6 - Natural tracing in karst aquifers

This chapter discusses the natural tracing in karst aquifers. Porous and fissure aquifers show statistical homogeneity of their physical and hydraulic characteristics on a scale ranging from tens to several hundreds of meters. Their groundwater resources can actually be explored by a simple approach, i.e., defining the aquifer geometry from geological data, and determining local hydraulic parameters from pumping tests; finally, local data are generalized to the whole aquifer through regionalizing techniques. On the contrary, karst generating processes create a peculiar void heterogeneity; voids may reach several meters in diameter and several kilometers in length. These voids are organized in a hierarchized network from the surface to an often unique spring: This is the conduit or drainage network. In this context, karst hydrogeologists must adopt a different approach to characterize a karst aquifer, its resources, and storage, i.e., via an accurate description of the void organization and an analysis of its overall behavior and that of its different parts or “organs.” The existence of conduits and of large voids makes the karst medium very peculiar—it is the only aquifer that can be entered by means of natural ways and can be gone through.