JACKSONVILLE – The U.S. Army Corps of Engineers continues to fine tune the Lake Okeechobee System Operating Manual (LOSOM), which will be used to manage the big lake when repairs to the Herbert Hoover Dike are complete later this year,

USACE invites public comment on LOSOM during a Listening Session online, on Monday, March 21, from 1 to 4 p.m.

At the March 7 LOSOM Project Delivery Team (PDT) meeting, Savannah Lacy, hydraulic engineer with the U.S. Army Corps of Engineers, explained the lake’s ecology needs periods of low water. Low lake levels allow the marshy areas around the edge of the lake to dry out, for sunlight to reach the lake bottom and submerged aquatic vegetation (SAV) to sprout and grow.

The SAV and marshes provide critical habitat for fish and wildlife. The plants also help clean the lake water, removing phosphorus and nitrogen.

The SAV needs at least 30 days with the lake below 13 feet to become established, and when the lake starts to rise, the rate of rise is also important. If the water rises faster than the plants grow, the plants can be damaged or die.

Nature intended the lake to rise very slowly throughout the wet season. Before flood control, according to the U.S. Geological Survey, water that fell at the top of the system near Kissimmee took six months to slowly sheetflow south to Lake O. As it slowly sheetflowed, the water was cleaned by vegetation, and some of the flow evaporated into the air and percolated into the earth, recharging the aquifer. The canals, channelization of the Kissimmee River and other flood control measures changed that. Water that falls at the top of the watershed now takes just a few weeks to reach the big lake. The faster flow also means the water does not have time to be cleaned by vegetation.

At the PDT meeting, Lacy explained LOSOM may include mitigation strategies to help the lake recover from high lake levels due to periods of heavy rainfall north of the Big O. Such a mitigation would attempt to draw down the lake to 12.5 feet above sea level in June.

The intent is to find synergy between:
• Mitigating prolonged moderately high lake stages for lake ecology; and,
• Reducing the risk of high volume releases to the estuaries in the summer after adverse conditions in previous year due to high releases or harmful algal blooms.

“When the northern estuaries go through a high flow situation in one year, it’s really beneficial for them to get some kind of recovery period, some kind of rest,” said Lacy.

“We would not do this every year. It would be triggered,” she explained. “It would not be part of the every day regulation schedule.”

The intent is to mitigate prolonged moderately high stages, she said.

When the lake doesn’t get down below 13 feet during the dry season, it can be really harmful to the ecology, she explained.

Proposed triggers might include:
• If lake stages do not recede below 14 feet in a given year;
• If lake stages do not recede below 13 feet at least once in two years;
• If lake stages during the wet season exceed 15 feet for more long periods of time;
• Ecological indicators on Lake Okeechobee to possibly include SAV coverage or large mouth bass population;
• Multiple estuary damaging events; or,
• Harmful algal blooms in the northern estuaries.

She said the drawn down in 2019 helped the system reset.

The draw down would be a moderate draw down to 12.5 feet before the beginning of the wet season. It might not be the year immediately following a high water level year, she explained.

“Going from 17 to 11 is pretty drastic,” she said. Due to Hurricane Irma, Lake Okeechobee rose to 17 feet in 2017. The corps initiated a draw down not the next spring, but the following spring of 2019.

USACE will have a LOSOM Listening Session online, on Monday, March 21, from 1 to 4 p.m,
To participate,
• Go online to https://usace1.webex.com/meet/earl.t.gysan or,
• Call-in toll-free number (ATT Audio Conference):1-844-800-2712
• Call-in number (ATT Audio Conference):1-669-234-1177
Access Code: 1997788788.