Experimental and modeling investigation of pumping from a fresh groundwater lens in an idealized strip island

Abstract

Groundwater lens floating on the seawater in surficial coastal aquifers is an important freshwater supply for small island inhabitants. This study addresses an unanswered, simple but important question for groundwater resources management in small islands: how much freshwater can be sustainably withdrawn from a groundwater lens in small islands. We derive an approximate analytical solution to describe the freshwater-seawater sharp interface profile in an idealized strip island subject to a pumping well located at the domain center to determine the critical or maximum allowable pumping rate that prevents saltwater upconing. A simple formula of the critical pumping rate is provided as a function of hydrogeologic parameters, including the recharge rate, densities, hydraulic conductivity and well penetrating depth. It shows that the critical pumping rate increases linearly with the recharge rate and decreases linearly with the hydraulic conductivity and the squared well penetrating depth. Laboratory visualization experiments and numerical simulations were conducted to validate the derived analytical solution. Results indicate that the maximum pumping rate can be as high as 50% of the total recharge for a single well located at the top of the domain center. Our solutions and results provide useful insights for sustainable groundwater management in small islands and can potentially render significant social and economic impact for inhabitants on small islands.