Flow dynamics and age stratification of freshwater lenses: Experiments and modeling

The development and flow dynamics of freshwater lenses are investigated by physical experiments on a laboratory scale. Using an acrylic glass box and a combination of different tracers we were able to simulate a cross section of an infinite strip island and visualize its groundwater flow patterns. For validating our model, results of the generation and degeneration of the freshwater lens were compared to analytical and numerical models. Using recharge water of different colors we were able to visualize flow paths as well as the age stratification within a freshwater lens. Flow paths in the lens could be demonstrated to remain in contact to the outflow zone at all times during the experiments. Analytical solutions are in good accordance to our findings. Additional experiments show the differences between pumping from a horizontal and a vertical well on the interface. These experiments with identical boundary conditions confirm former presumptions: A horizontal well shows less up-coning of the interface and therefore allows a higher sustainable yield than a vertical well.