JACKSONVILLE — The U.S. Army Corps of Engineers (USACE) Jacksonville District plans to execute a two-day deviation Dec. 14-15 that will release water from the lake as part of an ongoing sediment study by the South Florida Water Management District (SFWMD) and the U.S. Geological Survey (USGS).
The releases will affect both the Julian Keen Lock and Dam (S-77) and the Port Mayaca Lock and Dam (S-308) as short bursts of water are released to support the study.
The initial releases are planned for Dec. 14 at S-77 and are expected to last for a maximum of four hours of flows not to exceed 1,000 cubic feet per second, followed by additional flows not to exceed 2,000 cfs for a maximum of four hours. The following day, flows at S-308 will not exceed 1,000 cfs for a maximum of four hours.
The purpose of study is to better understand nutrient and sediment transport to the estuaries under different flow conditions. USACE executed a similar deviation in December to support the same study.
The releases are expected to be executed for short durations up to the maximums allowed in the deviation, but researchers expect the daily average flows will be significantly lower than the maximum allowed in the deviation. To ensure there is enough time, the study was approved for eight hours on Dec. 14 and four hours on Dec. 15, but is expected to be completed in much less time. Actual duration is more likely to be shorter.
USACE will prepare the C-44 canal for the study by letting the canal levels recede below normal operating levels to minimum canal levels for navigation on the day before the event, reducing the potential for the study to require opening the St. Lucie Lock and Dam (S-80) during or immediately following the study. USACE does not anticipate the releases from S-77 will result in exceeding the seven-day 2,000 cfs target for releases to the Caloosahatchee River Estuary out of S-79. As is always the case, heavier than normal rainfall could result in flows exceeding the targets at both S-79 and S-80.
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.