Lake Okeechobee | disaster simulation

Computer simulation shows flooding threat from Lake O dike failure

 

cmorgan@MiamiHerald.com

A breach of the Herbert Hoover Dike would almost certainly rank as a catastrophe — but the scope and scale of loss would vary widely depending on where and when it burst and how much water was in Lake Okeechobee.

If the worst did happen, the U.S. Army Corps of Engineers, regional emergency managers and local leaders hope they have taken steps to — at the very least — minimize the death toll.

“I would like to hope and pray that it’s not as much a life safety issue anymore,’’ said longtime Palm Beach County Administrator Robert Weisman.

After Hurricane Katrina overwhelmed the protective levees surrounding New Orleans and killed some 1,800 people in 2005, South Florida emergency managers for the first time drew up mass evacuation plans for towns that suffered deadly flooding from Lake Okeechobee during hurricanes in 1926 and 1928. The Corps, meanwhile, says it has strengthened the dike’s most vulnerable 21-mile stretch.

But at high water levels, the dike remains a high-risk hazard for potentially devastating flooding. A major failure could send torrents through lakeside towns and muddy water to the suburban outskirts of Palm Beach County.

‘So many variables’

Corps spokesman John Campbell said it’s difficult to predict what might happen. “There are just so many variables,’’ he said. “A lake at 17 feet is going to be very different than a lake at 20 feet. Certainly, the higher the lake level, the more that would actually be felt.’’

A hurricane battering embankments or pushing the lake over the levee could also multiply the threats.

A Corps-funded simulation of breaches presented at a 2011 national dam safety conference mapped out huge swaths of lakeside land vulnerable to flooding. The simulation underlined what history has already shown. The biggest threats and impacts would come along the southern bank, where the dike protects 40,000 residents living along the lake’s most populated stretch from Clewiston to Pahokee.

In an extreme worst-case failure, the simulation extended flood waters more than 20 miles, spreading south and east across an expanse dominated by sugar farms. The deepest pools would collect in areas that have subsided by several feet after decades of farming on eroding peat soils that were once Everglades marsh. Much of the area is still farmed but homes and apartments also have been built in some of the lowest-lying areas near the lake.

The modeling suggests elevated roads, railroad tracks and levees would help contain much of the water as it neared western Palm Beach County’s suburbs.

The presentation included maps only for a breach at 25 feet. That’s far above the historic high of 18.8 feet and the 21-foot level where engineers predict the existing levee would fail.

While federal engineers openly discuss dike deficiencies the Corps remains reluctant to provide details, maps or modeling of the potential consequences of a failure, citing security concerns heightened since the 9/11 terrorist attack.

“We try and balance the risk of making sure the public is informed, and keeping the public safe with operational security of not allowing others to know what our vulnerabilities are,” said Laureen Borochaner, engineering division chief of the Corps’ Jacksonville office, which monitors and maintains the dike.

After receiving questions from the Miami Herald about the 2011 presentation, the Corps removed it from the website of the Association of State Dam Safety Officials. The Corps last week also rejected requests to review dike inspection reports and in 2006 refused to make flood maps public after a critical 2006 state-commission study of the dike.

The Corps, Borochaner stressed, does share flood maps with emergency managers

She also cautioned that simulations can be misinterpreted. The 2011 presentation, for instance, was designed to compare computer models, she said, not map the path of an actual breach.

Still, she acknowledged the simulation gave “general information about areas that could be inundated.”

While anything or anyone directly in the path of billions of gallons of roaring water would be in danger, Vince Bonvento, director of public safety for Palm Beach County, said that with a vast area to absorb runoff, he doesn’t anticipate lakeside towns would experience the deadly flooding of Katrina.

‘wading in water’

“What happened in New Orleans, that’s not going to happen with a breach of the dike out there,’’ Bonvento said. “People obviously would be wading around in water but not to the point where their houses would be covered.”

The worst scenarios he has been informed about, he said, would bring “minimal flooding’’ as far as 20 Mile Bend, a landmark corner of State Road 80 halfway between Lake Okeechobee and West Palm Beach.

Emergency managers and the Corps also say they’re now better prepared for a disaster.

Federal engineers will issue watches and warnings about dike conditions to local leaders and emergency managers with the goal of providing lead time before a looming failure. But ultimately, said Campbell, local emergency managers must make any call to evacuate.

Bonvento said he considers the chances of a dike failure “slim.” Still, with the lake hovering near 16 feet, a Category 2 or stronger hurricane tracking from the east or west toward Lake Okeechobee would concern him. He said he’d be inclined to order lakeside communities to get out. “I think we would still err on the side of caution,” he said.

Evacuations are common in coastal South Florida but a mass evacuation around Lake Okeechobee would be unprecedented, calling for school buses to ferry residents who can’t provide their own transportation.

“From an emergency management perspective, it puts a lot more pressure on us to have to decide on evacuating the Glades cities,’’ said county administrator Weisman. He hopes any breach would come in an isolated area and with plenty of warning. “If it happened during a storm, it would be a horrible situation because getting the resources together and trying to get people out of there would be a nightmare.’’

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