Laboratory experiment and simulation of solute transport affected by different grades of fissures and water storage of waterlogging in karst depression

The karst depressions are widely distributed in southwest China. In this area, the karst groundwater is the main water resource for the local residents to live and produce. Studying the solute transport and response law in the fissure system under karst waterlogging conditions can provide a scientific basis for karst groundwater pollution prevention and control peak-cluster depression. Based on similarity principle, a laboratory physical model of karst depression-fracture system has been establishea. The solute transport processes were simulated by advection-dispersion model and impulse response model, and the effects of different grades of fissures and water storage of waterlogging in depression on solute transport were discussed. The results indicate that the large fissure is performed as the priority flow channel, which plays a major role in controlling solute transport. The small fissures play an important role in adjusting the transient storage and slowing release in solute transport process, and the superposition processes of solute transport in small fissures makes the trailing more obvious in breakthrough curve at the total outlet. As water storage of waterlogging increases, the dilution effect enhances dramatically, which leads to the gradual decrease of solute peak concentration, the time extension of solute concentration returning to the background value, and the increase of the delay-release solute mass. This physical simulation model is a new exploration of pollutant transport in complex karst depression systems, which deepens the understanding of solute transport process in karst water system under waterlogging conditions in depression with surface pollution.