Modeling Groundwater Inundation Under Sea-Level Rise Scenarios in the Surficial Aquifer of Bogue Banks, North

Abstract

Bogue Banks in North Carolina is expected to be impacted by sea-level rise, but the impact on the subsurface groundwater system is not well understood. A three-dimensional Visual MODFLOW steady-state model and ArcGIS 10.3 were used to quantify the extent of marine and groundwater inundation by the year 2100. Visual MODFLOW was used to simulate the water table on Bogue Banks, first at current sea-level then at different sea-level rise scenarios. The results from Visual MODFLOW were then imported into ArcGIS to calculate the area inundated by marine and groundwater inundation. Sea-level rise between 0.2 and 1.4 m above present conditions may occur at Bogue Banks and seven scenarios were envisioned as appropriate intervals to forecast. A total of 29 monitoring wells were installed in the surficial aquifer of Bogue Banks and equipped with water level loggers to collect groundwater data. Aquifer properties were constrained by studying sediment cores collected during well construction. Marine and groundwater inundation combine to impair 33% to 79% of the island by the year 2100, with 43% to 51% of the island being inundated in the most likely scenarios of 0.4 to 0.6 m of sea-level rise above current conditions. Marine inundation estimates range from 5% to 31% with 11% to 17% inundation in the most likely scenarios. Groundwater inundation estimates ranged from a minimum of 28% to 48% of the area not impaired by marine inundation, with the most likely range indicating 33% to 40% inundation. The results indicate that as sea-level rise increases in severity, groundwater inundation covers a much larger area of the island than marine impairment. The results of the study therefore suggest that as sea-level rises, residents of Bogue Banks may need to account for marine and groundwater inundation as the environment changes and sea-level rises. A greater understanding of the combined impacts of groundwater and marine inundation on barrier islands may be useful for coastal residents in mitigating or adapting to changes due to sea-level rise not just in North Carolina, but globally.