for National Geographic News
An alarming engineering report on the 140-mile (225-kilometer) dike around Florida's Lake Okeechobee has prompted emergency management officials to prepare evacuation plans for 40,000 residents living near the lake.
Consulting engineers Leslie Bromwell, Robert Dean, and Stephen Vick wrote in their April report that the Herbert Hoover Dike "poses a grave and imminent danger to the people and the environment of south Florida."
The engineers say the dike, which is about 250 feet (76 meters) wide at its base, could fail during a hurricane or even if the lake level becomes too high.
At 730 square miles (1,900 square kilometers), Okeechobee is the second-largest freshwater lake in the continental United States, behind only to Lake Michigan.
Flooding from the lake, which is almost as big as Rhode Island, could kill hundreds. Lake water would cover tens of thousands of acres and possibly contaminate water supplies for nearby West Palm Beach, Fort Lauderdale, and Miami.
The Everglades, which adjoins Lake Okeechobee, could be irreversibly damaged as well (map of Florida).
"Recovery could take years, with indirect losses far exceeding direct damages and likely running into tens of billions of dollars," the report says.
Construction of the dike started in 1930 after powerful hurricanes in 1926 and 1928 sent floodwaters churning out of the lake. Combined, the storms killed about 4,000 people around the lake.
The dikenow holding in a major water reservoirwas intended to be only a protective barrier and was built of porous earth dredged from the lake. The dike sits on subterranean limestone, which also is porous.
"The basic problem is simple," the authors say. "Certain geologic formations that underlie the dike, and portions of the material that comprise it, bear a striking resemblance to Swiss cheese."
The U.S. Army Corps of Engineers is responsible for maintaining and repairing the dike. The corps has known about the dike's shortcomings for some time, but the problems were less well known outside the federal agency.
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