The U.S. Army Corps of Engineers (USACE) Jacksonville District plans to execute a minor adjustment to the current lake release schedule from Tuesday, February 21 through Friday, February 24, that will release water from Lake Okeechobee as part of an ongoing sediment study by the South Florida Water Management District (SFWMD) and the U.S. Geological Survey (USGS).

The current lake release target has been in effect since January 20, 2023. Releases from Lake Okeechobee are scheduled at a seven-day average pulse release of 2,000 cubic feet per second to the Caloosahatchee Estuary at the W.P. Franklin Lock and Dam (S-79) and a seven-day average pulse release of 500 cubic feet per second to the St. Lucie Estuary at the St. Lucie Lock and Dam (S-80). In addition, there is a seven-day steady release of 100 cubic feet per second to the Lake Worth Lagoon from Lake Okeechobee.

The releases for the upcoming sediment study will affect only the Port Mayaca Lock and Dam (S-308) and the Julian Keen, Jr. Lock and Dam (S-77) as water is released to support the study.

The initial study releases are planned for the morning of Tuesday, February 21 at the Port Mayaca Lock and Dam (S-308) and are expected to last for a maximum of four hours of flows not to exceed 2,800 cubic feet per second, followed by flows not to exceed 1,500 cubic feet per second in the afternoon, for a maximum of four hours. On Wednesday, February 22, study releases are expected to last for a maximum of four hours of flows not to exceed 2,400 cubic feet per second, followed by flows not to exceed 1,500 cubic feet per second in the afternoon, for a maximum of four hours.

The estimated total volume for the releases via S-308 is approximately 2,700 acre-feet, which is the equivalent of 0.004 feet, less than a tenth of an inch on the lake.

Lock and dam operators at Port Mayaca Lock and Dam and the St. Lucie Lock and Dam will coordinate operations so that study releases will not affect the current lake release schedule of an average of 500 cubic feet per second at the St. Lucie Lock and Dam (S-80) to the extent possible.

During the collection period, the S-77 is required to be open to take sediment measurements. This deviation allows the USACE to open S-77 for a relatively short period of time, even though flows at S-79 will be above the flow target of 0 cubic feet per second.

Study releases are planned for the morning of Thursday, February 23, at the Julian Keen Jr. Lock and Dam (S-77) and are expected to last for a maximum of four hours of flows not to exceed 3,600 cubic feet per second, followed by flows not to exceed 1,500 cubic feet per second in the afternoon, for a maximum of four hours. On Friday, February 22, study releases are expected to last for a maximum of four hours of flows not to exceed 3,000 cubic feet per second, followed by flows not to exceed 1,500 cubic feet per second in the afternoon, for a maximum of four hours.

The estimated total volume for the releases via S-77 is 3,200 acre-feet, which is the equivalent of 0.005 feet, less than a tenth of an inch on the lake.

No downstream impacts are expected in the Caloosahatchee River Estuary due to the short duration of the study.

The purpose of study is to better understand nutrient and sediment transport to the estuaries under different flow conditions. USACE executed similar deviations in 2021 and 2022 to support the same study.

This important research will help understand the relationship between suspended sediment concentrations, how they originate, how they carry nutrients, and how that might impact algal bloom development and growth.

USACE will monitor conditions and work with USGS and SFWMD to adjust flows for these studies as necessary if conditions on the lake or in the estuaries change.