Water backflowing into lake at Port Mayaca

PORT MAYACA — The U.S. Army Corps of Engineers allowed some nutrient-rich water from the St. Lucie Canal to backflow into Lake Okeechobee this week in anticipation of heavy rainfall expected this weekend.

The move will help protect the St. Lucie Estuary from excessive flow which could lower the salinity levels and make the estuary more vulnerable to ecological damages.

Erica Skolte, with the corps, explained that this is not a change to the lake schedule because the St. Lucie lock remained closed. Nothing in the schedule prevents backflow into the lake from the St. Lucie Canal.

On Tuesday, July 30, flow at the Port Mayaca lock averaged 592 cubic feet per second into Lake Okeechobee (about 382 million gallons per day). On Wednesday, the gates at Port Mayaca were opened.

While a millions gallons sounds like a lot of water, it is a “drop in a bucket” for the Big Lake. One inch on Lake Okeechobee equals about 12 billion gallons of water. At a flow rate of 592 cfs., it would take more than month to raise the lake level by one inch.

Over the past seven days, the average backflow into the Lake at Port Mayaca was 85 cfs. The seven-day average flow east from the St. Lucie Canal into the St. Lucie River was 356 cfs. All of the flow through the St. Lucie lock to the east was local basin runoff.

No water from Lake Okeechobee has flowed into the St. Lucie Canal since March 30. The flow at Port Mayaca is gravity driven. When the lake level is lower than the level in the canal, the water backflows. On Thursday, the lake level was 11.65 feet.

The corps tries to keep the St. Lucie Canal level between 14 and 14.5 feet. When the lake level is lower than the water level in the canal, water backflows into the lake.

The extra nutrients from the St. Lucie canal water could feed the algae in Lake Okeechobee. Historically, the phosphorus level in the St. Lucie Canal is higher than the phosphorus level in the lake. Local basin runoff from farms and subdivisions flows into the St. Lucie Canal unfiltered. Any nutrient flow into the lake provides food for the algae.

With heavy rain expected this weekend, the South Florida Water Management District (SFWMD) is preparing the regional flood control system to handle heavy local rainfall expected.

“We are always working year round to keep our regional flood control system prepared as we continue to watch developing conditions so we can spring into action when needed to protect communities and the environment,” said SFWMD Interim Assistant Executive Director and Chief Engineer John Mitnik. “Not just with this approaching tropical wave, but also with the heart of hurricane season approaching, now is a good time for residents to do their part by ensuring their storm drains and swales are clear of debris and also to familiarize themselves with what agency provides local drainage for their property.”

The storm system is forecasted to drop as much as 4-6 inches of rain across some areas of the district by Sunday as the storm passes by South Florida.

On Wednesday, SFWMD began drawing down canals throughout its regional flood control system to ensure capacity to take stormwater from local drainage districts and municipalities to prevent flooding. The district also held a call with local drainage districts and municipalities to coordinate flood control efforts as the tropical wave approaches.

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