CANAL POINT -- 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.
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.