Solute transport in dual conduit structure: Effects of aperture and flow rate

Abstract

A typical karst aquifer configuration is the multiple conduit structure. However, it remains to be investigated how the aperture distributions and the flow rate should influence the transport process in the multiple conduit structures. To better understand the transport process in the multiple conduit structures,11 lab-scale dual-conduit structures are manufactured by varying the apertures of the two conduits (h1 and h2 denote the aperture width of the shorter conduit and the longer conduit respectively). Solute transport experiments of three different flow rates are conducted on these structures. As the flow rate increases, the dual-conduit structures are more likely to present dual-peaked BTCs. The 11 structures make one exhaustive representation of the possible aperture combination of the dual-conduit structures and the transport experiments have been conducted by three flow rates (varying by 2 degrees of magnitude), so the experimental results constitute a detailed material that should improve the understanding of transport processes in such structures. Two numerical models, Weighted Sum Advection–Dispersion Equation (WSADE) and Dual Region Mobile Immobile Model (DRMIM), are applied to fit the experimental BTCs in order to obtain some insight into the actual solute-transport processes by exploring the calibrated model parameters. Considering the possible effect of solute detention, we initially applied the DRMIM model. This DRMIM better replicated the experimental BTCs than the WSADE. This study suggests the karst community shall take the DRMIM as one candidate transport model for characterizing the dual-peaked BTCs obtained in karst aquifers.