Figure 3. Ground-water flow paths in an idealized coastal watershed along the Atlantic coast. Fresh ground water is bounded by saline ground water beneath the bay and ocean. Fresh ground water discharges to coastal streams, ponds, salt marshes, and tidal creeks and directly to the bay and ocean. Figure 2-1. Schematic cross-section of idealized coastal aquifers. Note that aquifers can connect with the ocean in multiple ways. From Barlow (2003).

Figure 5. Generalized ground-water flow patterns in a multilayer, regional aquifer system. The water table forms the upper boundary to the uppermost aquifer in the sequence, which is called an unconfined (or water-table) aquifer. Although the two lower aquifers also are bounded by water tables near the land surface, the aquifers are considered to be confined because each of them is overlain and underlain by confining units. Recharge occurs to the upper, unconfined parts of the aquifer system. Ground water discharges to streams, rivers, and creeks, through the floors of the ocean and bays, and to marshes fringing coastal waters. Figure 2-2. Cross-section of coastal aquifers showing fresh and salt water boundary in surficial and confined aquifers. From Barlow (2003).

Figure 21. Schematic illustration of some of the modes of saltwater intrusion in a multilayer, regional aquifer system caused by ground-water pumping at wells. Saltwater moves into the unconfined aquifer from the Atlantic Ocean and into the shallow part of the top confined aquifer from the major bay. The two freshwater-saltwater interfaces at the seaward boundary of each of the confined aquifers also move landward as saltwater is drawn inland from offshore areas. Figure 2-3. Cross-section of coastal aquifers showing migration of fresh-salt water boundary in surficial and confined aquifers as a result of pumping wells. From Barlow (2003).

Figure 7. The transition zone in the Biscayne aquifer near Miami, Florida. The transition zone was determined by measurement of the chloride concentration of water samples extracted from the bottom of monitoring wells (shown as black dots). Chloride concentrations in the transition zone increased in the seaward direction from freshwater containing 16 parts per million to seawater containing 19,000 parts per million (Kohout, 1964). Figure 2-4. Cross-section of the Biscayne coastal aquifer in Florida showing the intrusion of brackish water into areas where it can be sampled in observation wells. From Barlow (2003).