We are fortunate to work with many stakeholders in Florida who passionately care about the environment, our waterways, and the work we are doing as part of the Comprehensive Everglades Restoration Project (CERP).
We know there is much interest in improving the health of the St. Lucie Estuary from our stakeholders, and in light of that, I’d like to provide more detailed information about the Operational Testing and Monitoring Phase (OTMP) of the C-44 Reservoir and Stormwater Treatment Area (STA). The reservoir and STA are operational and providing benefits to the Estuary, even as we go through OTMP.
The C-44 Reservoir project, authorized by Congress in 2007, was designed to capture and clean local basin runoff along the C-44 basin and deliver it to the St. Lucie Estuary in better timing, quantity, and quality. The STA was completed in November 2019, and the reservoir was completed in November 2021.
The reservoir measures two miles by three miles and 15 feet at its deepest point, and the reservoir and adjacent 6,300-acre STA can store a combined 60,500 acre-feet of water. It’s the first fully completed reservoir construction project among the 68 components in the Comprehensive Everglades Restoration Plan (CERP), designed to restore, protect, and preserve America’s Everglades.
Since its completion, the C-44 Reservoir has been in OTMP, which allows us to ensure the project features perform as designed and evaluate the operations before finalizing the project operations manual and turning the project over to the sponsor. I want to emphatically state up front that we have full faith and confidence in the structural integrity of the C-44 Reservoir embankment.
In OTMP, we did observe some seepage in the adjacent canal that will become a maintenance issue if not addressed, so we are addressing it before we turn the reservoir over to South Florida Water Management District (SFWMD) for operation. Previously the term “leaking” had been used to explain this complex issue in simple terms, but it is not an accurate portrayal of the situation.
To start OTMP, we incrementally filled the reservoir to observe its performance. We paused the initial filling process at 10 feet in March 2022 after observing wet canal banks in discrete areas of the southern and western perimeter of the seepage canal. All earthen dams have seepage that we control and manage in a variety of ways. In this case, we were seeing seepage in an area we did not anticipate due to geological differences underground.
When you work on structures as large as these, the geology and conditions underground may be very different in one part of the construction area than another. We use the best engineering and design at the outset and use the OTMP period to check that everything is functioning as designed. If there is something we find that needs to be addressed, we have this process in place to do that.
The Corps is currently designing a seepage management feature in those areas of the perimeter canal, where seepage was observed. We have selected an alternative called a Relief Well to address the seepage, and it is currently under preliminary design. Additional data collection and soil boring testing are ongoing that will aid us in implementing the design concept at discrete areas at the west side and south side of the reservoir. The number, location of relief wells, and total estimated costs is still to be determined as the design phase continues. We have a video on our U.S. Army Corps of Engineers Jacksonville District Facebook page that explains this in depth.
The C-44 Reservoir has a 15-foot maximum fill depth. During the OTMP, we are operating the reservoir up to 10 feet until the seepage management features are complete. The water depth at any given time is largely dependent upon local rainfall in the C-44 basin area. We utilize every opportunity to pump water into the project. If there is excess water in the basin and there is room in the reservoir to take water (below 10-foot depth currently – below 15-foot depth in the future), water will be pumped in up to the set limit.
Since initial filling operations, pumping into the reservoir has continued according to the project operating manual but has not exceeded 9 feet. Thus far, there has not been any time where the 10-foot limit has limited the ability for water managers to utilize the project. Since OTMP started in January 2022, the project has reduced outflows of the C-44 canal into the St. Lucie Estuary by about 12,800 acre-feet, roughly like filling 12,000 football fields one-foot deep.
We regularly post information about our projects on our website. You can find additional information about the C-44 Reservoir at: https://www.saj.usace.army.mil/Missions/Environmental/Ecosystem-Restoration/Indian-River-Lagoon-South/