Effects of Sea‐Level Rise on Ground Water Flow in a Coastal Aquifer System

Abstract

The effects of sea-level rise on the depth to the fresh water/salt water interface were simulated by using a density-dependent, three-dimensional numerical ground water flow model for a simplified hypothetical fresh water lens that is similar to shallow, coastal aquifers found along the Atlantic coast of the United States. Simulations of sea-level rise of 2.65 mm/year from 1929 to 2050 resulted in an increase in water levels relative to a fixed datum, yet a net decrease in water levels relative to the increased sea-level position. The net decrease in water levels was much greater near a gaining stream than farther from the stream. The difference in the change in water levels is attributed to the dampening effect of the stream on water level changes in response to sea-level rise. In response to the decreased water level altitudes relative to local sea level, the depth to the fresh water/salt water interface decreased. This reduction in the thickness of the fresh water lens varied throughout the aquifer and was greatly affected by proximity to a ground water fed stream and whether the stream was tidally influenced. Away from the stream, the thickness of the fresh water lens decreased by about 2% from 1929 to 2050, whereas the fresh water lens thickness decreased by about 22% to 31% for the same period near the stream, depending on whether the stream was tidally influenced. The difference in the change in the fresh water/salt water interface position is controlled by the difference in the net decline in water levels relative to local sea level.

Impacts of Future Climate Change and Baltic Sea Level Rise on Groundwater Recharge, Groundwater Levels, and Surface Leakage in the Hanko Aquifer in Southern Finland

“…In contrast, the observation wells in the middle of aquifer area showed small or insignificant influences of sea level on groundwater level. Previous studies on the impacts of future sea level rise on groundwater quality and groundwater resources have reported that these will mainly take place along the coastline, main rivers and drainage canals in low-lying aquifers [5,6,70,71]. Those studies also reported the influence of stream types and tides on the groundwater level of aquifers along the coastline, with higher groundwater levels in response to sea level rise causing more discharge into the streams.…”

Development of a numerical model to simulate groundwater flow in the shallow aquifer system of Assateague Island, Maryland and Virginia

“…These DRN cells remove water from the groundwater system when the water table intersects land surface, thus preventing the water table from rising above the land surface. This method does not provide for the development of new surface-water bodies but does allow for a more physically realistic analysis of the response of the underlying freshwater-saltwater interface in response to a changing sea-level position because it is the altitude of the water table (or surface-water expressions of the water table) above local sea level that generally determines the depth to the underlying freshwater-saltwater interface (Masterson and Garabedian, 2007;Werner and Simmons, 2009). …”

“…It is understood that as sea-level rises, the water table in shallow coastal aquifer systems also will rise, and depending on the thickness of the vadose zone, the water table may intersect land surface (Masterson and Garabedian, 2007). To account for this condition, head-dependent flux boundaries in the Drain (DRN) package in SEAWAT (Langevin and others, 2007) were assigned to every model cell above sea level with the stage height specified at the land-surface altitude of each cell (Sanford and others, 2012).…”

“…However, in addition to increased erosion and surface inundation from rising sea level, the groundwater-flow system can be substantially affected by increased water-table altitude, subsurface flooding of low-lying areas, and the potential for saltwater intrusion (Masterson and Garabedian, 2007). Understanding how sea-level rise may affect groundwater hydrology in shallow, unconfined coastal systems such as Assateague Island may be vital for assessing the potential impacts of sea-level rise on the sustainability of Federally listed endangered species, such as piping plovers.…”

The case of the Biscayne Bay and aquifer near Miami, Florida: density-driven flow of seawater or gravitationally driven discharge of deep saline groundwater?

“…), water supply from coastal aquifers in Florida and elsewhere (Anderson et al 1988;Rao et al 2004;Spechler 1994), as well in the prediction of the effects of sea level rise in these aquifers (Masterson 2004;Masterson and Garabedian 2007;Rozell and Wong 2010).…”