(a) The laboratory setup scheme. The main flow chamber simulates the aquifer, and the two side chambers create the boundary conditions during the experiments. The left chamber represents the saltwater boundary at the seaside, and the right chamber represents the inland freshwater boundary of the regional aquifer. (b) A picture of the laboratory aquifer. 168 electrodes are placed for in situ voltage measurements, which are equivalent to the salinity of the water. The electrodes, whose numbers are written, are discussed in the text. Four sensors of water content (WC1-WC4) are placed in the capillary zone above the water level. Four piezometers (P1-P4) are located a few centimeters below the water table at different distances from the left boundary. Two divers (WL1-WL2) are placed in the water chambers.