JACKSONVILLE — The U.S. Army Corps of Engineers, Jacksonville District (USACE) began making low-flow releases from the C-44 reservoir Monday to create storage for potential large rainfall events due to the reservoir approaching its current maximum operational depth of 10 feet.

USACE and South Florida Water Management District (SFWMD) increased releases at S-402 to target 300 cubic feet per second. This structure releases water into the C-44 Stormwater Treatment Area (STA) which then passes over an uncontrolled weir (S-404) back into the C-44 canal. The C-44 canal releases into the St. Lucie Estuary via St. Lucie Lock and Dam (S-80), where those releases are combined with basin runoff from the C-44 watershed. No Lake Okeechobee releases are being made at the Port Mayaca Lock and Dam (S-308).

The intent of releasing at S-402 is to reduce reservoir levels to approximately seven feet so it can accept water from  potential large rainfall events and protect the St. Lucie Estuary from any associated high flows from those events. This strategy helps achieve the C-44 project benefits of improving the timing, quality, and volume of flows into the St. Lucie Estuary.  Water being released from the C-44 STA at S-404 has been treated through the STA and will have less nutrients than direct C-44 basin runoff.   

Our water managers are watching the total inflows into the estuary from C-23, C-24, Ten Mile Creek, and the tidal basin to evaluate when and how much to release to target optimal total inflows. As they evaluate current conditions, they are making adjustments daily so as not to exceed 1,400 cfs of total inflows into the estuary, which is the high end of the RECOVER optimal estuarine salinity performance metric of 150-1,400 cfs. Flows within this range will not cause adverse affects to the ecology of the St. Lucie Estuary.

While we can’t specify a timeframe for how long the releases will continue, the goal is to reduce the reservoir to approximately seven feet in depth while maintaining S-80 releases into the estuary below 1400 cfs. The weather will impact runoff at all the inflow points into the estuary, and we will adjust the flow from S-402 as necessary.

The C-44 Reservoir has been in Operational Testing and Monitoring Phase (OTMP) since November 2021, and during this time, will operate at a maximum fill of 10 feet. The OTMP allows us to ensure that the project features perform as designed and evaluate the operations in the project operating manual. We will continue operational testing and monitoring of the C-44 reservoir throughout the wet season. 

Releases out of the reservoir are a necessary operational action and without this action the project cannot provide the benefits to the St. Lucie Estuary and its stakeholders. Releasing the water now at a lower rate, with less nutrients, and when total inflows are within the optimal range will allow us to maximize the opportunity to provide benefits. Doing this now will allow us to pump water into the project when flows are high in volume, high in nutrients, and when all the other basins are flowing at high rates into the estuary and is exactly what the project was designed to do. With this project online we will start to realize the benefits that the Indian River Lagoon South Project as a whole will achieve.