‘Armored’ Levees Geared to Withstand Nature’s Worst

By Curtis Morgan

When it’s done, the reservoir northwest of the Broward County line will cover an area the size of Boca Raton and hold more water than all but a handful of the state’s lakes.

It’s the biggest of seven huge basins to be built over the next five years as part of the Everglades restoration effort. All that water — 62 billion gallons, give or take a bathtub, in the biggest one alone — will be held behind man-made levees.

If these were ordinary levees — the leaky one around Lake Okeechobee comes to unsettling mind — a string of massive reservoirs would seriously raise flooding risks in a region routinely raked by hurricanes and deluges. Two ponds — among the smallest but each still spanning 1,800 acres — will abut West Broward suburbs.

The South Florida Water Management District and the U.S. Army Corps of Engineers have scrapped a levees-as-usual blueprint in favor of concrete-hardened slopes, wave-busting steps, boulder zones and internal drains. They are confident the armoring will withstand the worst weather nightmare.

"These are engineered structures, not just random fill," said Dennis Duke, Everglades restoration chief for the Corps.

The hardened designs were in the works before Hurricane Katrina overwhelmed New Orleans’ faulty flood defenses and before engineering consultants for the state pronounced the aging Herbert Hoover Dike around Lake Okeechobee a "grave danger" to public safety. The Corps confirmed Friday that the dike was among 122 nationwide tagged as substandard.

The real and potential disasters have elevated awareness, said Tommy Strowd, assistant deputy executive director for the district, which is building the reservoirs.

"It’s evolved from the theoretical risk to a real-world occurrence," Strowd said. "It’s not a might-happen, could-happen kind of thing."

The reservoirs — intended to replenish the Everglades, reduce damaging high water in Lake Okeechobee and give the district more options to deal with water shortages and floods — will be built to the most stringent of federal standards, the ones set for dams.

A levee, depending on the project and location, is designed to handle storms that come along every 200 to 1,000 years, said the Corps’ Duke. A dam is designed to hold up against a once-every-10,000-years blow.

Duke said the agency is factoring in the most extreme possibilities — for instance, 50 inches of rainfall was reported in some areas of the Yucatan Peninsula during Hurricane Wilma in 2005.

"People are being on the safe side," Duke said. "We’re tending to go toward the upper ranges, particularly in areas that are subject to loss of life or catastrophic failures."

The new levees will be higher, harder, wider and more expensive — re-engineering added more than $300 million for all of the reservoirs, Strowd said.

At the Everglades Coalition conference last month, district Executive Director Carol Wehle called rising construction costs a growing concern for the $11 billion restoration.

With the reservoirs, engineers say, the additional strength is a necessity.

In canals and lakes, much of the water and pressure is below ground. Strowd likened the reservoirs to above-ground swimming pools, where every drop could be lost with a serious breach. When a Florida Power & Light reservoir in Indiantown burst in 1979, the flooding covered 60 square miles and did $20 million in damage.

From the outside, the grass-covered slopes around reservoirs will probably look like most of the levees along canals in South Florida. But inside, they will be substantially different.

The biggest one, the Everglades Agricultural Area reservoir in southwestern Palm Beach County, will use four times the fill of older levees.

Its 25 miles of embankment will feature a concrete slope topped by steps to break up waves that have carved out chunks of the earthen Okeechobee dike, a boulder zone backed by impervious material, and a drain system to combat internal erosion that has weakened the Hoover dike.

The Everglades Agricultural Area dike will stand 29 feet high to handle 12 ½ feet of water. The smaller West Broward ponds, just four feet deep, could wind up at 10 feet — more "freeboard" to keep wind-driven water inside.

"You get a big storm surge and waves on top of that, it sloshes right up the side," Strowd said.

The approach is a major change from practices of decades past, when the "engineering" of levees involved bulldozing whatever was dredged up in the waterways they were designed to protect. The Hoover dike, built after hurricanes in 1926 and 1928, consisted of uncompacted sand, peat and fill, much of it pumped from the lake.

Water managers consider the reservoirs key components of a $1.5 billion state program that will speed up some Everglades projects by as much as 10 years.

Environmentalists support the added safety factor, but some argue the projects seem aimed at addressing urban flooding and water-supply concerns without promising relief for the Everglades and Lake Okeechobee. In December, the Natural Resource Defense Council filed notice to sue federal agencies, contending the state deviated from restoration plans Congress approved.

John Adornato, Everglades policy coordinator for the National Parks Conservation Association, said the state has yet to offer assurance Everglades National Park will get the first dip into any stored water — "a huge problem."

Former Gov. Jeb Bush, echoed by some Florida lawmakers, urged that dam standards be applied to Okeechobee, the largest lake in the Southeast.

The Corps has repeatedly defended the integrity of the 70-year-old dike and in October revamped a $300 million plan to shore it up over the next several decades.

As it stands now, Duke said, the dike meets a nearly one-in-1,000-years storm standard.

The Corps is exploring options to reduce risk, including permanently lowering lake levels and pouring concrete "cutoff" walls inside the dike.

But upgrading the 143-mile structure to modern dam standards would need congressional approval. And the Corps, Duke said, hasn’t taken a crack at a cost estimate.

"One thing we’re trying to avoid is having to reconstruct the dike into a dam," he said. "We’d basically have to tear out the levee and build it from the ground up."