Impact of Island Urbanization on Freshwater Lenses: A Case Study on a Small Coral Island

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.

Simulation of the Movement of Groundwater in an Aquifer

“…With no statistically significant difference between the analytical and numerical solutions, the results demonstrated that the lowest intensity situation resulted in the greatest pulling rate. The findings were consistent with previous research [26,27]. Finally, the study assessed the efficiency of the numerical chart and found that the execution of the program with a low n-value produced results that were just as accurate as those with a high n-value.…”

Time Scale of the Formation of Fresh Groundwater Lens on an Atoll Island under the Influence of Land Reclamation

“… a Adapted from previous studies. ,,− Boldfaced numbers with an underline are the reference values of L 2 , b 2 , and K 3 . …”

Groundwater Response to Tide Fluctuation and Rainfall in Coastal Reclamation Area

“…However, the numerical model is limited by field data, and the combination of various methods ignores the influence of tidal fluctuation which affects the vertical flow and the release or compression of water [24,25]. Ling et al (2021) used a three-dimensional numerical model of variable density flow and solute transport to study the impact of island urbanization on FGL on a small coral island in Sansha City, Hainan Province, China. However, it overlooks environmental factors such as tides and natural disasters [26].…”

“…Ling et al (2021) used a three-dimensional numerical model of variable density flow and solute transport to study the impact of island urbanization on FGL on a small coral island in Sansha City, Hainan Province, China. However, it overlooks environmental factors such as tides and natural disasters [26]. Zhang et al (2021) developed new analytical solutions for the steady-state heads and nondispersive SFI, which considered extended situations where reclaimed soils were more permeable than the original aquifer.…”