National Geographic : 1967 Oct
the next three years, increasing the lake's safe storage capacity by more than a million acre-feet. Meanwhile, over the years, they have de signed and built an elaborate system of levees and canals to keep Lake Okeechobee from ever reaching danger depth. Before the hurri cane season each year, billions of gallons are drained to the Atlantic and the Gulf of Mexi co (maps, page 518). Working closely with the Engineers is an energetic state agency, the Central and South ern Florida Flood Control District, created in 1949. Besides helping to control floods, its duties include assuring all hands an ample supply of fresh water. As resort cities burgeoned along the coast, demand for water had grown enormously. Some Miami area residents a few years be fore had had a startling experience: When they turned on their faucets, the water from their wells came out salty-undrinkable. What had happened? Miami and much of this coast lies on a series of rocks composed mostly of porous limestone. Geologists call the formation the Biscayne aquifer-literally, "water carrier." Fresh water flows through it as if through a sponge. But the sea presses in from the other side, and if the sweet water has too little force, salt water will invade the aquifer. That's what had happened when the taps flowed salty. Dam-borne Road Cuts River of Grass To keep this vital sponge full of sweet water and to store reserves for unrainy days, the Corps of Engineers and the Flood Control District have created a vast system of shal low, grassy reservoirs, called conservation areas, north of the park. Open to the public, these areas preserve thousands of acres of glades country for hunt ing, fishing, camping, boating, and other rec reational use. But inevitably they interrupt the natural flow of the river of grass south ward into the national park. This became agonizingly apparent after 1962, when completion of Conservation Area 3, just north of the famous Tamiami Trail, resulted in the building of an earthen dam along the park's northern boundary. The dam, or levee, with the road on top, replaced a nine-mile section of the old Trail (page 520 and map, page 519). The Engineers built six sets of gates in the levee-four to release water into the park and two as emergency outlets from the conservation area. During the years that followed, the gates 516 were kept closed much of the time, and the park found itself gasping for water, especially in the tragically dry spring of 1965. Last spring drought again stalked the Everglades, but this time the state requested that the gates be kept open. Result: a greatly reduced kill of fish and other wildlife. Recurring cycles of drought and flood are nothing new to the Everglades. June and July usually bring rains which reach a climax in the autumn hurricane season. In late winter and spring the Glades dry up. All creatures dependent upon fresh water congregate in ever-shrinking sloughs and water holes. Rainfall directly upon the park has always (Continued on page 522) Danger on the horizon: Fire Control Aid Ralph Johnston, left, and Ranger Erwin Winte keep a sharp watch from the Shark Valley Observation Tower (page 553). Especially in times of drought, a carelessly discarded cigarette or match, a camper's fire, or lightning can kindle the saw grass. Sighting along an Osborne fire finder, Mr. Johnston determines direction and distance of smoke, then directs fire fighters to the scene by air and land. Glades fire (right), raging north of the park, consumes all vegetation. Sometimes even the peat soil burns.