To lower the lake, where would water go?

Posted 2/27/19

Gov. Ron DeSantis and U.S. Rep. Brian Mast have proposed a new schedule for the operation of Lake Okeechobee that would lower the lake to 10.5 feet by the end of May, in order to leave enough …

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To lower the lake, where would water go?

Gov. Ron DeSantis and U.S. Rep. Brian Mast have proposed a new schedule for the operation of Lake Okeechobee that would lower the lake to 10.5 feet by the end of May, in order to leave enough capacity in the lake at the start of the wet season to prevent the need for any lake releases to the coastal estuaries.

Would it be possible to lower the lake that much? Let’s do the math.

Lee County officials have sued the South Florida Water Management District over dry-season flow. The Caloosahatchee River is currently guaranteed 400 cubic feet per second (cfs). Lee County officials want 700-800 cfs. They have stated that an average of 1,000 cfs during the dry season would be ideal.

One cubic foot per second is equal to 646,316 gallons per day, so 1,000 cfs equals 646,316,883 gallons per day.

One inch on Lake Okeechobee is about 12 billion gallons of water.

Before any changes, the Caloosahatchee River was already guaranteed 400 cfs, dry season flow, measured at the Franklin Lock, so the extra flow, if brought up to 1,000, is 600 cfs.

That extra 600 cfs per day is 387,790,133 gallons. Multiplying that by 180 days of the rainy season, that works out to 5.8 inches on Lake Okeechobee.

However, the annual total would probably be less than that because when there is rain in the Caloosahatchee River valley, flow from the lake is lessened or halted, as the runoff directly into the basin takes up some or all of that 1,000 cfs target at the Franklin Lock.

If the Caloosahatchee estuaries were to receive that “sweet spot” target level of dry-season freshwater flow, what would the lake look like? Exactly what it looks like today. During the current dry season, the corps has maintained that ideal target of an average of 1,000 cfs of flow at the Franklin Lock.

Releases higher than the 1,000 cfs average could harm the Caloosahatchee estuaries, according to Lee County officials. Martin County officials want zero releases to the St. Lucie Canal.

Even with the 1,000-cfs releases to the Caloosahatchee, the lake level, at 12.8 feet on Feb. 20, has been slightly rising due to dry season rainfall.

If Rep. Mast and Gov. Desantis want to lower the lake by 2 feet before the start of the rainy season, where will the rest of the water go?

“Send it south!” shout the residents of the east coast, urged on by organizations such as the “Bullsugar” group. Rep. Mast echoes this slogan on his website.

Canals do flow south from Lake Okeechobee, and according to an Audubon study, the equivalent of about 2 feet of water on Lake Okeechobee flows south annually from the Big O every year. Some water that flows south is used to irrigate the Everglades Agricultural Area (EAA). Water flowing south also goes to the stormwater treatment areas (STAs) and then to water conservation areas (WCAs) south of the EAA. Rainfall south of the EAA also helps full up the STAs and WCAs. Once the STAs and WCAs are at capacity, no water can flow south from the lake until water can be moved south from the WCAs. And two things block additional flow south: Tamiami Trail, and federal restrictions on flow.

The Tamiami Trail transecting the southern Everglades. When it was first constructed, it was closed during the rainy season when the road was under water. Years later, as the road was improved to accommodate heavier traffic and heavier vehicles, the improved roadway became a berm that blocked flow, and water levels north of the flow were maintained lower to prevent damage to the roadway. The U.S. Army Corps of Engineers has estimated about 11 miles of raised bridging is needed to restore flow south, but only 3.6 miles of bridging has been funded. Thanks to the bridging already completed, in the past year, the South Florida Water Management District was able increase the flow under the trail, but it did not make a significant difference in the lake level. Six months of the year (January to July), flow south is also blocked by the U.S. Department of the Interior to protect the nesting grounds of the endangered (Cape Sable sea sparrow.

One inch on the big lake equals 12 billion gallons of water So, if the corps was to lower the lake to 10.5 feet by May 31, where would that extra 288 billion gallons of water from Lake Okeechobee go? Gov. Desantis and Rep. Mast have yet to answer that question.