Can Lake Okeechobee’s aging dike handle what could come from Hurricane Dorian?
Heavy rain over and around Lake Okeechobee can spell trouble for South Florida’s decades-old flood control systems. With Hurricane Dorian’s projected path potentially crossing north of the massive lake, rain and runoff are likely to raise water levels and pressure on the aging dike that rings Lake O.
Still, state and federal water managers say they’re confident the dike and system can handle what Dorian may deliver.
“We are in a good position now, considering current forecasts,” said Drew Bartlett, executive director of the South Florida Water Management District. “I feel like the lake could absorb a hurricane and the rain wouldn’t threaten the dike either.”
Jeff Byard, associate administrator for the Office of Response and Recovery at the Federal Emergency Management Agency said the Corps, which manages the lake, “feel like they’re in good shape with the amount of rain that could fall.”
Byard said he had talked to Corps representatives earlier on Thursday.
When Hurricane Irma hit two years ago, levels in the 730-square-mile lake — the largest in the Southeast — shot up 3 1/2 feet to 17.2 feet. That level increases regular inspections of the aging Herbert Hoover Dike from weekly to daily. Irma’s initial rainfall wasn’t the real problem, it was all the stormwater runoff flowing down wetlands, canals and the lake’s recharge areas over the following weeks.
The district estimates Lake O could rise by one foot if Hurricane Dorian dumps between 8 inches and 10 inches of rain on the watershed. The lake is currently at 13.6 feet. The resulting rain and runoff from could potentially put up to two feet of water in the lake, but it’s still early to tell how severe rainfall will be and for how long the storm will linger in the area, Bartlett added. That would be remain below serious levels of concern for the dike.
According to a 2000 Corps study, the risks of a dike failure rise significantly at 17 feet. At 18 feet, the probability is 45 percent. At 20, a breach somewhere along the dike is likely, with damaging and potentially deadly flooding. That study was done before ongoing projects to shore the structure up. Since 2001, the Corps has spent more than $950 million on overhauling the weakest points, constructing massive new flood gates in the dike and other work. Hundreds of millions in other projects are in the pipeline as well.
Still the dike remains high-risk because of its age and construction made of sand, rock, shells and other out-dated materials.
The lake has topped 18 feet a handful of times in the past. It peaked at 18.8 feet in 1995, an event that opened serious leaks at nine spots along the south and southeast shorelines, and again topped 18 feet after a string of hurricanes in 2004. In 2005, Hurricane Wilma chewed a chunk from the dike near the Pahokee airport. The Corps cited an old repair job that failed and said the dike was not at risk of a breach.
Water managers were lowering canal levels ahead of the storm, creating capacity to take in heavy rainfall and preparing South Florida’s flood control systems for increased volume. The District will close all navigation locks on the lake on Saturday at 3 p.m. as it prepares for the storm, according to an advisory to boaters navigating to and from Lake Okeechobee and the Kissimmee River and Upper Kissimmee Chain of Lakes.
The U.S. Army Corps of Engineers still hasn’t made any decisions about releases to manage water levels on the lake ahead of Dorian, according to spokeswoman Erica Skolte. Releases in the past have been blamed for damaging algae blooms in the rivers that are the lake’s two pressure relief valves - the Caloosahatchee on the west and the St. Lucie on the east.
Hurricanes can have other impacts on Lake O as well, with rain and runoff and waves stirring up polluted sediment from the bottom and worsening water quality. Vegetation can also be uprooted, removing a protective boundary that separates the lake’s turbid interior water from cleaner water around the fringes.
South of the lake, the concern is that excess water could flood vast conservation areas where tree islands provide shelter for deer and nesting wading birds across more than 1,300 square miles.