Abstract: In order to investigate the effect of pools on solute transport in the conduit, a pool-pipe system was built in the laboratory and the breakthrough curves (BTCs) were generated through quantitative tracer tests under different conditions. The Qtracer2 program was used to obtain solute transport parameters. We use retardation coefficient R to characterize the difference between the 1-D analytical solution of classical advection-dispersion equation and the experimental results. The experimental results reveal that the peak concentration decreases with more pools in series whereas the dispersion and the dispersivity increase gradually. Adding transient storage increases retardation as tailing of the BTC grows with more pools. This demonstrates that transient storage within pools is transformed to retardation. The symmetrical pool has longer tails compared to the asymmetrical pool. The peak concentration lags behind significantly due to the asymmetrical pools. As the flow rate increases, the amount of tailing and the dispersivity decrease in any case. The 1-D analytical solution of classical advection-dispersion equation can fit BTC of the single pipe in maximum discharge well but cannot fit other BTCs with appreciable tails. Therefore, it requires an appropriate model to explain the tailing of BTC.

Key words: karst conduit, pool-pipe system, solute transport, pipe structures, flow conditions