Using electrical resistivity tomography method to investigate fresh groundwater lenses on Dong Island, China

Abstract

[Objective] The subsurface freshwater lens of coral islands is an important resource necessary to maintain the production and living of islanders and ecological conservation. Accurately identifying the morphology of subsurface freshwater lenses on coral islands and revealing the mechanism of subsurface freshwater recharge are important bases for the assessment of groundwater resources on reefs, and are crucial for improving the management of groundwater resources on coral islands. [Methods] Taking Dong Island as the research object, this study combined with hydrogeological survey and high-density resistivity method to identify the distribution of freshwater lenses near sand barriers, and describe the brackish water interface. [Results] The results show that the freshwater lenses on the northwestern and southern parts of the island were relatively developed, and the thickness of the freshwater lenses below the sand dikes was 3-7 m. In the southeast of the island, there were also freshwater lenses developed in the higher terrain, but the thickness was thinner than in the sand barriers, and there was even no fresh groundwater in some local areas. [Conclusion] The development of freshwater lenses in Dong Island is associated with the distribution of topography and vegetation, and the water consumption by evapotranspiration of vegetation is the main factor that causes the thinner freshwater lenses in the low-lying land on the island.

Keywords

• coral island|fresh groundwater lenses|electrical resistivity tomography|fresh-saline groundwater interface|dong island of xisha islands