Environment

Despite repairs, Lake Okeechobee dike remains a danger

 

cmorgan@MiamiHerald.com

For two decades, reports from government engineers and outside experts have reached largely the same conclusion about the Herbert Hoover Dike: The levee ringing Lake Okeechobee is a disaster waiting only for high water to happen.

Even after the U.S. Army Corps of Engineers completed a $220 million-plus overhaul to shore up its most vulnerable stretch this year, the dike remains on a national shortlist of unsafe Class 1 dams. It’s a category defined as either “almost certain to fail under normal operations” or at extreme risk of failure with high fatalities and economic losses.

The Corps’ “tolerable failure rate” for dams is once every 10,000 years. One 2011 risk assessment estimated the dike’s probable failure rate at every 14 years.

“Right now, Herbert Hoover is one of a handful of our highest priority projects and in fact the project that the Corps is investing most intensely in,’’ said Eric Halpin, the Corps’ special assistant for dam and levee safety in Washington, D.C.

Last week, with dry weather and maxed-out dumping down two coastal rivers, the Corps slowly began reversing the rain-swollen lake’s monthlong climb, at least temporarily easing concerns about the aging, leaky levee. But with South Florida entering the peak of hurricane season, a lot of fingers will be crossed over the next few months. The lake can rise far faster than the Corps can lower it. Last year, for example, Tropical Storm Isaac’s runoff drove the lake up three feet in a few weeks.

“There is still a long way to go in the wet season,’’ cautioned Lt. Col. Thomas Greco, the Corps’ deputy district commander.

‘seep’ sites

Water levels, hovering just below 16 feet, remain near all-time highs for mid-August and an inspection last week found slightly more water leaking from two past “seep” sites. The minor leaks are nothing to worry about yet, Greco said — the combined volume of three gallons a minute not even a drop in Lake O’s bucket.

But they indicate what could come with more rain. At 16.5 feet, inspections shift from weekly to daily. From there, every added inch on the lake increases pressure on the dike along with risks of more serious leaks or even a major breach.

The Herbert Hoover Dike, much of it built in the 1930s after two hurricanes overwhelmed a crude levee and drowned some 3,300 people in lakeside towns, is a massive structure. It’s 143 miles long and as broad as a football field at its base. At 25 to 30 feet high, it stands taller than most buildings in its shadow.

But an ongoing $44 million Corps project to overhaul two culverts along the southeastern shoreline illustrates the biggest underlying problem: The dike that protects surrounding communities from a lake roughly twice the size of Biscayne Bay is a mammoth but deteriorating antique that doesn’t come close to modern engineering standards.

“The Herbert Hoover Dike is a huge reservoir that benefits South Florida but it’s also a gun pointed at South Florida,’’ said Steven Vick, a Colorado-based dam safety consultant and co-author of a 2006 report commissioned by that state that branded the dike “a grave and imminent danger’’ with a one-in-six chance of failing in any given year.

The headwall of a new culvert, which allows water to flow from the lake to surrounding farms, looks like a hulking fortress, a mass of concrete and steel several stories tall and 500 feet wide. Comparing it to old culverts is like putting a vintage Army jeep next to a modern M-1 Abrams tank.

The Corps is designing the new culverts to the higher standards of a modern dam, capable of enduring the immense pressure of a 26-foot lake level. That’s more than seven feet higher than the lake has ever been and well beyond the 21-foot level considered almost certain to burst unrepaired portions of the existing levee.

The Corps is in the process of replacing half the 32 culverts around the lake that are now viewed as the greatest risk to the dike’s stability, a project expected to take until at least 2018.

But they are far from the only weak points. The massive embankments themselves hide a weakness: decades of internal erosion.

The dike was built from material dredged up along Lake Okeechobee’s shoreline — a varying mix of sand, shell, rock, muck and peat. It was built to provide seasonal flood protection but over time, it’s been turned into a holding tank for flood waters and reservoir for sugar farms.

The higher year-round water levels have exposed an aging levee to forces it was never designed to endure, said dam expert Vick.

