Water Releases 101: LORS
There has been a lot of information in the news lately about how excess water releases from Lake Okeechobee are the reason why the water on our beaches is smelly and brown. Fresh water laden with excessive nitrogen and phosphorous from the lake and runoff from farms and cities along the river has been pouring into our sensitive estuaries at a rate much higher than normal. But who decides to release that water and why? While many of our readers are aware that it is the Army Corps of Engineers who have the power to open or shut the gates at the Caloosahatchee River's Moore Haven Lock on the lake's western shore, there has been little information as to what guides them in their decisions. The truth is that most of these decisions are made based on guidelines called the Lake Okeechobee Water Release Schedule, or LORS, which was most recently updated in 2008.
"Following devastating hurricanes in the 1920s, Congress authorized construction of Herbert Hoover Dike around Lake Okeechobee,” said Col. Alan Dodd, Commanding Officer of the Jacksonville District of the Army Corps of Engineers. "Then, after hurricanes in the 1940s, Congress authorized the Central & Southern Florida Project to move water via levees and canals for flood protection. In the last decade, we revised the master water control plan to ease the strain on the aging dike and to address massive water releases following major hurricanes in 2004 and 2005. Our rigorous process incorporated input from many perspectives, including government, environmental groups, agriculture and the public. The 2008 Lake Okeechobee Regulation Schedule resulted. Under the schedule, we and our state water management partners strive to maintain a lake level between 12½ and 15½ feet, reducing the threat of a potential dike failure.” Previous water control plans allowed water levels to reach 17 or 18 feet before any action was taken, which has caused erosion and internal seepage.
Dodd told us that the LORS is driven by three primary factors: current lake level, inflow from the watershed and short- and long-term precipitation forecast.
"We consider public safety, the environment and other authorized uses of the lake in our decisions,” he said "We recognize our decisions have a multitude of consequences on these competing needs, and we continually seek balance.”
The 2008 LORS Flow Chart looks complicated at first glance but is actually relatively simple. Staring with the current level of the lake, engineers determine if that level falls into one of five Sub-Bands which then lead to what the current conditions are and the upcoming 30-day weather forecast to a set of thirteen possible outcomes of how much water to release to the estuaries (Caloosahatchee and St. Lucie Rivers). A similar flow chart dictates what should be released south to the Water Conservation Areas (WCA').
"Last August, after Hurricane Isaac passed over the state, water levels in Lake O rose three and half feet in six weeks, causing the levels to raise rapidly into the higher Sub-Bands,” said John Campbell, Public Affairs Specialist for the Jacksonville District, who gave us slides marked to show how the flow chart works, accompanied by a chart depicting lake levels over the past year. "I call attention to the levels on May 8 when we started releases. Note the rising levels from the Low to Intermediate and High Sub-Bands, even as we increased discharges as we passed through each level.”
(PIC Lake O Water Levels)
Campbell explained how the decision was made on July 20th to increase water releases based on the levels passing into those Sub-Bands and to make even larger releases on July 25th as the lake continued to rise.
"The second slide shows the LORS decision tree when we announced an increase in water releases on July 20,” he said. "At that point, we had passed into the Intermediate Sub-Band, with the lake projected to rise into High Sub-Band. The release decision was 6,500 cfs (cubic feet per second) through Moore Haven Lock and 2,800 cfs through St. Lucie. The third slide shows the LORS decision tree when we announced maximum flows on July 25. The lake had entered High Sub-Band, and was projected to rise into High Lake Management Band.”
John told us that the High Lake Management Band occurs when the lake reaches a level of 17.25 feet, something that hasn't happened yet.
"We did briefly reach the High Sub-Band, which - depending on the time of year - occurs when lake levels reach 15.5 feet to 16.75 feet,” he said. "The bands are seasonally adjusted as we like to keep the lake lower in June because there are still several months of rainy season and higher in November in anticipation of the dry season.”
Campbell said that since that decision was made on July 25th, lake levels have dropped rapidly, resulting in the Corps lowering releases from the Moore Haven Lock (S-77) to 4,000 cfs - Low Sub-Band - on Saturday morning. That schedule remains the same as of press time. However, flows from the Franklin Lock (S-79) were at 9,680cfs - meaning that more water is coming down the river from Caloosahatchee Watershed runoff than from the lake itself.
"As you can see from all the decision-tree slides, if 'tributary hydrological conditions' (i.e. inflows to the lake) return to 'wet' or 'normal' additional decreases in flows could be possible,” Campbell told us. "However, we still have concerns for the relatively high lake level for this time of year. Should flows increase again, due to heavy rain or a tropical event, we would use the LORS decision-tree to provide guidance for increasing the releases as necessary. The Corps will closely monitor conditions and adjust flows as necessary to balance the competing needs and purposes of Lake Okeechobee. Public safety remains the Corps' top priority.”
During a teleconference last week, we asked Lieutenant Colonel Thomas M. Greco - Deputy Commander for Jacksonville - when and if the Corps expects to see an updated version LORS, and he told us that the schedule will not be revised until ongoing improvement projects to the Herbert Hoover Dike are completed. At an special hearing of the state legislature held last week in Stuart, Senator Joe Negron said he wants an assessment by experts from the state and corps to make sure the release schedule is based on the latest evidence, balancing the risk of breach against damage to the environment. Keri Hendry Weeg