Studies of confluent flow in mature karst aquifers using analog models and numerical mixing cell models

As a prolific source of groundwater and a geologic medium vulnerable to contamination, karst aquifers have been studied to a great extent in many countries. However, comprehensive theoretical models for mature karst aquifers have not fully developed yet. Three analog models were constructed to study the confluent flow properties in karst aquifers. The experimental results revealed a non-linear relationship between water flow velocity and hydraulic gradient. Under circumstances where the Darcy’s law is no longer valid, finite-difference mixing cell models were proposed to simulate groundwater flow and solute transport in mature karst aquifers. They assume only the mass conservation and two mixing rules in each cell. A dye tracer test was interpreted using the developed model. By adjusting the number of cells, the water volume of each cell, and the time step, a reasonable fit was achieved. The interpreted model consists of six cells with water volume of 75 m 3 in each. The design of the finitedifference mixing cell model and the initial guess of flow circulation require some a priori knowledge of geologic and hydrologic conditions.