Heavy work is needed on a structure created in the 1930's.
In what appears to be a never-ending task, U.S. Army Corps of Engineers crews in Florida continue working on the outdated Herbert Hoover Dike surrounding Lake Okeechobee — the state’s largest freshwater lake. Since 2007, teams have performed various tasks to reduce the risk of dike failure due to flooding from high water levels.
“Because of the construction methods used in the 1930s, the dike is susceptible to erosion of the earthen embankment,” said John Campbell, public affairs specialist of the Jacksonville District, U.S. Army Corps of Engineers (USACE). “Over the past six years, we have installed a 21.4 mile concrete barrier known as a cutoff wall into the southeast quadrant of the dike. The cutoff wall is designed to reduce seepage and prevent erosion.”
The cutoff wall extends from roughly 6 ft. (1.8 m) from the top of the dike through the foundation to several feet beyond the limestone bedrock, averaging between 60 to 80 ft. (18.3 to 24.4 m) below the crest of the dike. It’s considered crucial to the rehabilitation effort, although is by no means a solution to a complex problem. Despite a multi-million dollar effort by USACE, the dike remains on a national shortlist of unsafe class 1 dams, with a category defined as either “almost certain to fail under normal operations” or at “extreme risk of failure with high fatalities and economic losses.” Campbell said progress has been made, but there is a long way to go.
“The $200 million invested so far made it possible to install the cutoff wall in the southeast quadrant of the dike between Port Mayaca and Belle Glade,” said Campbell. “While that feature reduces the risk of failure in that area, the remainder of the dike is still largely at risk. The Corps is rating the dike as a single system, and the dike is only as strong as its weakest area. Thus, it continues to be assigned an action classification of one under the Dam Safety Action Classification [DSAC] system.”
Crews are currently working on a project to remove or replace 32 culverts that serve as water control structures.
“These culverts have also experienced significant erosion of the material around them, and currently are seen as the greatest risk to the stability of the dike,” said Campbell. “Action has been taken, with either work started or contracts awarded, on 16 of the 32 culverts that were installed through the dike. We anticipate working on culverts will take us through 2018. We are also conducting the most comprehensive study of the dike to determine the remaining fixes necessary in other areas that haven’t been addressed.
“The dike is 143 miles long, and we’ve addressed the first 21 miles. It’s possible the remaining sections may need additional cutoff wall, a seepage management system or other alternatives. The study is expected to be complete in 2015, and will drive the remaining work on the dike that takes us past 2020.”
“Bauer received the notice to proceed for the first task order in May of 2008 and continues to work on the project today, said Art Hansen, an engineer of Bauer Foundation Corp. “Work has been performed on four task orders and a number of small culverts. Our work basically entailed putting in a seepage cutoff wall, up to 80 feet deep, in order to keep the water from Lake Okeechobee from leaking through the dike and undermining its integrity. On the four task orders, we were the general contractor and on the culverts, we are working as a subcontractor.
“As the general contractor, we were responsible for all aspects of the job from providing office space to the USACE to restoring the dike to its previous condition after the wall was installed. For the culverts, we were awarded the contracts because of our specialized technique and its suitability for the numerous closures that make up the culvert projects.
Work involved establishing a lay down yard with offices, cement batch plants, maintenance facilities and inventory storage facilities, according to Hansen. Bauer Foundation Corp. was responsible for widening the work platform and installing the cutoff wall using a cutter, soil mixer (CSM) after removing peat using Kelly drilling rigs. Crews had to remove the platform extension and seed the banks of the dike to return it to the pre-work condition.
The wall had to be able to stop the seepage, but also meet the elastic modulus requirement to allow it to flex as the lake level changed.
“The cutoff wall was constructed using either a Bauer RG25 or BG28 drill rigs with a BCM5, CSM attachment,” said Hansen. “The pre-drills were performed using either a Bauer BG28 or BG40 Kelly drilling rigs. In addition, we used MAT mixing plants to produce the 35 different specialized grout mixes that were developed for the different soil conditions along the 10 miles of cut-off wall. All the drilling equipment, as well as the mixing equipment, was made by our sister company, Bauer BMA, located in Schrobenhausen, Germany.”
A slag cement-based grout was used for the majority of the project in addition to a percentage of bentonite. Over half a million cubic yards was needed to produce the cutoff wall.
Hansen said numerous piping conditions existed.
“This piping condition created weak sections of the dike. During CSM operations, the hole is never left open because of the mix in place aspect of this process. Also, during the pre-drilling process, we used a cased method which reduced the possibility of a dike failure as we drilled through these areas. The steel casing was advanced with the drilling operation and worked as a barrier to keep the piping from affecting our operations. This combination of mix in place wall placement and cased holes meant that there was never an open excavation in contact with a piping condition.”
