Abstract
Freshwater resources on small coral islands mainly exist in the form of freshwater lenses. The freshwater lens is highly vulnerable to salinization due to natural recharge variations and urbanization construction. However, it is unclear how a freshwater lens evolves under the influence of urbanization construction and which factors control its evolution. Based on the hydrogeological data of a small coral island in China, a corresponding 3D numerical model was established by the Visual MODFLOW software to investigate the formation and evolution of freshwater lenses under natural conditions. Thereby, the island reclamation scenario and impermeable surface scenario were set up and the changes in morphology and volume of the freshwater lens were analyzed. The results show the following: (1) After island reclamation and island building, the freshwater lens would reach a stable state after 25 years and the freshwater lens would also appear in the newly added part of the island with a thickness of 9.5 m, while the volume of the total freshwater lens would increase to 1.22 times that of the original island. (2) When the impermeable surface is built at different positions of the island, the reduction in the volume of the freshwater lens, in the order from large to small, is Scenario B (northeast side), Scenario A (southwest side) and Scenario C (central); with the increase in the impermeable surface area, the volume of the freshwater lens would gradually decrease and the volume of the freshwater lens would decrease by more than 50% with the impermeable surface exceeding 30% of the island area. The study has important implications for the conservation and rational development of subsurface freshwater resources on islands.
Highlights
Freshwater lenses, called as the “Ghyben–Herzberg” lenses, were first discovered by Ghyben [1] and Herzbrg [2] in a separate study of freshwater problems in coastal Europe.The freshwater lens is a freshwater body shaped as a convex lens that is formed on top of saltwater due to the difference in density between subsurface freshwater and underlying seawater [3]
The chloride (Cl ) concentration contour of 600 mg/L was chosen as the division between chloride (Cl−) concentration contour of 600 mg/L was chosen as the division between availavailable freshwater resources and saltwater
While previous studies have mostly focused on the formation of freshwater lenses under natural conditions, the effects of climate and groundwater extraction, etc., the application of our model provides a new direction for the study of freshwater lenses, which can be meaningful for managing small coral islands and understanding island groundwater systems
Summary
Freshwater lenses, called as the “Ghyben–Herzberg” lenses, were first discovered by Ghyben [1] and Herzbrg [2] in a separate study of freshwater problems in coastal Europe.The freshwater lens is a freshwater body shaped as a convex lens that is formed on top of saltwater due to the difference in density between subsurface freshwater and underlying seawater [3]. The rational development of freshwater lenses is an important foundation for the utilization of island water resources and sustainable development [4,5,6]. The freshwater lens is highly sensitive to the effects of climate change, natural disasters and human factors [7,8,9]. Experts and scholars have conducted further studies on the formation mechanism of freshwater lenses, e.g., Hubbat (1953), Clumbus (1956), Henry (1959), Glover (1964). Kaskef (1967) [10], who, respectively, used the conformal mapping method, the hydrodynamic method, the velocity vector-end curve method and the Dupuit hypothesis approximation method to simulate the saline and freshwater sharp interfaces under a steady state based on laboratory and field experimental studies. In 1992, Vacher [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