Water seeping through cracks and crevices has cut damaging channels inside called “piping.” As lake levels and water pressure increase, the piping can grow into caverns that can potentially undermine the dike. A hurricane piling storm surge against the dike can dramatically worsen the strain.

The dike has sprung leaks in the past, with the most serious erupting when lake levels topped 18 feet in 1995 and 1998, opening numerous assorted leaks dubbed “seeps,” “boils,” and “heaves” depending on severity and type. There have even been sinkholes. In 2005, Hurricane Wilma also chewed out a massive chunk near the Pahokee airport.

The Corps has made repeated emergency repairs, always managing to prevent a serious breach.

But with the dike in continuing decline, Vick said, sandbags aren’t the solution.

“It’s like you had the little Dutch boy trying to cover 140 miles of dike with his fingers,” Vick said.

The 2006 report Vick co-authored, which was commissioned by the South Florida Water Management District, put a harsh spotlight on danger from the dike. But it was hardly the first warning. In crafting the report, the state’s experts drew on decades of damage reports and studies documenting increasing concerns from the Corps and engineering consultants.

More sophisticated risk analysis done since has not only largely validated the state report, he said, but also identified additional weak points, like the culverts.

The southern stretch from Moore Haven to Canal Point is considered at highest risk but the most recent assessments, said the Corps’ Halpin, “pretty much confirm that we have a series of deficiencies all the way around the project.’’

After the alarming 2006 state report, the Corps moved to beef up the structure and reduce pressure on it, establishing a plan aimed at keeping the lake under 15.5 feet. It’s a tricky balancing act water managers don’t always get right.

In January, the Corps finished the first major work to bolster the dike, building a two-foot-thick, 70-foot-deep concrete-like “cutoff wall’’ down the center of the dike along a 21-mile segment from Port Mayaca to Belle Glade.

Strategic steps

The Corps took other steps as well, removing foliage that can weaken the dike, fortifying land-side features and stockpiling rock at strategic spots.

Before repairs, the Corps calculated there was almost no chance of dike failure with the lake below 15.5 feet, a 45 percent probability at 18 feet and near-certainty at 21 feet.

Laureen Borochaner, engineering division chief of the Corps’ Jacksonville district office, said the work significantly bolsters the dike’s most trouble-prone segment though engineers have not yet put numbers to how much repairs may have reduced risks.

But in 2011, the Corps, balking at the $10 million-a-mile price tag for the cutoff wall, announced a new study to draw up more affordable repair options.

Borochaner said the new analysis, to be completed in 2015, will be the most comprehensive ever of the dike’s flaws and potential fixes. Some options might include shallower cut-off walls or erosion-fighting filters that would let water seep through but hold earthen material in place.

In the meantime, said Corps spokesman John Campbell, the Corps will continue replacing the high-risk culverts.

“It’s not like we’re not doing anything,” he said.

Still, the pace of repair has drawn criticism over the years from area congressional leaders, the Palm Beach County Commission, the sugar industry and others. Under current schedules, the goal of bringing the aging dike up to dam standards remains a decade or more away.

Vick said that by typical Corps standards, recent work on the dike had been “done at the speed of light.” Repairs on the New Orleans levees, he said, had been going on for a half-century.

While the Corps’ sluggish bureaucracy played a role in letting the dike go neglected for so long, Vick said much of the blame fell on Congress for failing to push for repairs or pay for them.

The Corps, he said, “really deserves a lot of credit for turning the battleship around and getting the attention this deserved.”

In the small farming towns along Lake O, there is still confidence in a dike that has withstood nearly 80 years of hurricanes and see-sawing water levels.

At the Sugar Cane Golf Club in Belle Glade, where fairways run up against the dike, the rising lake has been a hot topic — but mainly about how it affects fishing.

“This is the bass capital of the world right here,” said general manager Phil Valencia. “That’s mostly what people care about with water levels.’’

But more rain or a looming storm could change the blasé attitude.

Willie Holmes, a retired mechanic for the Sugar Cane Growers Cooperative who lives in Belle Glade, said he has ridden out hurricanes in the past. This time, said Holmes as he fished last week for crappie at Sand Cut, he’d be inclined to leave.

“If they don’t get that lake down,’’ he said, “we could be in a world of trouble.’’

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