According to Hansen, lightning was responsible for the most work interruptions. In addition, tropical storms shut down operations at least once.
“In both cases, we worked double shifts in order to make up the time, and neither of these weather conditions ended up delaying the project,” said Hanson. “We were also affected by the presence of an osprey. It nested near our work area and we could not continue until the family of osprey left.”
The first embankments around Lake Okeechobee were reportedly constructed around 1915. Hurricane tides overtopped the original embankments in 1926 and 1928, claiming more than 2,500 lives. The River and Harbor Act of 1930 authorized the construction of approximately 70 mi. (112.7 km) of levee along the south shore of the lake and roughly 16 mi. (25.7 km) along the north shore. The U. S. Army Corps of Engineers constructed the levees between 1932 and 1938.
A major hurricane in 1947 led to additional flood and storm damage reduction work. Congress passed the Flood Control Act of 1948, approving the first phase of a project designed to provide flood and storm damage reduction in central and south Florida. The current dike system was completed in the late 1960s. The dam was originally constructed with gravel, rock, limestone, shell and sand.
Campbell said recent wet weather has made the project even more challenging.
“Summer rains caused the lake to rise about two feet in the span of three months. The concern about a rising lake so early in the summer is the reduction in available capacity to handle major rain-producing events, such as tropical storms and hurricanes. In 2011 and 2012, the lake rose three feet in about a month. If such an event were to happen today, the resulting lake rise would put us well past 18 and a half feet where the lake is estimated to have a 50-50 chance of failure without any intervention at some point on the dike.”
USACE officials are well aware of public concern over the aging dike. Nearby residents are understandably concerned, but Campbell said there’s no need to panic at this point.
“We will address any issues that come up to ensure the safety of the people living and working around the lake. We would encourage them to be aware of the risks, and know how to get information from their local officials who would order an evacuation in a worst-case scenario.”
While Campbell stressed there’s no imminent threat of failure, the situation is far from being resolved.
“Our concern is what a heavy rain-producing event would do to the lake, and how quickly it might rise before we can release enough water to lower,” said Campbell. “One of the major problems with water management at the lake is that the inflows from runoff can exceed by a factor of six our ability to send the water elsewhere under the current drainage system. That’s why we manage the lake lower than in the past, to be able to handle a heavy-rain event that causes a three-foot rise in a span of four weeks.”
Of the 32 culverts, USACE plans to replace 28 of them, and seal-off three that are abandoned.
“We’ve already removed one culvert,” said Campbell. “These are much larger than structures that run under a drive. They are large enough to convey water to area farms fields, but too small to have any meaningful impact on managing lake levels.”
USACE also removed foliage that can weaken the dike, and stockpiled rock at strategic spots. Stockpiling helps prepare for a breach scenario by ensuring materials on hand, as opposed to having to wait for those materials to be shipped from a quarry.
In 2000, the Corps produced a report that included probabilities of failure without any intervention. The report indicated when the lake reached elevation 18.5 ft. (5.6 m), the probability of failure at a single point on the dike was 45 percent.
“The chances of failure increased with higher elevations to include near certain failure as the lake approached elevation 21 feet,” said Campbell. “Those probabilities were determined ’without intervention’, which assumes no one executed any emergency response to address issues in the short-term, and that no action was taken to fix the dike over the long-term. We have demonstrated a commitment to respond to any emergency situations since this report was prepared, and we have also demonstrated a commitment to the tune of $750 million invested in dike repairs since 2001.”
The U.S. Army Corps of Engineers authorized a dam safety modification study on Herbert Hoover Dike, in addition to pumping millions of dollars into the project. Corps teams work daily on the dike, providing contractor oversight, inspections and dike operations and maintenance. Various engineers, geologists and hydrologists are providing input.
The USACE Jacksonville District awarded its third contract in a month to replace two additional water control structures in the dike as part of the rehabilitation project. In September 2013, the corps awarded a $36 million contract to Harry Pepper & Associates of Jacksonville. The contract calls for replacement of Culvert 8 near Okeechobee along the north side of the lake and Culvert 13 near Canal Point in Palm Beach County. The water control structures provide irrigation and drainage to landowners in the area. This work on the project is expected to be complete by the spring of 2017.
“The Corps clearly believes this is a very critical project,” said Campbell. “When all is said and done, we will have likely invested more than $1 billion in repairs to the earthen embankment and associated structures to reduce the risk the dike will fail.”
Today's top stories
