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Saltwater Intrusion |
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Under natural conditions, the seaward movement of freshwater prevents saltwater from encroaching coastal aquifers, and the interface between freshwater and saltwater is maintained near the coast or far below land surface. This interface is actually a diffuse zone in which freshwater and saltwater mix, and is referred to as the zone of dispersion (or transition zone) (figures 2 and 3). Ground-water pumping can reduce freshwater flow toward coastal discharge areas and cause saltwater to be drawn toward the freshwater zones of the aquifer. Saltwater intrusion decreases freshwater storage in the aquifers, and, in extreme cases, can result in the abandonment of supply wells. Saltwater intrusion occurs by many mechanisms, including lateral encroachment from coastal waters and vertical upconing near discharging wells (figure 4 and figure 5). |
Figure 2 -- Ground-water flow patterns in an idealized aquifer |
Figure 3 -- Zone of dispersion in the Biscayne aquifer |
Figure 4 -- Vertical movement (upconing) at a discharging well |
Figure 5 -- Vertical movement of saline water in the Floridan aquifer system |
For more Information, Contact |
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Paul Barlow, Coordinator Atlantic Coastal Zone Assessment U.S. Geological Survey 10 Bearfoot Road Northborough, MA 01532 (508) 490-5070 |
pbarlow@usgs.gov |
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