The impact of sea-level rise on saltwater intrusion for barrier-island aquifers in North Carolina

Abstract

Saltwater intrusion is an increasing problem for coastal aquifers due to rising sea levels, especially in areas of low hydraulic gradient, such as barrier-island aquifer systems. Large-scale studies are particularly useful for identifying trends in the effects of sea-level rise, especially for relatively understudied barrier-island aquifers. The barrier islands of coastal North Carolina, U.S.A., lie in a hot spot of sea level rise, where rates are projected to exceed global means throughout this century. Herein, we present a study of the effects of sea-level rise using four primary study sites, each with varying hydraulic properties, island width, and rates of sea-level rise. We use these sites to understand the viability of barrier-island aquifers in North Carolina, but also to understand in general the factors that are most important to the future viability of all barrier-island aquifers. We utilize a one-dimensional steady-state analytical model that allows the calculation of the position of the toe of the saltwater wedge at the base of the aquifer while limiting a rise in the water table. We determine the position of the toe for various sea-level projections up to the year 2100 and utilize this parameter as an assessment of the viability of the aquifer. Our findings suggest that higher island width and lower hydraulic conductivity are the most sensitive parameters and help to limit the effects of sea-level rise on aquifer viability. Aquifer risk maps calculated for the entire North Carolina coast, which equate risk with the position of the toe relative to island width, demonstrate that sea-level rise is projected to have increasing impact on aquifer viability over time, but that areas with narrower width and higher sea-level rise rates are the most vulnerable.