Experimental study of hydrodynamics of groundwater flow in karst aquifers

A large-scale laboratory model is constructed to simulate a karst aquifer. Three groups of experiments are conducted to study the matrix-conduit exchange and how head difference, conduit size, and matrix/conduit gradients affect it. The findings can be summarized as follows; (1) In experiments with higher matrix head, a counterintuitive head inversion, where conduit head becomes higher than matrix head, occurs when the matrix-conduit head difference is small (less than 9.3 cm and 11.5 cm for the 1-inch and 2-inch conduits, respectively); (2) Flow exchange is positively related to rescaled head difference (RSHD), a parameter combining the effect of matrix and conduit gradients and the matrix-conduit head difference; (3) When the conduit has the higher head, the flow exchange is on average 2.8 times higher than when the matrix has the higher head; (4) Doubling the conduit size doubled the flow exchange and increased the length of the head inversion.