SIMULATIONS OF THE EFFECTS OF SEA-LEVEL RISE ON GROUNDWATER LEVELS, NEW HAVEN, CONNECTICUT

Global sea level rose about 170 millimeters (mm) during the 20^th century. Since the 1960s, sea level has risen, about 115 mm, at a rate of 2.56 mm per year at Bridgeport, Connecticut. With continuing global climate change, the rate of sea-level rise is expected to increase along the northeast coast of the United States through the 21^st century.

An increase in sea level will cause groundwater levels in coastal areas to rise in order to adjust to the new conditions, potentially affecting subsurface infrastructure in low-lying cities. Additionally, some global climate models predict a wetter climate in the northeastern United States which could exacerbate the rising groundwater levels.

This study addressed the effects of sea-level rise on groundwater levels in New Haven, Connecticut. The aquifer materials consist of generally coarse over fine glacial meltwater sediments. Groundwater flows from a divide in central New Haven toward the tidally influenced Mill and West Rivers in the east and west, New Haven Harbor in the south, and the Beaver Ponds in the north.

A preliminary steady-state model of groundwater flow of part of New Haven Connecticut was constructed using MODFLOW-2000 to simulate current and future groundwater levels based on a scenario with a rise of 0.91 meter (m) (3 ft) in sea level, which is predicted for the end of the 21st century. A second simulation was run assuming a 0.91-m rise in sea level combined with a 12-percent increase in groundwater recharge.

The current models are preliminary tools to assist in framing further questions. Additional modeling with added complexity may be able to simulate the position of the current and future freshwater/saltwater interface, as well as investigate the relations among sea-level rise, aquifer stratigraphy, the effects of subsurface infrastructure on groundwater flow paths, and the water-level response of the aquifer with time.

Under the first scenario, simulated groundwater levels near the coast rose up to .91 m; this increased water level diminished toward a discharge area at the only nontidal stream near the northern boundary of study area (Beaver Ponds Park). In the second scenario for increased sea level and recharge, the effect of the simulated future rise in sea level shifts inland and simulated groundwater levels were as much as an additional 0.3-m higher at some locations.