JACKSONVILLE — The U.S. Army Corps of Engineers will start freshwater releases from Lake Okeechobee to the Caloosahatchee River on Saturday, Oct. 5, to help maintain healthy salinity levels in the estuaries. The driest September since record keeping started in 1932 has left the Caloosahatchee basin short of water, requiring the lake releases.
“The runoff that usually feeds the estuaries has run out,” said Col. Andrew Kelly, USACOE Jacksonville District commander, during an Oct. 4 media conference call. Target releases to the Caloosahatchee estuaries, measured at the Franklin Lock, will start at an average 650 cubic feet per second on Oct. 5. That equals about 420 million gallons of water per day. One inch on Lake Okeechobee is about 12 billion gallons, so at that rate the releases would lower the lake by about one inch per month, he explained.
“Until recently, the Caloosahatchee estuary had been getting enough basin runoff to meet or exceed the 650 cfs base flow target at W. P. Franklin. Now that the basin is not providing the runoff to meet this target, the corps will release lake water to supplement flows,” said Col. Kelly.
The South Florida Water Management District has set the minimum flow at the Franklin Lock at 450 cfs. Col. Kelly said the decision to release lake water to maintain a flow of 650 cfs is based on the needs of the river and the salinity levels in the estuaries.
Col. Kelly said this was a tough decision because the lake is already lower than average for this time of year. The lake level on Friday was 13.49 feet above sea level. On Oct. 4, 2018, the lake was 14.42 feet. The average lake level Oct. 4, based on data from 1965 to 2007, is 14.93 feet.
“We still have about a month left in the wet season,” said Col. Kelly. “I’m not convinced we’re in the dry season yet.”
Col. Kelly said if the lake level continues to fall, he will re-evaluate conditions and could reduce flow to the Caloosahatchee River.
Over the past year, the corps used the “operational flexibility” in the Lake Okeechobee Regulation Schedule to get the lake below 11 feet above sea level by the start of the dry season, to help restore the lake’s submerged aquatic vegetation (SAV), which was devastated by the winds during and high water level following Hurricane Irma in 2017.
Col. Kelly said they have seen water quality improvements in the lake over the summer. “We’ve definitely seen improvement in water clarity,” he said. “We’ve seen additional SAV growth. We don’t yet understand how resilient those grasses are going forward.”
Col. Kelly said if they reduce flows from the lake to the Caloosahatchee in coming weeks, “it’s not all or nothing. We will do the best we can to ramp down releases until we feel we couldn’t release anything.”
Most of the “operational flexibility” was used to maintain optimal freshwater flows of 800 to 1,000 cfs to the Caloosahatchee River during the 2018-2019 dry season. Additional flows to “lower the lake” made to the Caloosahatchee River and the St. Lucie canal over a six-week period in February and March accounted for about 2 inches on the Big O.
Total “operational flexibility” releases lowered the lake by about 1 foot.
Col. Kelly said water managers use the best information available to predict rainfall. If Hurricane Dorian had come across Florida, the situation would be much different now, he added.
“Most of the time, Mother Nature’s in charge,” he said.