Saltwater Intrusion

Saltwater intrusion is the movement of seawater into freshwater bodies, including coastal aquifers, estuaries, and river channels. In aquifers a denser saltwater wedge underlies the lighter freshwater, with the interface position described by the Ghyben-Herzberg relation, where depth of fresh water below sea level is about 40 times the height of the freshwater table above it. Over-pumping of groundwater and reduced river discharge let the wedge advance inland, salinizing wells and soils. In estuaries the salt wedge migrates upstream during low river flow and rising tides. Sea-level rise and drought both increase intrusion, threatening coastal water supply and agriculture.