ABSTRACT
A method that sets karst hydrogeology apart from those methods practiced in other terrains is that a part of the groundwater flowpaths – the larger conduits – can sometimes be directly explored and mapped by speleologists. In combination with water tracing, this can be useful to get a more complete overview of the locations of underground flows and to determine key sites for the collection of water samples, either directly or through the placement of monitoring wells. For example, direct mapping of caves can identify underground stream confluence locations that can only be approximated through tracing, which can allow for sampling that represents entire sub-groundwater catchments. For example, in Slovenia, the confluence of the Pivka and Rak underground rivers has been found in Planinska Jama. Both rivers have huge and independent catchment areas, one being mainly allogenic (derived largely from surface drainage from Flysch deposits) and the other being mainly autogenic (derived from precipitation directly onto a limestone surface). In Milandre Cave (Jura, Switzerland) three main tributaries feed the underground river. Their respective catchments have been delineated quite precisely with the aid of more than a hundred tracing experiments. Access to the cave made it possible to sample each tributary separately (Fig. 3.1). Within Mammoth Cave (Kentucky, USA), discovery and mapping of the confluence of the Logsdon and Hawkins Rivers deep in the cave system allowed the placement of monitoring wells 100 m upstream from the junction, allowing easy sampling of their 25 km2 and 75 km2 catchment areas, respectively. This was especially important to understand agricultural impacts on groundwater quality in this cave, which has been designated not only as a US National Park, but also by UNESCO as an International Biosphere Reserve and World Heritage Site (see also chapter 4).
