A Comparison of Methods for Assessing Groundwater Flooding Due to Sea Level Rise

Abstract

This technical note compares two groundwater flooding assessments for a site on the Rockaway Peninsula of New York City, a coastal barrier island subject to several climate change risks including groundwater flooding. One assessment was performed using a MODFLOW groundwater model while the other used an interpolated water table map constructed in GIS. The two methods showed minor differences in estimates for the current position of the water table. Likewise, the position of the water table later in this century due to 0.75 m of sea level rise indicated similar groundwater levels as well as similar patterns of emergent wetlands. Both methods yielded the same insight that widespread groundwater emergence is expected in the study area within the next 50 years. This suggests that for settings with similar topology and hydrogeological conditions, such as sandy barrier islands and low-lying coastal plains, simple water table mapping techniques are a reasonable alternative groundwater flooding assessment tool comparable to full groundwater models which can be time-consuming and expensive to create.