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The Battle to Draw Down Lake Okeechobee

By: Dr. Jeff Masters, 2:39 PM GMT on August 24, 2013

After the wettest July ever recorded in Florida, the Army Corps of Engineers is battling to draw down the level of Lake Okeechobee before the September peak of the rainy season. The huge lake represents an important source of fresh water to South Florida, but also poses a grave danger. The 25 - 30'-tall, 143-mile long Herbert Hoover Dike surrounding the lake was built in the 1930s out of gravel, rock, limestone, sand, and shell using old engineering methods. The dike is tall enough that it cannot be overtopped by a storm surge from anything but an extreme hurricane, but the dike is vulnerable to leaking and failure when heavy rains bring high water levels to the lake. The Army Corps of Engineers is scrambling to complete a $300 million upgrade to the dike to reduce the chances of such a failure. However, those repairs are not scheduled to be completed until 2018, and the Corps is warning that the Lake Okeechobee dike is in danger of failure this year should heavy rains from a tropical storm or hurricane raise the lake level and put high stresses on the old dike. A 2011 risk assessment estimated the dike's probable failure rate at every fourteen years. A 2008 Army Corp of Engineers study said this about the vulnerable dike:

"There is limited potential for a dike failure with lake levels as low as 18.5 feet. The likelihood of a failure increases at higher lake levels. At a lake level of 21 feet--a 1-in-100 year flood event--a dike failure would be likely at one or more locations. In the event of a dike failure, waters from Lake Okeechobee would pass through the breach--uncontrollably--and flood adjacent land. Flooding would be severe and warning time would be limited. And with 40,000 people living in the communities protected by the Herbert Hoover Dike, the potential for human suffering and loss of life is significant. Our engineering studies indicate the southern and eastern portions of the dike system are more likely to fail than the northern and western portions of the dike. In general, we would expect a warning time of 24 to 48 hours prior to a dike failure that releases water from the lake; however, under some conditions the warning time might be longer, and under others, a dike failure could occur with no warning."

The city most at risk from a dike failure may be Belle Glade (population 18,000) on the southeast shore. Belle Glade is at 16' elevation. If Lake Okeechobee is at 20' above mean sea level when the dike fails, this implies that at least three feet of water could flood Belle Glade. If a wide section of the dike breaks and there is a Cat 3+ hurricane driving a massive storm surge at the time, then the flood could be much higher. During the 1928 hurricane, which had 130 mph winds while over the lake, the water from the storm surge reached seven feet above ground level in Belle Glade.

Figure 1. Water level of Florida's Lake Okeechobee between January 2012 and August 23, 2013. The SFWMD reported that 2013 had the wettest start to the annual wet season in 45 years, with the district-wide average rainfall for July at 10.36". Heavy rains from Tropical Storm Isaac in late August of 2012 caused a 3.5' rise in lake water levels in six weeks; record rains in July 2013 caused a 3' rise in water levels to 16' in mid-August, just below the record high lake level for that time of year. The Army Corps tries to keep the lake level below 15.5'; the dike surrounding the lake is in danger of failure when the lake level hits 18.5'. As of August 23, 2013, the lake level was 15.6', after hitting a peak of 16.1' early in August. Lake Okeechobee reached an elevation of 18.6' and 18.5'--both 1-in-30-year events--in 1995 and 1998. Image credit: Army Corps of Engineers.

Figure 2. Aftermath of the 1928 Okeechobee Hurricane, showing damage to a cluster of Everglades scientific work stations in Belle Glade. The hurricane killed 2,500 people, mostly near Belle Glade. Image credit: University of Florida, via the historicpalmbeach.com.

The Great 1928 Lake Okeechobee Hurricane
The shores of Lake Okeechobee are the site of the second deadliest natural disaster in U.S. history--the 1928 Okeechobee Hurricane. This mighty hurricane caused catastrophic damage where it struck the Florida coast as a Category 4 storm near Palm Beach, and weakened only slightly to Category 3 strength with 130 mph winds when it passed over Lake Okeechobee. The powerful winds of the hurricane brought a 12' storm surge to the south end of the lake, which overwhelmed the 6' high levees protecting the farm lands to the south. The resulting flood covered an area of hundreds of square miles with water up to 20' deep, and killed at least 2,500 people--mostly black migrant farm workers. A mass grave at the Port Mayaca Cemetery east of Port Mayaca contains the bodies of 1,600 victims of the hurricane. The Herbert Hoover Dike was built in the 1930s around most of Lake Okeechobee in response to this disaster.

