Mechanism of solute transient storage between karst conduit and fissures

In karst groundwater, a common phenomenon in the solute transport process is solute transient storage. The mechanism of transient solute storage between karst conduit and fissures are revealed using a constructed physical model of conduit-fissures. Quantitative tracer tests were conducted under concentrated recharge conditions, and the solute transport processes were simulated using the Dual Region Advection Dispersion model. With enhanced concentrated recharge hydrodynamic conditions, the quantity of transient water storage in fissures tends to increase linearly; and the breakthrough curves transform from single peak to double-peaks. A negative correlation between the average flow velocity in conduit and fissures was confirmed. Breakthrough curve shapes are defined by the difference between solute retention times in conduit and fissures. The overall findings are that solute transient storage induces a tailing effect and the phenomenon of double-peaks in breakthrough curves, significantly controlling solute transport processes in karst groundwater.