Computational Fluid Dynamics Modeling of Karst Conduit-Matrix Exchanges with Relevance to Contaminant Transport and Chemical Reactions
John L. Wilson and Katrina M. Henry, Department of Earth and Environmental Sicence, Hydrology Program, New Mexico Institute of Mining and Technology
In fluvial systems, the hyporheic zone is the subsurface volume where water enters from the stream, travels through the subsurface, and returns to the stream. It is a mixing zone that dynamically changes over space and time because of variations in channel geometry and roughness, streamflow regime and discharge, and other properties and forcings. The fundamental fluid dynamics of karst conduits are not different from streams. Karst conduits have the same features that cause hyporheic flow in fluvial systems. Karst-conduit hyporheic exchange, and related (bio)geochemical processing, then becomes a fundamental component of the karst water cycle. We present computational fluid dynamics models of karst hyporheic exchange. The conduit morphology driving the modeled hyporheic flow is that of a wall scallop and spatial variation in conduit area. The depth of hyporheic flow into the karst matrix surrounding the conduit increases with the flow rate in the conduit, and the size of the morphology driving the flow. Modeling of the residence time of matrix hyporheic exchange indicates the flow can be important for a variety of biogeochemical processes in the karst conduit-matrix system, as well as for contaminant sequestration and transformation.
Keywords: karst, spring, conduit, hyporheic, computational fluid dynamics