As the runoff from rainfall during Hurricane Irma flows south through the Kissimmee River basin, Lake Okeechobee could top 17 ft. according to the U.S. Army Corps of Engineers.
On Sept. 7, the lake level was 13.7 ft. On Sept. 14, the lake level was 14.83 ft. By Sunday, Sept. 17, the lake had risen to 15.5 ft. By Tuesday, Sept. 19, it was 15.66 ft.
Under normal conditions, water can enter the lake six times faster than it can be released (even when all outflow structures are at maximum capacity), which makes it very difficult for the Corps to slow the lake’s rise. Since many of the lake’s outlets currently have no capacity for outflow, water has been entering about 10 times faster than it could be released.
The water managers estimate rain from Hurricane Irma could drive the lake up to 17 ft., the highest level in 10 years. The Corps tries to keep the lake level between 12.5 ft and 15.5 ft., which is considered optimal both for the lake’s ecology and to reduce the risk of dike failure.
Starting Friday, Sept. 15, the Corps began to release as much water as possible east at Port Mayaca, between 2,000 and 4,000 cubic foot per second (cfs) to the C-44 canal. On Sept. 15, the average was 2,824 cfs. Water could not be released to Caloosahatchee at Moore Haven at that time because the river was already in flood stage from basin runoff and high tides.
On Tuesday, Sept. 19, the Corps began releases to the Caloosahatchee River at Moore Haven, ranging from 2,000 to 4,000 cfs.
Water is entering the lake about 40,000 cfs, mostly from the north.
Some water has been backpumped from south of the lake to prevent flooding in the cities south of the dike.
For the 24 hour period ending Sept. 18, about 4,000 cfs was entering the lake from the south through the pumps controlled by South Florida Water Management District. Corps officials expect that flow to stop within a week.
“We still have high water levels in the canals around the populated areas of Belle Glade and South Bay,” explained Randy Smith of SFWMD. “When the pumps are not running, the water levels are climbing back up due to the saturation in the EAA. We do see that changing as the last few days have been very hot and dry. If this continues the district hopes to bring water levels down to levels that do not pose a safety threat to families and businesses in the area and cease pumping operations as soon as possible.”
Laureen Borochaner, chief of the Engineering Division, U.S. Army Corps of Engineers, said the Herbert Hoover Dike – the 143 mile earthen berm around the big lake – is in good shape.
Prior to the storm hitting the dike area, the Corps pre-positioned inspection teams so they could start inspections as soon as the hurricane winds subsided. The dike inspection was completed on Sept. 12.
Other than minor erosion, the inspectors saw no signs of distress in any of the areas inspected.
“We will continue to monitor Herbert Hoover Dike as lake levels rise,” she said.
Before the storm hit, there was concern that three areas of the dike with cofferdams were at risk of overwash or spillage during the hurricane. The cofferdams are in place in areas where culvert replacement work is underway. In those three locations – one near Clewiston, one between Belle Glade and Pahokee, and one near Lakeport – part of the dike has been excavated in order to replace culverts. Metal cofferdams are in place to hold back the lake’s water, but the cofferdams are not as tall as the dike. The lowest cofferdam is about 25.3 ft., about 10 feet shorter than the dike wall.
“There was no evidence of overwash or overtopping at the cofferdams during Hurricane Irma,” she said.
She noted flooding in Glades County was from direct rainfall in that area.
“We’re trying to get ahead of the curve,” said Ms. Borochaner.
“As water continues to come into the lake from the Kissimmee basin, the lake will continue to rise. We want to minimize the rise of Lake Okeechobee as much as possible.
Based on our modeling and calculations, the Corps expects the lake to continue to rise for about two weeks.
Mr. Borochaner said the highest recorded level for the lake was 18.77.
“Beyond 18.77 is at a level it has not been tested,” she said.
According to the Corps, lake water cannot be released to the south because that area is already flooded, and flow to Florida Bay cannot be increased. Flow from the water conservation areas south of the lake must go under the Tamiami Trail to reach Florida Bay, and currently there is only one mile of raised roadway completed.