Improving accuracy and efficiency in discrete-continuum karst models

Discrete-continuum or hybrid models couple one-dimensional conduit flow with the surrounding three-dimensional flow in the fractured rock matrix. The applicability of these models to real karst aquifers is somewhat limited not only because they require detailed information about the conduit network, but also these models typically require considerable computational efforts. Moreover, in some models the simulated conduit-matrix exchange fluxes critically depend on a lumped exchange parameter and as such the accuracy of discrete-continuum models can be questionable. This study presents some ideas to improve the accuracy and efficiency of discrete-continuum models. It is shown that a well-index should be used instead of a lumped exchange parameter. It is also illustrated that local grid refinement around the conduits as well as parallel solvers based on domain decomposition can be useful to increase the computational efficiency of discrete-continuum models.