Corps working on flexible plan to manage Lake O

Posted 4/18/21

The manmade drainage system that sends water into Lake Okeechobee much faster than it can be released continues to create challenges for water managers.

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Corps working on flexible plan to manage Lake O

Posted

The manmade drainage system that sends water into Lake Okeechobee much faster than it can be released continues to create challenges for water managers.

Water flows into Lake Okeechobee much faster than it can be released, Savannah Lacy, Lake Okeechobee water manager with the U.S. Army Corps of Engineers, explained during an April 14 media tour of the Herbert Hoover Dike.

On average, about 732 billion gallons of water flows into the Big O from from the northern watershed that starts just south of Orlando. That is the equivalent of about 5 feet of water on Lake Okeechobee. Another 548 billion gallons – about 3.77 feet of water on the lake – comes from direct rainfall into the lake.

Most of the water that leaves the lake does so through evapotranspiration (the combination of evaporation into the air and transpiration by plants) and percolation into the aquifer. About 727 billion gallons of water leaves the lake this way.

About 225 billion gallons of water from the lake flows south each year. Some of this water is used for agricultural irrigation and urban water supply. Some water flows to Everglades National Park.

That leaves about 328 billion gallons of water.

The Caloosahatchee River needs some freshwater flow from the lake during the dry season to prevent the salinity levels in the estuaries from getting too high. Different parts of the estuaries have different optimal salinity levels. On average, scientists who study the river recommend a flow of about 1,000 cubic feet per second (cfs) to the river during the dry season. That’s about 538 million gallons per day or about 98 billion gallons for the six months of the dry season.

That leaves about 230 billion gallons of water – about 19 inches of water on the Big O. Just what happens to that water is the question to be answered with the new Lake Okeechobee System Operating Manual (LOSOM).

Under the Lake Okeechobee Regulation Schedule (LORS) which was established in 2008, that excess water is sent east and west to tide with about 95 billion gallons going east through the Port Mayaca Lock and the rest released at Moore Haven to the Caloosahatchee River. These freshwater discharges can lower the salinity in the estuaries, which harms the ecosystems and makes them more vulnerable to harmful algal blooms.

Note: “Average” years are rare. Some years are very wet. In other years, the system may be in drought. One goal of LOSOM is to create the flexibility in the schedule to continually adapt the plan to whatever Mother Nature sends.

Water storage projects are under construction east and west of the lake, and south of the lake, construction is expected to start on the EAA reservoir later this year. Reservoirs near the Caloosahatchee River and St. Lucie Canal may be used to store some of the excess lake water rather than send it to tide. The Everglades Agricultural Area (EAA) reservoir south of the lake, may increase capacity to send more water south. How much capacity these reservoirs will have in the wet season will in part depend on how much they are filled by direct rainfall.

In an effort to expedite water storage north of the lake, over the past two years the Florida State Legislature has allocated $100 million to “jump start” the Lake Okeechobee Watershed Restoration Plan (LOWRP) which include 80 aquifer storage and recovery (ASR) wells. The ASR portion of LOWRP is expected to cost about $400 million. On April 7, Florida Senate unanimously passed Senate Bill 2516, Water Storage North of Lake Okeechobee, which would provide more funding for LOWRP.

The 80 ASR wells planned in LOWRP could provide an annual 448,000 acre feet of storage – that’s room for about 146 billion gallons of water per year. While the ASRs don’t completely eliminate the need for coastal discharges, that extra storage capacity could help not only reduce the discharges but also provide backup water supply in dry years.

Due to the capacity of a hurricane to rapidly cause the lake to rise, no plan can completely eliminate the potential for coastal releases, but combined with the Comprehensive Everglades Restoration Plan (CERP) projects, the reservoirs north, south, east and west of the lake are expected to significantly reduce both the frequency and the volume of harmful coastal discharges.

“In recent years, Florida’s Legislature has appropriated unprecedented funding to address environmental restoration. Collaborative efforts between the state and federal government successfully expedited the beginning phases of construction of the Everglades Agricultural Area Reservoir south of Lake Okeechobee. Now it is time to build on this momentum by focusing on projects north of the lake,” said Senate President Wilton Simpson (R-Trilby). “I am grateful to my Senate colleagues for approaching solutions north of the lake with the same vigor we had for southern storage. Implementation of the LOWRP is the most important element of restoration for the northern Everglades ecosystem, as approximately 95 percent of the water, 92 percent of the phosphorus, and 89 percent of the nitrogen flowing into Lake Okeechobee comes from north of the lake.”

SB 2516 requires the SFWMD to request that the USACE seek expedited congressional approval of the LOWRP and execute a project partnership agreement with the USACE immediately following approval. The bill also requires expedited implementation of the aquifer storage and recovery (ASR) Science Plan developed by the SFWMD and the USACE, and expedited implementation of the watershed ASR feature of the LOWRP.

The bill amends section 375.041, Florida Statutes, to provide a $50 million annual appropriation from the Land Acquisition Trust Fund to the SFWMD for the LOWRP. $100 million has been appropriated for the LOWRP over the past two fiscal years.

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