Quantification of water flow in a karst massif

Karst areas are critical environments for groundwater, representing the source of drinking water for ca. 50% of the population in Austrian and about 25% of the population in Europe. Karst refers to complex, predominantly underground drainage systems and special land features that are created by the dissolution of rock (mostly limestone). In terms of groundwater flow inside the mountains, it is possible to distinguish the partially water-filled vadose zone and the completely water-filled phreatic zone below the water table. In the vadose zone, karst caves and shafts created by dissolution allow water to drain away quickly. This in turn makes the groundwater in the phreatic zone, which feeds the drinking water sources, vulnerable to contamination. Therefore, groundwater modelling and management requires a detailed understanding of the waterways as well as the storage of the water in the rocks and caves. Karst caves allow direct access and thus measurements in the vadose zone. In this study, we focus on the Hochschwab karst massif where more than 1000 mainly shaft-like caves are known. The area is of particular importance as it is the water supply of the cities of Vienna and Graz and. In recent decades, numerous studies have been carried out in this area dealing with rock formation and structures, water conditions as well as caves and karst features, which form a good basis for this project. However, none of those studies have addressed geophysical monitoring. To study water flow and storage in the vadose zone, as well as groundwater recharge and storage in the karst system, we will use different geophysical methods, which permit to monitor changes in groundwater properties in a non-invasive manner and the possibility to investigate areas not accessible with common hydrological sensors. Geophysical results are supported through measuring stations located at cave streams that can provide direct information, for instance how quickly they react to rain events. The application of different methods should lead to a joint analysis of the data as well as to an interdisciplinary evaluation of the results. The aim of the project is to find a connection between the fracture surfaces in the rock and the surface and underground karst forms with the flow or storage properties of the water. For the implementation, a close interdisciplinary cooperation between the Karst and Caves Group at the Natural History Museum Vienna and the Department of Geodesy and Geoinformation at the TU Wien, in particular the Research unit of Geophysics. The outcome of the project will be discussed with other groups dealing with groundwater management and modelling as well.