Current dry conditions are good for Lake O

Posted 4/9/21

WEST PALM BEACH – “It has gotten pretty dry, which in some respects is a welcome break,” John Mitnik explained during his Water Conditions Report

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Current dry conditions are good for Lake O


WEST PALM BEACH – “It has gotten pretty dry, which in some respects is a welcome break,” John Mitnik explained during his Water Conditions Report at the April 8 meeting of the South Florida Water Management District Meeting (SFWMD).

March brought roughly about 37% of average rainfall, he explained. Since the start of the dry season the district has averaged about 60% of average rainfall.

“Over the month of March, with that drier weather, the lake has started the recession we typically see during the dry season,” he explained.

The lake was just over 14 feet above sea level on April 8. There’s roughly 50% chance lake will be 12.5 to 13.5 feet on June 1, Mitnik said.

Ideally, the lake should slowly fall to around 12 feet or 12.5 feet by the start of the wet season in June and rise to about 15.5 feet by the start of the dry season in November. Seasonal highs and lows, with water flowing slowly into the lake during the wet season and the lake level slowly falling during the dry season would mimic the natural system.

South Florida is expected to continue to have La Niña-like dry conditions for the rest of the dry season, Mitnik said. The lake is expected to continue to recede for the rest of the dry season.

The majority of the water leaving Lake O – other than evaporation – is moving south, said Mitnik.

For the past seven days, 1,334 cubic feet per second flowed west to the Caloosahatchee, as measured at the Franklin Lock. That is within the beneficial flow range for the river. Flows below 450 cfs (measured at the Franklin Lock) are considered harmful as the salinity levels in the estuaries are too high. Flows higher than 2,800 cfs are also considered harmful because the salinity levels drop too low. The ideal beneficial freshwater flow at the Franklin Lock advocated by estuary scientists is around 1,000 cfs, but the ideal salinity level varies for different parts of the estuaries. Some flow at the Franklin lock is from local basin runoff. For the past seven days, the flow at the Moore Haven lock, where lake water enters the Caloosahatchee, was 1,160 cfs. (Starting April 10, the U.S. Army Corps of Engineers will reduce the flow at the Franklin Lock to 1,000 cfs.)

For the past seven days, flow from the lake at the Port Mayaca Lock averaged 215 cfs. Flow at the St. Lucie Lock, which is a mixture of lake releases and local basin runoff averaged 339 cfs. (Starting April 10, the corps will stop flow from the lake to the St. Lucie canal at Port Mayaca so any flow at the St. Lucie Lock will be from local basin runoff.)

Freshwater flow of around 2,300 cfs is moving south from the lake, Mitnik said. That water is used for agricultural irrigation and urban water supply with some water going to the stormwater treatment areas (STA) which clean water and move it south to Everglades National Park. He said it takes about 10-14 days for water to move through the STAs. The STAs also need water, he explained. In the drier times, they may put 500 cfs in the top of the STAs and get 400 cfs out because some of the water is used by the vegetation in the STAs and to keep the water levels optimal in the STAs, he explained.

According to the corps, about 1,100 cfs is moving south under the Tamiami Trail to Everglades National Park.

So far this water year (since May 1, 2020):
• About 2.6 million acre feet of water has flowed into Lake Okeechobee from the north.
• The Caloosahatchee River flow has been about 1.75 million acre feet of water. About 700,000 acre feet of the flow to the Caloosahatchee came from Lake O.

• Roughly 360,000 acre feet flowed into the St. Lucie from the C-44 canal. About 200,000 acre feet of that flow came from the lake. (Note: In that same Water Year, about 100,000 acre feet from the C-44 basin backflowed into Lake Okeechobee at Port Mayaca, so the equivalent of half of the flow “from the lake” initially originated in the C-44 basin. Flow at Port Mayaca is gravity flow. When the lake is below 14 feet, water can backflow into the lake from the C-44 basin.)
• 1.9 million acre feet flowed to Everglades National Park.
• 3.7 million acre feet that fell on urban areas on the east coast (east of the East Coast Protection Levee) moved to tide.

“We’re heading in the right direction,” said SFWMD Governing Board Member Ron Bergeron, noting the benefits of removing impediments to the flow south, such as the partial bridging of the Tamiami Trail and removal of the old roadbed.

SFWMD Governing Board Member Jacqui Thurlow-Lippisch noted that before the East Coast Protection Levee was built, some of that 3.7 million acre feet of water that now goes to tide would have gone to Florida Bay

Mitnik said abnormally dry areas have increased across the district. “We’ll see what the rains this weekend bring,” he added.