OKEECHOBEE — How much effect would the completed LOWRP have on Lake Okeechobee discharges? A lot depends on just how much rain falls, where the rain falls and when.
As many officials with the U.S. Army Corps of Engineers (USACE) are fond of reminding the public “most of the time, Mother Nature is in charge.”
Computer modeling has indicated that, combined with other Comprehensive Everglades Restoration Plans (CERP) projects already approved — and in some cases already under construction — LOWRP will cut harmful releases by about 80%. That means in a dry year (like 2019, there would be no releases, and in an “average” year, the storage capacity would be enough to prevent the need for discharges. In very wet years (like 2017), discharges to the coastal estuaries may be required to keep the lake within the safety zone for the integrity of the Herbert Hoover Dike, but the discharges would be reduced from what would have been required without LOWRP.
The LOWRP features would also make is easier for the corps to keep Lake Okeechobee within the healthy 12 feet to 15 feet range which has been deemed by the scientists on the RECOVER (Restoration, Coordination & Verification) Executive Committee to be best for the health of the lake’s ecology.
Storing water vs. sending excess water to tide
In the 2018-19 dry season, in an effort to lower the lake below 11 feet to allow the vegetation in the marshes to recover from the devastation of Hurricane Irma, the corps released water to the St. Lucie (which needs no lake water) and also released water to the Caloosahatchee at much higher levels than the minimum dry season beneficial flow lake releases required to prevent saltwater intrusion in the river.
That excess lake water “sent to tide” east and west during the dry season equaled about 1 foot of water on Lake Okeechobee.
If LOWRP had been in place, instead of sending that water to tide, the goal of lowering the lake to benefit the marshes could have been achieved by storing that water. As it turned out, the 2019 wet season was the shortest on record and the stored water could have ensured a backup water supply was available.
Reducing harmful discharges
During the 2016, 2017 and 2018 wet seasons, heavy rainfall draining into the lake, primarily from the watersheds north of Lake Okeechobee, sent the lake level into the danger zone for the Herbert Hoover Dike, and resulted in harmful releases of freshwater to the coastal estuaries.
In 2016, the wet season started with the lake at 14.38 feet. Due to heavy rainfall pushing the lake level beyond the safety zone for the dike integrity, 684,484 acre-feet of water was released to the Caloosahatchee River and 292,731 acre-feet was released to the St. Lucie River. If LOWRP had been in place, the ASR wells could have been used throughout the year to help keep the lake closer to the target zone. This would have allowed them to start the wet season with the lake about 1 foot lower, providing that additional storage capacity and reducing the amount of water that had to be released east and west. In addition, the increased storage in the C-44 reservoir on the St. Lucie Canal and the C-43 reservoir on the Caloosahatchee along with the EAA reservoir south of the lake, would further reduce the risk of discharges.
In 2017, the lake started the dry season at just 10.93 feet, but the wet season brought Hurricane Irma, which drove the lake level up. That wet season, 556,995 acre-feet were discharged with the Caloosahatchee and 319,122 to the St. Lucie. If LOWRP had been in place, the ASR wells and WAF could have reduced the need for some of those discharges. The WAF has a capacity of 46,000 acre-feet. While ASR storage is not a quick fix, every gallon of water that can be sent into the wells is a gallon that won’t have to go to the estuaries.
“In the limestones of the Floridan Aquifer, the rate of water storage is based on the pump on the wellhead,” explained USACE Senior Hydrogeologist June Mirecki. “The pumping rate for each CERP ASR well is 5 million gallons per day (MGD) = 8 cubic feet per second = 15.3 acre-feet per day. The total volume that can be stored depends on how many days each well can pump.” For example, the single ASR test well on the Kissimmee River pumped (recharged into the aquifer) continuously for six months in 2014 to store 1 billion gallons of water. “LOWRP recharge durations will vary, and can be longer depending on lake stage.” she added.
LOWRP Project Manager Tim Gysan added: “One of the big benefits of ASR wells is the ability to store water over several years leading to the potential for large reserves when dry conditions happen. This is how large scale ASR implementation can serve to improve environmental and water supply conditions much more than a onetime fill above ground reservoir.”
Slow the flow?
Before channels were dug to provide flood control for South Florida residents, businesses and farms the water in the basin north of Lake Okeechobee sheet flowed very slowly into the lake. According to the U.S. Geological Service, before the Kissimmee River was channelized, water that fell at the top of the system took about six months to travel all the way to Lake Okeechobee. Now that hydrological trip takes just weeks. Speeding up the flow means less water evaporates into the air or percolates into the earth, recharging the aquifer. It also means the lake fills up so quickly it destroys the submerged aquatic vegetation — the lake’s own filter system. If the water rises faster than the vegetation can grow, it can damage or kill the vegetation. According to the SFWMD Water Conditions Report provided by SFWMD Assistant Executive Director John Mitnik, the recommended rate for the lake to rise is about 0.5 feet per two weeks (about 3 inches a week). In 2017, after Hurricane Irma, the lake rose 3.5 feet in less than a month.
Some numbers to consider:
• 1 inch on Lake Okeechobee equals about 12 billion gallons of water.
• 80 ASRs in the project would provide annual storage volume of 448,000 acre-feet, which equals 145.9 billion gallons of water — about 1 foot of water on Lake O.
• 3.068 acre-feet equals about 1 million gallons of water.
• The WAF would provide 46,000 acre-feet of storage — about 1 inch on the lake.
• Wetlands are not storage features, although restored wetlands do hold some water.