What will Hurricane Ian mean for Lake Okeechobee?
On Sept. 27, Hurricane Ian was predicted to make landfall on the Gulf Coast and continue northeast through the center of the state, dumping heavy rainfall along the way.
The good news is that at around 13 feet, Lake O has plenty of capacity to store water without risking the integrity of the Herbert Hoover Dike, the earthen berm which surrounds the second largest freshwater lake within the confines of the continental United States.
The bad news is that if the water comes in too fast, it will bring with it more nutrient load – phosphorus and nitrogen that can feed algae and encourage algal blooms. After Hurricane Irma in 2017, the phosphorus load in water entering the lake doubled.
If the water level rises faster than the submerged aquatic vegetation (SAV) can grow, the rapid rise in the lake can also damage or kill the SAV. SAV helps clean the water and provides critical habitat for fish.
On Sept. 27, Lake Okeechobee was at 13.18 feet above sea level.
Very little lake water has been released to the Caloosahatchee River since the start of the wet season. The target flow for the Caloosahatchee River is measured at the Franklin Lock. If the local basin runoff meets or exceeds the freshwater flow needed for the estuary, no lake water is released. The target for much of the wet season was 457 cubic feet per second (cfs). On Sept. 9, with the lake in the Water Shortage Management Band, the U.S. Army Corps of Engineers started measuring target flow at the Julian Keen Jr. Lock at Moore Haven, and set the target flow at 0 cfs. That means even if the flow at the Franklin Lock was below 457 cfs no water was released from Lake O.
On Sept. 27, flow at the Franklin Lock was 5,733 cfs, all from local basin runoff.
No lake water has been released to the St. Lucie River since April 2021. Water from the St. Lucie basin backflows into the lake if the lake level is below 14 feet. On Sept. 27, flow into the lake from the St. Lucie Canal (C-44 canal) at Port Mayaca was 995 cfs.
On the average, about half of the water that flows into Lake Okeechobee comes from the Kissimmee River. For the past wet season, due to lack of rainfall, there was very little flow to the lake from the Kissimmee. For months, there was no flow at all at the S-65 structure, where the Lake Kissimmee meets the river. On Sept. 27, flow at the S-65 structure was 6,6018 cfs, and thanks to additional basin runoff, flow at the S-65A structure south of the S-65 structure was 7,068 cfs.
Flow at the S-65E structure, which sends water from the river into Lake O was 4,953 cfs.
Why the difference between the S-65A structure and S-65E? The center third of the Kissimmee River has been restored by filling in the manmade channel and forcing water back into some of the original river bends. This causes the water to spread out over a vast floodplain and slows the flow. Slowing the flow means there is more time for the vegetation to clean the water. It also provides more time for water to percolate into the earth, recharging the aquifer.
When it comes to Lake Okeechobee, as U.S. Army Corps of Engineers officials are fond of reminding the public “one big storm can change everything.” The impact of Hurricane Ian remains to be seen.
There’s something else corps officials often remind us: “Most of the time, Mother Nature is in charge.”