Analytical, Experimental, and Numerical Investigation of Partially Penetrating Barriers for Expanding Island Freshwater Lenses

Abstract Freshwater lenses are of great importance in supporting both the vulnerable ecosystems of small‐to‐medium oceanic islands and the lives of local inhabitants. Recently, an engineering approach that embeds a low‐permeability, fully penetrating barrier along the shoreline was proposed and demonstrated under controlled conditions to be effective in enhancing island lens size. The current study extends that work by investigating the effect of partially penetrating barriers placed at the shoreline on both circular and strip island lenses, using: (1) sharp‐interface analytical solutions, (2) dispersive numerical modeling, and (3) sand tank experimentation. Analytical, experimental, and numerical results are in reasonable agreement in terms of the freshwater‐seawater interface. The findings indicate that partially penetrating barriers of sufficient depth (i.e., the freshwater depth in barrier from the fully penetrating barrier case) produce comparable results to fully penetrating barriers, and therefore, the former is more cost‐effectiveness. Moreover, the minimum barrier depth (i.e., the “critical depth”) required to obtain approximately the same lens as that achieved using the fully penetrating barrier is estimable from the analytical solution, as verified by laboratory experiments and numerical simulations. The sensitivity analysis based on the analytical solution indicates that a lower barrier permeability and a greater barrier thickness, which lead to a higher freshwater storage (as expected), require a larger critical depth. The guidance on the design of partially penetrating shoreline barriers arising from this research adds to existing engineering techniques for enhancing freshwater resources on circular and strip islands.