South Floridas 730-sq-mile Lake Okeechobee has been likened to "a sleepy, fat baby, stirring into tantrums when winds rock her awake." But the dike-encircled lake also is a killer, having burst its banks in hurricanes twice in the 1920s, killing thousands. Click here to view maps
"The dike is...a testament to mans fear of water and weather. Its a symbol of the Hurricane of 1928 that killed more than 2,000 people. Storytellers that knew of the many undocumented migrants say it was more like 4,000...coffins ran short...piles of people were buried in a large pit in Pahokee...bodies were burned in the fields...piled...two heads high," from The Knowing In The Neck; Memoir of a Girlhood In The Glades, a dissertation by Deborah L. Hall, Florida State University, 2004.
|Soft. Old construction used sand, shells. Map courtesy of Southwest Florida Water.|
The disaster sparked the federal government to take over berming that had started in 1915. By the 1970s the Herbert Hoover Dike ringed the lake. The earthen wall was 143 miles long and 32 ft, 3 in. to 45 ft, 6 in. high.
The U.S. Army Corps of Engineers is confident that the dike, which protects 40,000 people, can withstand the winds of strong hurricanes. It is isolated from the sea so storm surge is limited to what the wind could do with lake water. But the engineers say heavy rains and regional flooding test the dike sorely. Leaks that began in 1995 have them worried enough to start modifying the oldest sections this fall.
"Numerous areas of the dike have seepage and piping problems when the lake elevation reaches 18.5 ft," reported an expert panel that studied the dike in 1998. The study concluded that a failure would be likely at one or more locations if the elevation reached 21 ft, a height predicted during a 100-year-flood event. It also said there would be 24 to 48 hours warning "in general," but that the dike also could fail suddenly without notice.
The wall includes porous limestone, shell and sand on a non-permeable layer of muck. The mix would not pass today, but it was acceptable at the time of construction. Still, the dike has performed for decades with little attention. But in recent years, especially in older sections, signs of instability and internal erosion that can trigger collapse have emerged. Severe leaks in 2002 and 2003 added urgency to renovation plans.
"Piping and other problems have been observed at elevation 18.5 and lower," says Brent Trauger, dam safety program manager with the Corps District office in Jacksonville, Fla. "If we exceed elevation 21, there is a potential for several failures. These improvements will protect us to elevation 26," he says. Corps studies show that a failure could cause a 1,000-ft breach and spread 5 ft of water over 40 square miles of towns and farmland.
After design tests, the Corps on Sept. 30 awarded a 4.6-mile contract for the first of four contracts over the next 12 years to harden "Reach I," between Port Mayaca and Belle Glade. Later projects, not yet authorized by Congress, will continue from Belle Glade to More Haven.
The $11.7-million contract, awarded to J. E. McAmis Inc., Chico, Calif., calls for inserting a 35-ft-deep "hanging" cutoff wall in the levee and cutting a landside drainage ditch. A geotechnical fabric liner in the drain will let the inevitable seepage out, but keep precious material from washing away, says Trauger. The hanging wall and drainage ditch design was chosen partly because going deep enough to sink the wall into a non-permeable layer is too expensive.
The design also keeps the project within the current berm footprint. A 1998 estimate put the cost of a non-permeable wall with a seepage berm added to the landside at $16 million a mile, versus about $3 million a mile for the hanging-wall solution.
Engineers are concerned about static level elevations. On Oct. 17, the lake was at 15.6 ft. It hit 18.7 ft in 1947 and brushed 18.6 ft in 1995 and again in 1998. The Corps says wind-driven water temporarily has pushed the level to 25 ft, but that is not likely to trigger a failure.
With a berm height of 32 ft and more, waves are not likely to overtop the dike, either. It is long-term pressure of high water that worries engineers. That is why they keep 50,000 tons of sand, rock and stone stockpiled in 16 locations.