Previously assumed connections between the karst groundwater and the porous aquifers in the surrounding valleys can be excluded. In Hagengebirge, karst head fluctuations exceeding 220 m have been documented instrumentally. The most important spring has low mineralization in the dry season and during high discharge periods. With a rising water table, sulfate-bearing evaporite rock masses with lower permeability become flooded which mineralizes the karst groundwater. Water mineralization increases significantly only during periods of decreasing discharge after rain events or snow melt. Head fluctuations in Tennengebirge vary locally between 5 and 75 m. Continuous monitoring revealed a lifter system in the Leoganger Steinberge during a flood event, as well as the influence of a nearby hydropower plant on runoff, temperature and electric conductivity of the Kesselfall springs.