Computer models seek the best plan for Lake Okeechobee management

Posted 11/21/20

What’s the best plan for outflows from Lake Okeechobee, to the east, west and south?

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Computer models seek the best plan for Lake Okeechobee management


JACKSONVILLE — What’s the best plan for outflows from Lake Okeechobee, to the east, west and south? How low should the lake go before the start of the dry season? How high should it rise in the wet season?

The U.S. Army Corps of Engineers and the South Florida Water Management District are working on a new plan to manage the lake, which will go into effect when repairs to the Herbert Hoover Dike are complete in 2022.

At the Lake Okeechobee System Operating Manual (LOSOM) Project Delivery Team online meeting on Nov. 20, corps officials reviewed the project objectives and the results of 120,000 computer model runs.

“We have completed development of conceptual plans,” explained Lisa Aley of the U.S. Army Corps of Engineers. “We have the model results of 120,000 runs. We are sifting through the plans for each project objective.

“We want to make sure we aren’t too conservative up front and leave any benefits on the table,” she added.

There will be some schedules that perform extremely well for some objectives and very poorly for others, she explained. “We’ll use what we learn from these schedules to develop a balanced plan.”

Of those 120,000 runs, about 117,000 passed the dam safety check and about 27,000 plans are Pareto optimal. (The Pareto Principle, named after economist Vilfredo Pareto, specifies that 80% of consequences come from 20% of the causes, asserting an unequal relationship between inputs and outputs. This principle serves as a reminder that the relationship between inputs and outputs is not balanced.)

Savannah Lacy, Lake Okeechobee water manager for the corps, said some of the conceptual schedules are based on a single goal. Water managers developed conceptual schedules for each sub-objective.

The modeling team took those concepts and created many variations on those conceptual schedules.

Objectives of the plan are:
• Protect the safety of the Herbert Hoover Dike;
• Reduce algal bloom risk lake;
• Reduce algal bloom risk in the estuaries;
• Maintain congressionally authorized navigation;
• Maintain congressionally authorized project purposes of recreation;

• Maintain flood control;
• Protect water supply;
• Enhance the ecology of the Lake Okeechobee;
• Enhance the ecology of the Caloosahatchee estuary;
• Enhance the ecology of the St. Lucie estuary; and,
• Enhance the ecology of South Florida.

Lacy said for navigation, the goal is to maximize the amount of time lake levels are about 12.56 feet.

Recreation is complicated, she added. “The plan that is going to optimize recreation will be more of a balanced plan.” Navigation is important for recreation. Enhancing ecology and reducing algal blooms are also important for recreation.

For example, some of the model options were:
• Plan 4A-1B — A plan that looks to enhance the ecology of Lake Okeechobee would also reduce the risk of algal blooms in the lake. This plan attempts to maintain stages within RECOVER ecological stages envelope by making releases when the lake is above the band and not when below.
• Plan 4A-B2 — This plan defines a seasonally varied target lake stage and then makes releases based on current stage, forecasts of lake inflow and target stages.
• Plan 1C-1 — This plan, which would minimize algal blooms in the estuaries, minimizes releases to the estuaries in June through August, when algal bloom risk is the highest. Lake releases primarily occur in September through December to bring lake levels down form the wet season.
• Plan 2C-1 — This plan reduces lake stages prior to onset of wet season to create adequate storage for the wet season. This plan aims to draw the lake down to a certain level every year.
• Plan 3 — This plan includes an expanded Beneficial Use band, which maximizes water stored in the lake at the onset of the dry season.
• Plan 4B-1 — This plan makes shorter term high flow releases from the lake to the Caloosahatchee Estuary to manage lake levels during March to May while providing a recovery period for the Caloosahatchee Estuary between pulses. Release and recovery periods were varied from 1-2 weeks and 2-3 weeks.

• Plan 4B-2 — This plan caps releases to the Caloosahatchee at 2,100 cubic feet per second (cfs) in the operational band with no cap to eastern or southern flows. This plan includes prioritizing southerly flows first as well as a ramp up/ramp down period.
• Plan 4C-1 — This plan does not make any lake releases to the St. Lucie estuary through the S-80. Basin runoff is allowed to backflow into the lake when the lake is below 14.5 feet.
• Plan 4C-2 — This plan makes shorter high flow releases from the lake to manage lake levels during March to May.

Lacy said they tried plans that prioritize the ecology of the Caloosahatchee estuary and plans that prioritize the ecology of the St. Lucie estuary. They also tried plans that switch back and forth between the two estuaries, alternating years for releases to reduce the number of years each estuary has flows over their salinity envelope thresholds from lake releases; alternating years provides longer recovery time for the estuaries.

All of the conceptual plans maintained the Water Shortage Management Band on the lower end of the schedule. “The line that we don’t make releases below that band doesn’t change,” she said.

Calvin Neidrauer, chief hydrologist for the South Florida Water Management District, said they will look holistically at all of the results. He said they will also consider the need to move more water south to Everglades National Park during the dry season.

“Pareto sorting has been around for decades,” he said. All of the runs are compared to each other to determine those runs that are Pareto-optimal.

Alev said the next step is to narrow down the 27,000 plans to nine possible plans.

“This is meant to be a learning process,” said Tim Gysan, project manager.

He said LOSOM should be ready into effect in 2022 when the Herbert Hoover Dike repairs are complete.

The PDT members were given access to the data from the model runs.

Each stakeholder group may select five to 10 plans for consideration for a sub-objective, which will be reviewed by the sub-objective groups.

In the next round, they will consider how the plans affect other objectives. For everyone to share the benefits of a new lake schedule, compromise is necessary, he explained.

“We know management for one specific objective doesn’t work,” he said.

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