Abstract: The rough walls of karst conduits may lead to tailing phenomena in breakthrough curves. Investigating the impact of rough conduit walls on solute transport is essential for accurately interpreting field breakthrough curves and predicting solute migration processes within karst conduits. This study conceptualizes field karst conduits as an indoor conduit system, using acrylic tubes with sandy inner walls to represent rough karst conduits. Various lengths of rough tubes were designed to study the effect of tube length on breakthrough curves through tracer experiments. The experimental breakthrough curves were simulated using a two-region non-equilibrium model and a temporary storage model, analyzing how model parameters varied with rough tube length. The results indicate that: 1) As the length of the rough tube increases, the peak arrival time of the breakthrough curve advances. Compared to non-rough conduits, the width and tailing extent of the breakthrough curve for rough conduits significantly increase. 2) Both models can effectively simulate the breakthrough curves (NSE>0.99); as the rough tube length increases, the dispersion and flow rate in the flow zone or main channel gradually increase, while the cross-sectional areas of both the main channel and storage zone gradually decrease. The exchange coefficients between the flow zone (main channel) and stagnant zone (storage zone) gradually increase. 3) As the length of the rough tube increases, the proportion of the flow zone (main channel) gradually decreases, which is the primary reason for the greater tailing in the breakthrough curve of rough conduits compared to non-rough conduits.

Key words: karst conduit, rough conduit length, tracer experiment, solute transport, model parameters