Modeling of karst aquifers

Abstract Flow in karst systems can occur in at least three modes: matrix, fracture, and conduits. Matrix flow, or flow in the (primary) intergranular pore space, is laminar and generally accepted to be well described by Darcy's equation. Laminar flow through secondary openings (joints, fissures, faults, and bedding plane partings) also occurs in many carbonate aquifers. Secondary and matrix flows are frequently lumped together, characterized as diffuse flow, and represented using Darcy's equation. Conduit flow occurs through larger pathways, such as open conduits, and may be laminar or turbulent, depending on the conditions. Karst aquifers can be modeled using response function approaches, lumped parameter models, and distributed parameter models. Response-function and lumped-parameter or reservoir models are generally limited to the predictions of spring flows, but can be useful when data are sparse and when the system output can be correlated with input. It is advisable to limit the use of these models to the range of conditions and stages over which the correlations were established. Distributed parameter models can be classified as embedded discrete-conduit models; single-continuum, smeared-conduit models; and dual-continuum models. Current state-of-the-science karst modeling approaches employ distributed parameters and have the ability to simulate laminar flow in the matrix and both laminar and turbulent flow in the conduits under fully saturated and partially saturated hydraulic conditions.