Quantitative Approaches in Characterizing Karst Aquifers

Abstract

Karst aquifers are an important ground-water resource and are highly vulnerable to contamination due to relatively fast transport and limited attenuation processes. Quantitative understanding of karst hydrologic functions is integral to managing water resources and developing protection or remediation strategies. However, traditional methods of aquifer characterization and testing, based on Darcian approaches, provide misleading or inadequate quantitative data when applied to karst settings. This difficulty is partly a problem of scale (volume of aquifer tested), and partly a problem of the complex nature of the typical karst aquifer system. Early approaches to studying karst concentrated on describing geomorphic features and their hydrologic functions, or understanding singular elements of karst flow dynamics, such as spring discharge, or hydraulic properties of solutional conduits. However, proper understanding of karst aquifers requires a systems approach in which the hydrologic function of each primary component—vadose zone, epikarst, and conduit network—is considered separately and as an integrated part of the whole system. The major difficulty facing the hydrologist is that karst aquifers typically exhibit dual ground-water flow regimes, that is, fast (conduit-dominated) flow and slow (diffuse) flow. In selecting investigative techniques to characterize properties of a karst aquifer, it is therefore important to determine how the data obtained by a particular test method are influenced by the fast-flow regime, slow-flow regime, or both. With this point in mind, several quantitative methods that are particularly useful in investigating the hydraulic parameters of the karst aquifer system are briefly discussed here. Quantitative water-tracing tests, conducted with fluorescent dyes, are among the most useful types of field