Lake level ‘deviation’ is calculated risk State and federal agencies meet Tuesday

The “deviation” plan for Lake Okeechobee proposed by the U.S. Army Corps of Engineers would allow the corps to release less water east to the St. Lucie Canal and west to the Caloosahatchee River when harmful algal blooms (HABs) are present and more water when there are no HABs present. That means fewer releases in the hotter summer months when algal blooms are more common and more releases during the winter months when HABs are less likely.

Special to the Lake Okeechobee News/USACOE
The U.S. Army Corps of Engineers manages the flow of water in Lake Okeechobee and connecting canals to balance a variety of competing needs including water supply, the environment and wildlife habitat.

Such a plan requires the water managers to predict how much rain will fall during the wet season. Releasing too much fresh water to tide during the dry season could mean water shortages later if they guess wrong.

At the May 7 multi-county meeting in Okeechobee, Lt. Col. Jennifer Reynolds of the U.S. Army Corps of Engineers admitted the corps took a calculated risk in letting more water flow east and west to tide during the past dry season.

“We never tried to bring the lake to 10.5 feet, but we did want to see the lake below 12 because what our scientists were telling us was that below 12 feet is what would allow the grasses to be able to germinate, that enough sunlight would get to enough lake bottom to allow those grasses to germinate and grow during the beginning of this dry season,” she explained.

She said the corps sent pulse releases of freshwater to both estuaries prior to the oyster season, while monitoring all three ecosystems, to do what they could to rebuild some resiliency in the three ecosystems.

“What we were hearing from all of the experts about weather forecast was there was not a risk of drought this year because of the weather patterns they were seeing,” she said.

“Could we have gotten it wrong? Yes.

“Could we still have it wrong? Yes. Because we can’t predict exactly what Mother Nature is going to do and we all know when we try to count on it, we get it wrong every time,” Lt. Col. Reynolds said.

“The most significant impact on the lake this time of year is rainfall and evaporation, and so what we are doing in terms of releases from the lake does not make a significant difference on the lake this time of year. What makes the most significant difference is what Mother Nature does,” she said.

One thing Mother Nature will do every year, no matter how much or how little rain falls, is to send water into the atmosphere through evaporation.

While much of the water that flows into the lake is controlled by the locks, culverts and other water control structures, most of the water that leaves the lake does so by evapotranspiration into the air and percolation through the earth into the aquifer. Evapotranspiration is the sum of evaporation and plant transpiration from the Earth’s land and ocean surface to the atmosphere.

Evapotranspiration rates are difficult to measure. Scientists use different models. On average, they estimate Lake Okeechobee drops by between 4.3 feet and more than 5 feet each year due to the movement of water into the air.

Over the past dry season, the corps released more water west to the Caloosahatchee River than the current schedule dictates. South Florida Water Management District has guaranteed the river a minimum flow of 450 cfs during the dry season. For most of the past dry season, the flow was 800 to 1,000 cubic feet per second, measured at the Franklin Lock. The 1,000 cfs level is considered the optimal flow to prevent salt water intrusion in the river and maintain desired salinity levels in the estuaries. For six weeks in February and March, additional lake water was sent to tide in an attempt to lower Lake Okeechobee before the start of the wet season. These releases occurred when the lake level was below 13 feet above sea level, and LORS 2008 did not call for releasing any freshwater to tide, (apart from the 450 cfs guaranteed to the Caloosahatchee River.) For six weeks in February and March, the corps increased the Caloosahatchee flow to 1,800 cfs. For 21 days in February and March, the corps released 500 cfs east at Port Mayaca to the St. Lucie Canal. For another three weeks in March, flow to the St. Lucie was 250 cfs. LORS 2008 did not call for any releases to tide during that period.

The Lake Okeechobee System Operating Manual will be the topic of discussion at a Project Delivery Team (PDT) meeting on Tuesday, Aug. 20 from 9:30 a.m. to 4:30 p.m. in John Boy Auditorium, 1200 W.C. Owens Ave., in Clewiston. Members of the public are welcome to attend the government agency PDT meeting and provide comment during designated public comment periods.

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