By SCCF Environmental Policy Director Matt DePaolis
As SCCF continues to evaluate the Lake Okeechobee System Operating Manual (LOSOM) Draft Environmental Impact Statement from the U.S. Army Corps of Engineers, we have found a clear benefit for the Caloosahatchee Estuary. Admittedly, the preferred alternative under LOSOM is not perfect. However, we believe that it is the most equitable solution for the needs of all stakeholders reliant on water within the system. If the preferred alternative is adopted, the Caloosahatchee will see an increase in beneficial flows, a substantial decrease in stressful and damaging flows, and an increase in extreme flows. With such a dense document, our staff wants to clarify some of the modeling contained within the plan and help interested parties digest the data.
A side-by side comparison of the Caloosahatchee as viewed from above Lighthouse Beach Park, with the left image showing the darker, murkier water in response to damaging water flows and the right image showing bluer, clearer water in response to optimal water flows. Images taken by the Sanibel-Captiva Conservation Foundation via drone. Take a virtual tour of the Caloosahatchee.
Under the preferred alternative, the Northern estuaries will receive a lower total volume of water. The Caloosahatchee Estuary (CRE) will see a 4% decrease of total release volume, and the St. Lucie Estuary (SLE) will experience a 40% decrease. While at first glance this may seem like a discrepancy, it reflects the different needs of the two estuaries. The goal of the SLE stakeholders is to aim for no water releases, while the CRE requires minimum flows to protect the health of the estuary. If the Caloosahatchee were to see a 40% drop in volume released, it would have a negative impact on our estuary, as the salinity would increase to stressful levels for oysters, tapegrass, seagrass, and other estuarine species.
The nuance of the preferred alternative lies in how and when water releases are distributed. In the CRE, just as too little water can cause damage, too much water will also compound stress on the environment. The LOSOM plan aims to have as many release events in the ‘optimal flow’ range of 750- 2100 cubic feet per second (cfs) as possible. It achieves this by reducing the amount of time the CRE experiences ‘stressful’ and ‘damaging’ ranges of 2100-2600 cfs and 2600-6500 cfs, respectively. Overall, the CRE will see a 23% increase in optimal events compared to the current release schedule, and the SLE will see an increase of 5%. Stressful and damaging flows for the CRE will decrease by 64% and 57%, respectively, and by 79% and 72% for the SLE. By structuring the releases in such a way, the estuaries will see a large increase in optimal flows. However, there remains a certain amount of water that will need to be released to the northern estuaries.
In order to limit the amount of stressful and damaging flows, and maximize the amount of optimal flows, a trade-off is required. To be able to release the necessary amount of water from the system, there must be an increase in ‘extreme’ flows of over 6500 cfs for the CRE and 3500 cfs for the SLE. The proposed plan will increase these extreme flow events by 21% (from 57 to 72 over the 53-year period assessed) for the CRE and by 1% (from 162 to 164) for the SLE. Through their modeling efforts, our scientists believe that this distribution is the most effective way to protect the health of our estuaries within LOSOM. We believe that it is better for the water quality of the estuary, the environment, and our way of life in coastal Florida to maintain optimal flows and the best water quality for as long as possible. The current plan will send extreme flows of water to the estuaries all at once. This will allow the lake to return to a safe level quicker, lessen the time that the estuaries are experiencing flows that are above optimal, and allow the estuaries to return to safe levels of releases. The other option evaluated was to lower extreme flows and increase the amounts of stressful and damaging flows throughout the wet season. Overall, we found that the consistent, lower water quality would be more damaging to the system than shorter, more stressful bursts. Restricting flows above optimal to only the most extreme will be like ripping a band-aid off to return the lake to a safe level, rather than slowly and painfully peeling off the adhesive.
While we at SCCF believe that the proposed management plan presents the best option under the current restraints, it is by no means perfect. There will be days where we see dark water, and our environment will suffer. We are hopeful that the operational flexibility within the plan will allow the Army Corps to synthesize new research into creative mitigation strategies for downstream environments. For instance, a recent study suggests that “pulsing” extreme flows so the salinity of the estuary is not at 0 for more than ~six days could greatly reduce oyster mortality. While this would increase the number of extreme events and potentially increase the days the Caloosahatchee is experiencing flows >6500 cfs, if it protects the ecosystems, it’s worth exploring. As our understanding of these systems is refined, we expect the Army Corps to incorporate new science into their management of the Lake in a way that will benefit all stakeholders. After years of work, SCCF believes that the current iteration of LOSOM is equitable to all stakeholders, a step up for the environment over the current schedule, and the best plan we are going to get.