Fold structure and underground drainage pattern in the alpine karst system Hochifen-Gottesacker

Abstract.: This paper summarises seven years of hydrogeological research in the alpine karst system Hochifen-Gottesacker (Germany/Austria). Geologically, the site belongs to the Helvetic nappes and consists of Cretaceous sedimentary rocks. The Schrattenkalk limestone forms a relatively thin karst aquifer above or between thick marl aquicludes, forcing groundwater to flow parallel to the strata. The limestone is intensively cut by faults and fractures favouring karstification. The fault offsets are relatively small, so that their influence on the large-scale groundwater flow paths is limited. The site is thus ideal to study the influence of fold structures on the drainage pattern. Multi-tracer tests with a total of 16 injections demonstrated that troughs of plunging synclines form the main underground flow paths, while crests of anticlines act as local groundwater divides in the higher karst zones where the base of the aquifer is above the level of the surrounding valleys. In an adjacent valley that receives inflow from several synclines, tracer tests confirmed a major underground drainage system running across the folds. An axial culmination in the area is part of the continental water divide Rhine-Danube; an axial depression acts as a zone of confluenc