Corps to maximize flows from lake

OKEECHOBEE — The U.S. Army Corps of Engineers will increase water releases to the east and west on Friday, but the lake, already at its highest level since December 2005, is expected to continue to rise.

The U.S. Army Corps of Engineers Jacksonville District will further increase flows from Lake Okeechobee this weekend in an effort to stem the rise in water level brought about by recent heavy precipitation.

The South Florida Water Management District has received about 500 percent above the normal rainfall since South Florida’s “dry” season started in November.lake releases photo

Starting Friday, Feb. 5, the Corps will remove specific target flows and release as much water as practical through the Moore Haven Lock (S-77) located on the west side of the lake, and the Port Mayaca Lock (S-308) located on the east side of the lake.

Flows will vary based on downstream conditions in the Caloosahatchee River/Estuary and the St. Lucie Canal/Estuary.

“Even with the discharges that started last week, the lake continues to rise,” said Colonel Jason Kirk, Jacksonville District commander. “With additional rain in the forecast, we believe we must further increase flows to reverse the upward trend of the lake.”

On Thursday, the lake stage was 16.25 feet. Depending on runoff and other factors, the Corps could achieve flows from the lake up to 9,300 cubic feet per second (cfs) in the Caloosahatchee basin and up to 7,600 cfs in the St. Lucie basin.

However, water managers will continue to give priority toward using those basins for accumulated runoff to reduce potential for flooding of nearby property owners.

The maximum amount that can be released from the lake is constrained by several factors including the water control structures, the amount of water already flowing into the St. Lucie and the Caloosahatchee from the surrounding basins, and the tides.

Even with these “maximum practical” releases, the lake is still expected to continue to rise, as water can flow into the lake three times faster than it can be released, explained Jim Jeffords, chief of the U.S. Army Corps of Engineers, Jacksonville District Operations Division.

With the lake level nearing 16.5 ft., public safety is their top priority, he said.

The Corps has been conducting dike inspections once a week, with inspectors walking along the dike to look for problem areas. Those problem areas are ranked from category 1, which indicates a wet area, to category 4, which indicates water eroding the dike.

Inspections of the south end of the Herbert Hoover Dike have revealed three areas with clear water seepage between Port Mayaca and Moore Haven. These category 3 clear water flows are not considered a danger to the dike. The danger comes with muddy flows, which would indicate the water is eroding the earthen dike.

When the lake level hits 16.5 ft, the Corps will inspect the dike twice weekly.

Should the lake level hit 17 ft., they will go to daily inspections.

While coastal communities are already complaining about the environmental effects of the water released from Lake Okeechobee, Mr. Jeffords said, to date, most of the water flowing into the ocean from the St. Lucie and the Caloosahatchee has been from those basins.

Only 28 percent of the water released to the east and the west since November came from Lake Okeechobee.

Despite concern about the rising lake level, the Corps and the district have allowed some water to be backpumped into the lake from the south.

Mr. Jeffords said there are three backpumping stations. One — called the S-4 — is used to prevent flooding in the City of Clewiston. The other two — labeled the S-2 and the S-3 — are used to reduce flooding in the Everglades Agricultural Area (EAA).

He said the backpumped water is a minimal amount when compared to the vast lake. It contributes “maybe an additional inch” to the lake, he said.

He said the S-4 is routinely used as needed, based on the level of the Clewiston Canal. The district decides whether to use the S-2 and the S-3. Last week, water managers allowed backpumping for four days — during which an estimated 10 billion gallons of water was pumped into the lake from the EAA.

Mr. Jeffords said they could not send that water south because all of the conservation areas in that direction are already flooded. There is no way to move any water south right now, he said.

As the lake rises, concerns increase about the possibility of a breach in the dike that would result in catastrophic flooding south of the lake where some land elevations are only 11 or 12 ft. above sea level.

There is always some risk, said Mr. Jeffords. The higher the lake rises, the greater the risk.

The Corps maintains the lake at levels detailed in the Lake Okeechobee Regulation Schedule (LORS), which was established in 2008 to balance the many demands on the lake for environmental, agriculture, urban and recreational uses.

The LORS optimum level is 12.5 feet to 15.5 feet. These levels allow the lake to have its natural highs and lows that are essential to the health of the big lake’s own ecosystem and fishery.

Elevation in Okeechobee County ranges from around 15 ft. above sea level near the lake to 75 ft. above sea level in the northern part of the county.

About the dike

Herbert Hoover Dike is a 143-mile earthen dam that surrounds Lake Okeechobee — the heart of the Kissimmee-Okeechobee-Everglades system.

The original dike was constructed with gravel, rock, limestone, sand and shell.

Since 2007, the Corps has made a significant investment — over $300 million — in projects designed to reduce the risk of catastrophic failure of the aging structure. Actions taken include installing a cutoff wall, removing and replacing water control structures (culverts) and conducting a variety of studies and technical reviews.

As the lake level rises, the chance of a breach of the earthen dike increases.

The risk is greatest at the south end of the big lake, where the land elevations are lower.

The lake level can rapidly increase if a tropical storm or hurricane hits. After

Tropical Storm Faye hit the state in 2008, the level of Lake Okeechobee rose more than 2 feet in 10 days.

At 16 feet, the chance of dike breach is about 5 percent, according to a 2008 study by the Corps.

At 18 feet, the probability of dike failure is 45 percent.

Should the lake level reach 20 feet, a dike breach is expected.

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