Abstract
The Komesu subsurface dam was constructed along the Pacific shoreline south of Itoman City, Oki-nawa, Japan, to provide a reservoir for groundwater in the Ryukyu Limestone aquifer and to prevent saltwater intru-sion from the sea. At present, residual saltwater remains in the reservoir and has not yet spread out during the past 10 years since the completion of the cut-off wall. Con-tinuous monitoring of the groundwater level and electrical conductivity measurements showed that the electrical con-ductivity of the stored groundwater along the cut-off wall increased drastically during the rainfall events. This find-ing suggests that upward movement of the residual salt-water was associated with the groundwater flow over the cut-off wall, as previous studies have noted.
