Analytical, numerical, and experimental studies on the performance of low-permeability shoreline barriers on enhancing groundwater extraction in strip island aquifers

The strategy of using low-permeability barriers along the shoreline of oceanic islands was proposed recently and demonstrated effective in enhancing fresh groundwater storage. However, the effect of low-permeability barriers on groundwater extraction in island aquifers remains unknown and requires further investigation. By assuming a pumping well located at the center of a strip island with low-permeability shoreline barriers, we develop analytical solutions for the critical pumping rate (at which the seawater cone just reaches the bottom of the well) and the location of the steady-state freshwater-seawater interface under the critical pumping rate. The proposed analytical solutions are verified with numerical and experimental results, showing good agreement. The results also confirm the existence of critical barrier depth, beyond which a partially penetrating barrier can yield the same critical pumping rate as a fully penetrating barrier. The critical barrier depth is determined analytically, smaller than that required for achieving the maximum fresh groundwater volume (i.e., without pumping). Sensitivity analyses show that the critical pumping rate initially increases and then decreases as the barrier width increases, where the critical barrier width corresponding to the maximum critical pumping rate can be determined analytically. Our study presents an analytical tool for preliminary assessments of groundwater extraction in barrier-embedded island aquifers, thereby providing essential guidance for the design of shoreline barriers for improving groundwater availability and sustainability.