The dike surrounding Lake Okeechobee is in good condition, according to information presented during a media briefing Oct. 19 on the Herbert Hoover Dike at John Stretch Memorial Park. Barring a late-season hurricane, the dike should hold.
With Lake Okeechobee at 17 feet (above sea level) last week, the U.S. Army Corps of Engineers (USACE) was conducting daily safety checks on the southern portion of the dike between Port Mayaca and Moore Haven, and weekly checks on the northern portion.
The southern portion is most at risk of breach, according to the corps, because land elevations are lower.
Dam Safety Manager Almur Whiting IV explained that the 143-mile earthen dam has natural seepage that increases when the water level is higher.
Before 1926, the lake had a dike on its south end and a smaller muck dike on the north end, but the water could still spread out east and west. After the state-built dike failed in the hurricanes of 1926 and 1928, resulting in the loss of thousands of lives, the federal government became involved and build the current dike, which completely encircles the lake. The River and Harbor Act of 1930 authorized the construction of 67.8 miles of levee along the south shore of the lake and 15.7 miles along the north shore. The USACE constructed the levees between 1932 and 1938. A major hurricane in 1947 prompted the need for additional flood and storm damage reduction work. As a result, Congress passed the Flood Control Act of 1948, authorizing the first phase of the Central and South Florida (C&SF) Project, a comprehensive plan to provide flood and storm damage reduction and other water control benefits in Central and South Florida. The new dike system was completed in the late 1960s and named the Herbert Hoover Dike.
The dike was built from available materials, said Mr. Whiting. He said the 143-mile earthen dam that encircles the big lake was made of sand, rock, limestone, clay and peat.
“If we were building a dike today, we would not use those materials,” he said.
In addition, as the Rim Canal was dug, the materials were stacked up to form the dike with very little compacting. The mix of materials and the lack of compacting means the dike is at risk for water to seep through the earthen berm. That’s why the corps regularly inspects the “land side” of the dike for signs of seepage.
• Condition one is saturated soil.
• Condition two is saturated soil with ponded water.
• Condition three is clear water flowing through the dike.
• Condition four is water flowing through the dike carrying soil with it, eroding the dike itself.
Before Hurricane Irma hit Florida, the lake was at 13.7 feet. In about 30 days, the lake rose 3.5 ft. to peak at 17.2 ft. On Thursday, the lake level was 17.1 ft.
Since Hurricane Irma, the corps has reported and monitored some seepage at conditions one, two and three. In some cases, clear flow seepage can help relieve the water pressure; such seepages are monitored to make sure the flow rate does not increase and that the flow is not carrying soil with it.
According to corps officials the lake has started falling in recent days, but remains at its highest levels since 2004. Since the hurricane, teams reported multiple seepage sites, eight on the south side between Moore Haven and Belle Glade and two on the north side between Lakeport and Port Mayaca. Inspectors have observed no movement of material at any of the sites, thus no flood-fighting activities have been required.
The corps has also positioned stockpiles of sand and rock at strategic locations around the dike in case emergency repairs are required.
The corps is currently releasing as much water as feasible to the east and west without causing flooding downstream; the flow is sometimes restricted due to high tides or local basin runoff.
With the lake already at 17 ft., the concern is that a late-season storm could push the lake even higher, increasing the risk of a dike breach.
“Irma dumped enough precipitation to take the lake up three and a half feet in a month,” said John Campbell, corps public affairs specialist. “Any tropical system can dump enough rain to cause concern.”
“Historically, we have seen problems when the lake has been above 17.5 feet or 18 feet,” he said. “The higher the lake rises, the bigger the risk.”
Mr. Whiting said the lake level rises slowly and, should there be a problem, they would address it with a flood warning.
He said the daily inspections should provide the information to be able to warn residents should there be a flooding risk. Should that happen, a flood warning would be sent out through the National Weather Service.
For the past 10 years, the corps has been working on rehabilitation of the dike, said Mr. Campbell.
Mr. Campbell said the dike project is a little more than half complete, including 21 miles of seepage barrier constructed between 2007 and 2013, and work is completed or underway on 26 water control structures. The official projected completion date is 2025; however, there is a tremendous desire among some state and federal interests in speeding up the process, he explained. With additional financing, it may be possible to complete the work sooner.
“The safety of the people living and working around Lake Okeechobee remains our highest priority,” stated Col. Jason Kirk, Jacksonville District Commander, in a press release issued Oct. 20. “We will continue to conduct inspections daily on the south side of the dike as long as the lake remains above 17 feet.”
“Over the past week, we have seen inflows slow to the point that we’re releasing more water out of the lake than is coming in,” said Col. Kirk. “However, we’re still seeing frequent rain events in the region and hurricane season has six weeks to go, so we must do our best to ensure storage is available to handle additional precipitation.”
The Corps continues work to rehabilitate the dike. Since 2001, the agency has invested more than $900 million in features to reduce the risk to communities surrounding the lake. This includes installation of a 21-mile seepage barrier (also known as a partial cutoff wall) along the southeast part of the dike and work to replace 26 water control structures at various locations around the lake.
“Our inspectors are reporting improved performance in the area where we’ve installed the seepage barrier,” said Col. Kirk. “We look forward to resuming installation of additional cutoff wall west of Belle Glade in 2018. It is proving effective in reducing seepage.”