Solute transport experiments and modelling in terminal conduit of karst hydrosystems, Southern France

Abstract

In the community working on karst hydrosystems, the needs for subsurface solute and contaminant transport characterization is widely acknowledge.  In former studies, several researchers addressed these needs with different approaches such as laboratory experiments, field tests, and groundwater flow and transport simulations. The main objective of such approaches is to improve knowledge of transport processes in karst hydrosystems, and propose solutions to limit the downstream hydrogeological risks (contamination of water resources). In this study, we performed a solute transport experiment in different karst aquifers, in the terminal karst conduit near the spring. We injected a dye in the karst conduit and we monitored the restitution of the tracer at three different zones downstream. In each zone, five probes were placed at different locations (middle, up, down, left and right parts of the cave) along the cross-section of the karst conduit.Experimental data allowed to reconstruct a transient spatial distribution of concentration for each zone and a general evolution of solute plume. It also provided information about dye mixing along the karst conduit. As a next step, these results are compared to simulated results to investigate the effect of karst conduit geometry, turbulent flow and velocity profiles on concentration profiles, mixing processes and the evolution of solute plume along the conduit. Preliminary results showed that the consideration of the complex karst conduit geometry and morphology has an important effect on transport processes, with a behavior notceably different from the one obtained with numerical simulations on simplified karst conduit geometries.