Figure 3. When Lake Okeechobee water levels exceed 15.5' above mean sea level, large amounts of lake water are released out of two canals that carry the storm water runoff to the ocean. The western drainage canal flows into the Caloosahtchee Estuary and into the Gulf of Mexico at Fort Myers. The eastern drainage canal flows into the St. Lucie River Estuary and into the Atlantic Ocean near Stuart. High levels of nutrients due to agricultural runoff in the Lake Okeechobee water have been causing toxic algae blooms in the areas marked in green during July and August of 2013.

Lake Okeechobee runoff contributing to toxic algae blooms
Heavy rains that began in early July raised the level of Lake Okeechobee by two feet, to sixteen feet. Torrential rains of 7+ inches from a tropical storm or hurricane are capable of raising the lake level by over three feet in a few weeks; this occurred in 2008, when Tropical Storm Fay took a leisurely romp across Florida, and again in 2012, when Tropical Storm Isaac lumbered past. Under ideal conditions, the Army Corps can only lower the lake at a rate of about 0.4" per day. The Corps has been dumping water out of the lake since May 9, and began dumping water out as fast as it could beginning on July 25, to keep the lake below 15.5'. Had these releases not occurred, the lake would have been two feet higher than it is now. Most of this excess water was sent out Lake Okeechobee's western drainage canal into the Caloosahtchee Estuary, which empties into the Gulf of Mexico at Fort Myers. The Lake Okeechobee water is full of agricultural runoff and laden with fertilizers, and this polluted water, combined with an even greater amount of polluted water coming from local runoff due to heavy rains, caused a toxic red tide bloom in the coastal waters of Fort Myers that is being blamed for a record 133 manatees deaths this year. A lesser amount of Lake Okeechobee water has been sent eastwards into the St. Lucie River, where it drains into the Atlantic Ocean near Stuart through the Indian River Lagoon. A similar level of discharge goes down the C-51 canal in into the estuary by West Palm Beach, the Lake Worth Lagoon. The polluted Lake Okeechobee water, which was also combined with large amounts of polluted local runoff water from heavy rains, has caused havoc in these coastal waters this summer, affecting oyster beds, sea grasses, mangroves, and wildlife. Numerous toxic algae blooms have created lime-green water unsafe for recreation in the Indian River Lagoon, leading to calls by local residents for immediate political action. Temporary relief is at hand, though. On Wednesday, the Corps announced that due to falling lake levels, an easing up of the summer rains, and a forecast for merely average rains over the next week, water releases from then lake would be cut almost in half. A further reduction in flow began on Saturday morning. Governor Rick Scott of Florida announced this week that the state of Florida was committing $40 million to a project to build a reservoir aimed at diverting storm water releases from Lake Okeechobee. However, a press release by a coalition of environmental groups labeled this solution as a "Band-aid", saying "It only addresses a tiny fraction of the sewage, manure, and fertilizer runoff--called ‘nutrient pollution’--that comes from within the St. Lucie watershed, and it does nothing to reduce the nutrient pollution sliming all the other, rivers, springs, lakes and bays all over Florida.”

Figure 4. A toxic algae bloom in the St. Lucie River in Stuart, FL on August 1, 2013. Image credit: Dick Miller.

Figure 5. This photo taken from Martin County Sheriffs Office Air 1 shows thousands of people spelling out “Save Our River” along the Florida shoreline from Stuart to Jensen Beach on August 11, 2013. The people were protesting water pollution due to storm water runoff from Lake Okeechobee and local sources that has caused toxic algae blooms. Source: Martin County Sheriffs Office, via the Martin County Times.

For further reading
Despite repairs, Lake Okeechobee dike remains a danger: August 16, 2013 Miami Herald article.

Jeff Masters

Hurricane Air and Water Pollution

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.