Modeling of Karst Aquifers

Abstract

Groundwater flow through a karst aquifer is prone to contamination because of the very nature of the karstified host rock: Fissures and bedding partings in the rock are enlarged by chemical dissolution over time and provide preferential flow paths, through which water is transferred rapidly and almost unfiltered from input points such as sinks and dolines to output points such as large karst springs. The enlarged fractures and bedding partings are responsible for a very heterogeneous distribution of permeability within the karst aquifer. Enlarged passages can be very conductive (1–10 m s −1 ) but have low storage capacity. The surrounding rock is orders of magnitude less conductive (10 −8 m s −1 ), but can provide significant storage. This large-scale heterogeneity in conductivity makes it difficult to assess the karst aquifer properties from field studies such as borehole pumping, packer, and slug tests. Monitoring spring discharge, on the other hand, provides only an integral picture of the karst aquifer. A different approach to understanding a karst aquifer and its spatial and temporal evolution are numerical models. This field has evolved dramatically over the last decades, and is described in this article.