MODELING THE EFFECTS OF SEA LEVEL CHANGE ON SUBMARINE GROUNDWATER FLOW IN THE CHESAPEAKE BAY REGION

Submarine groundwater flow can be an important component of the hydrological and hydrochemical budgets in coastal settings. The Chesapeake Bay is a large estuary along the U.S. Mid-Atlantic Coast with a watershed that extends from New York through southern Virginia, including the Delmarva Peninsula. The average depth of the Bay is a shallow ~5-10 m. Several major rivers, including the Susquehanna, Potomac, York, James, and Rappahannock, drain into the Chesapeake Bay. Geologically, permeable coastal plain alluvium is predominant in much of the area directly surrounding the Bay. In general, the topography of the encompassing land has a small gradient, particularly in the lower reaches of the estuary. This study investigates how submarine groundwater discharge flow patterns in the area of the Chesapeake Bay could be affected by changes in sea level. A series of two-dimensional numerical models calculate submarine groundwater flow patterns for varying locations along the Chesapeake Bay, ranging from the north to the south. The numerical models are roughly shore-perpendicular, with one boundary in the subaerial region and another in the submarine zone. For each model, the land surface elevation and estuary bathymetry are based on measured topography, and hydrogeological structure and parameters are extracted from published literature. Models are calculated for both the western and eastern margins of the Bay. After calculation of these “baseline” models, a second set of models is calculated in which sea level is increased by each of a series of assumed values. The effect of increased sea level on submarine groundwater flow patterns is quantified, including changes in flow velocity, the horizontal extent of submarine flow patterns, and the locations of recharge and discharge zones.