The Long Beach barrier island and a rising sea

Abstract

Barrier coasts have a meagre elevation above the sea and their location in front of the mainland makes them very vulnerable for sea level rise and climate changes. Barrier coasts are very prone to floods and a first line of defense against the natural violence of hurricanes and North Easter storms (nor’easters) . The Long Beach Barrier Island is located a few steps away from New York City. It is highly urbanized and has a high exposure to water related problems. Therefore, the Long Beach barrier island forms an interesting case study. This thesis aims to gain a broad and better understanding of the effects of sea level rise and climate changes on the groundwater level of the Long Beach barrier island. In addition, the study tries to find out how these changes might affect the island. To evaluate the effect of climate change and sea level rise, groundwater models have been developed in PMWIN and iMod. Scenarios are used as input for these models and are based on climate change projections of the New York Panel on Climate Change (NPCC). The model outcomes show that future climate changes and sea level rise might have a large impact on the groundwater level of the island. As climate change induces less recharge the shape of the groundwater level might become less convex in the future. On the other hand, sea level rise will result in a global rise of groundwater levels in two of the three scenarios. The model outcomes show that the shores of the island will experience the highest groundwater level rise. These changes are greatest in winter months where groundwater levels might increase with one meter at the shores. As evapotranspiration increases in summer months, groundwater levels in summers are expected to decline. The model outcomes show that seasonal differences in groundwater levels become greater. These changes in groundwater level might have a great impact on the City of Long Beach, the biggest city on the barrier island. As the islands elevation is lower on the north side than on the south side, the groundwater changes are expected to have the largest impact on the north side of the city. In this area, groundwater levels might rise critically close to the surface. The model outcomes show that in a moderate scenario groundwater levels rise within 70 cm of the surface. This could lead to uplift of pools and subsurface infrastructure and frost heave under roads and pavements. It could also affect plants and trees in the city, limiting their growth and causing diseases related to water saturated soils. The approach taken in this study can be applied to other barrier coasts and could help in better understanding the effects of climate change and sea level rise on such islands.