LAKE OKEECHOBEE – While releases from Lake Okeechobee to the coastal estuaries get a lot of attention in the news, the Big O is just one source of water entering the St. Lucie and Caloosahatchee Rivers.
At a media briefing on April 14, Andrew LoSchiavo, U.S. Army Corps of Engineers lead biologist, explained “Lake Okeechobee water is just one source of water going to the estuaries.”
He said looking at the average Water Years 1997 through 2017, water from Lake Okeechobee made up just 20% of the freshwater flow to the St. Lucie River. C-44 Basin runoff accounted for nearly half the flow – 49.9%. Tidal basin runoff was 30.1% of the flow.
Lake water enters the C-44 canal (the St. Lucie Canal) at Port Mayaca, which is 23.9 miles from the St. Lucie Lock. When lake water is released into the canal at Port Mayaca, that water mixes with local basin runoff that drains into the canal.
On the west side of the state, for that same period, water from Lake Okeechobee was 25.5% of the flow to the Caloosahatchee River. C-43 basin flow (which drains directly into the river) accounted for 26.2% of the flow. The remaining 49.9% came from the tidal basin. The Franklin Lock, where flow of the river is measured entering the estuaries, is 43.4 miles from the Moore Haven Lock.
A “water year” runs from May 1 to April 30.
Projects included in the Comprehensive Everglades Restoration Plan (CERP) are designed to send more water from Lake Okeechobee south, explained Michael Hensch, one of the lead water managers for the corps.
How much water can be sent south depends on a number of factors including direct rainfall to that area. In 2020, Hurricane Eta dropped so much water south of Lake Okeechobee, the water conservation areas were flooded.
Hensch said Water Conservation Area 3 (WCA-3) is about the size of Lake Okeechobee. Habitat for wildlife native to this area of the Everglades is lost if the water levels get too high. He said one of the goals of the Combined Operation Plan (COP) is to move more water out of WCA-3 and under the Tamiami Trail to Everglades National Park.
South of the trail, one of the constraints to sending water south is the Cape Sable Seaside Sparrow, Hensch continued. For nine months of the year, U.S. Fish and Wildlife Service requires some of the water control structures be closed to protect the nesting grounds of subpopulation A of the sparrows.
The Tamiami Trail blocks the natural flow of water. He said Florida Department of Transportation requires them to keep the L-29 canal which runs along the trail, below 8.5 feet most of the year, limiting levels above 8.5 feet to no more than 90 days. “This year, FDOT allows us to go to 150 days,” he explained. As the corps is sending more water south, “we’re moving more and more water through the L-29,” he explained.
He said the new 2.6 mile bridge and the 1 mile bridge on the Tamiami Trail have improved the capacity to send water under the Tamiami Trail.
Another constraint to moving water south is the Las Palmas development, also called the 8.5 square mile area. These homes are in an area west of the East Coast Protection Levee and next door to Everglades National Park. “As we send more water to Shark River Slough, it increases seepage in the 8.5 square mile area,” he explained. The two conveyance canals in the 8.5 square mile area cannot keep up with the flow. The South Florida Water Management District recently approved construction of an underground curtain wall to keep water in Everglades National Park from seeping into the 8.5 square mile area.
Despite the constraints, flow to Everglades National Park is improving. In 2020, the corps sent over 1.56 million acre feet of water under the Tamiami Trail to Everglades National Park.
Water deliveries under the Tamiami Trail were:
• 2012: 804,000 acre feet;
• 2013: 818,300 ace feet;
• 2014: 571,800 acre feet;
In the first three months of 2021, 494,880 acre feet of water moved through the water control structures under the trail to Everglades National Park.