water encroachment is becoming acute is the Pinellas County peninsula, on the west coast of Florida. Here, sea water is gradually moving into the aquifer, destroying its worth to the farmers, municipalities, and industries that have grown to rely on it. One by one the wells are beginning to yield water unfit for use. Because of the encroachment, St. Petersburg was forced to develop a new water supply on the mainland as early as 1928, and indications are that the other municipalities of the county must follow suit before many more years. Other places at which salt water has encroached to a greater or lesser extent are Miami, Fort Myers, Fort Pierce, Tampa, Daytona Beach, Panama City, and Pensacola. The encroachment at Tampa forced the abandonment of the old municipal wells about 25 years ago, and since then Tampa has obtained its water from the Hillsborough River. However, available information indicates that an adequate supply of ground water for Tampa may yet be obtained close to the city. The encroachment at Miami was caused, not by pumping of wells, but by drainage operations (Parker, Ferguson, and Love, 1953).
An encroachment of salt water is especially lamentable because its effects are long lasting. Having once established inroads into the aquifer, the salty water will rinse out only very slowly, leaving traces for many years and perhaps for generations after remedial measures are undertaken. Convincing evidence of this is the fact that today, after thousands of years of rinsing, salty water that entered the aquifer during the ancient high seas is yet very much in evidence (fig. 19). It would seem, therefore, that among the various undesirable effects of excessive draft, an encroachment of salt water is the most hurtful. If it is not checked, it may destroy all or a part of an aquifer beyond practical recovery.
In the long run, salt-water encroachment can be avoided, whenever it impends, only by limiting the total draft from wells, but the limit can be raised by artificially recharging the aquifer. If geologic conditions are favorable, artificial recharge might be most effective if applied immediately adjacent to the coast, where it would build up a ground-water "ridge" to act as a barrier to the inland advance of sea water. This approach to the problem probably would be feasible only if the aquifer were underlain by a watertight formation at a reasonable depth. It is therefore important that the geology of the area be understood thoroughly before such remedial measures are undertaken.
As we have already observed, a withdrawal of water from the