Abstract
On islands, such as the Okinawa South-West Islands, freshwater lenses that can be found in the upper layers of underground aquifers are important water sources. However, their availability is expected to decrease significantly due to the sea-level increase caused by global warming. As freshwater is pumped from lenses, the phenomenon of saltwater up-coning may occur and may potentially lead to the entry of saltwater into the freshwater wells and the contamination of the abstracted water. In this study, hydraulic coefficients in the catchment bowling were estimated by numerical experiments and the amount of water up-coning was evaluated by numerical simulations solving the three-dimensional density-dependent groundwater flow coupled with salinity transport. Several well configurations were investigated and relevant experimental data from an actual water-pumping site were used. Results show that it is possible to design well structures to efficiently avoid saltwater intrusion, taking into account the pumping rate and the distance between horizontal strainers among other parameters.
