Les traceurs en hydrogéologie karstique. Leur apport à la connaissance des réservoirs aquifères calcaires

How use of tracers in hydrogeological surveys can help to locate karst groundwater

¹ CNRS, Moulis
² CENG-SARR, Grenoble
³ BRGM, Paris

Abstract

Although tracers have been in use in karst hydrology surveys for a very long time, their full "data potential" does not seem to have been exploited, for it is now realized that they are capable of yielding a hitherto unsuspected wealth of information. Potholers are practically the only people to have used tracers for exploration of karst formations, in the course of which they have gradually improved their methods and equipment by addition of such "refinements" as "fluorescein monitors", multiple tracing methods, etc. From their data, relationships have been established between aquifer water loss and spring flow, catchment area boundaries and "diffluence effects" have been determined, and points of leakage from storage ponds have been located. Recent research findings on tracers and tracing methods have shown that it is possible to analyse actual tracer behaviour in the system between points of injection and re-emergence, in addition to tracer link problems as hitherto, though subject to study of the residence time distribution (a basic requirement for this type of analysis). From recent data on karst aquifers and their hydrodynamic properties, the residence time distribution emerges as an important factor for understanding the structure of karst formations. Water circulation patterns are known to differ considerably at high and low water conditions, and the existence of a drainage network interconnecting the storage sub-systems of a karst aquifer is also an established fact. And, it so happens that a major problem with this type of aquifer is to locate its drainage network and determine its role in the overall system. Thus, some kind of "catalogue" of residence time distributions for karst aquifers of known hydrodynamic characteristics would no doubt be useful both as a "working tool" and in reviving interest in the use of tracers for investigation of groundwater in karst formations.