By Jay Landers

Construction concluded in the fall on the final component of a long-awaited $419 million project aimed at improving water quality in Florida. Known as the Indian River Lagoon-South C-44 Reservoir and Stormwater Treatment Area, the project was completed in November. This vast new reservoir will assist efforts to capture and treat massive volumes of stormwater runoff that currently degrade three of the state’s more ecologically important water bodies.

New storage

The project provides more than 60,000 acre-ft of additional water storage and is designed to capture and cleanse nearly two-thirds of all stormwater runoff from a contributing drainage area of about 245 sq mi. Ultimately, the project will improve water quality significantly in the St. Lucie River, its estuary, and the Indian River Lagoon.

The Indian River Lagoon is “known as the most bio-diverse habitat in North America and has been designated an Estuary of National Significance" by the U.S. Environmental Protection Agency, according to a Dec. 6 news release from the South Florida Water Management District. (The SFWMD delivered the overall project with the U.S. Army Corps of Engineers as part of a 50-50 partnership.)

All three of the water bodies have long experienced harm as a result of discharges to the St. Lucie River from the C-44 Canal, which is also known as the St. Lucie Canal.

Constructed more than 100 years ago, the C-44 Canal helps prevent flooding along Lake Okeechobee, Florida’s largest freshwater lake, by conveying flows eastward from the lake to the St. Lucie River. However, large pulses of freshwater from the lake can alter the natural salinity conditions within the St. Lucie Estuary and the southern portion of the Indian River Lagoon, contributing to the decline of these important ecological areas.

Meanwhile, the C-44 Canal also collects and conveys stormwater runoff containing high levels of nutrients and other pollutants that further impair water quality within the St. Lucie River, its estuary, and the lagoon.

Authorized by Congress in the Water Resources Development Act of 2007, the C-44 Reservoir and STA is part of the larger Indian River Lagoon-South Restoration Project, which is itself a component of the overall Comprehensive Everglades Restoration Plan.

Besides the C-44 Reservoir and its STA, the Indian River Lagoon-South Restoration Project includes the construction and operation of three additional reservoirs and two new STAs that also will collect and treat runoff before it enters the St. Lucie River. Upon its completion in 2031, the overall restoration project will provide approximately 130,000 acre-ft of new water storage in the reservoirs and STAs and another 30,000 acre-ft of storage in natural areas.

In another step to benefit the St. Lucie River, the four reservoirs and three STAs that constitute the Indian River Lagoon-South Restoration Project will discharge to different points along the river rather than simply directing all flows to the river’s southern end, as happens today, says Michael Drog, the project manager for the C-44 project at the Corps’ Jacksonville District. This approach “creates a more gradual salinity gradient throughout the entire river,” Drog says.

A ‘significant complex’

The entire C-44 Reservoir and STA project occupies about 12,000 acres on the north side of the St. Lucie Canal in Martin County. A 100 ft wide intake canal extends nearly 21,000 ft from the C-44 Canal to a pump station that transfers flows from the intake canal to the reservoir. The pump station is equipped with four electric 1,750 hp pumps, each of which is designed to deliver 275 cfs, for a total capacity of 1,100 cfs, says Howard “Buff” Searcy Jr., a principal project manager for the SFWMD.

Enclosed within approximately 50,000 linear ft of earthen embankment having a nominal height of about 30 ft, the rectangular-shaped reservoir encompasses an area of roughly 2 by 3 mi, Drog says. The reservoir’s normal full storage elevation will be 15 ft. A perimeter canal around the reservoir collects seepage and returns it to the intake canal. All told, the 3,400-acre reservoir is a “pretty significant complex,” Drog says.

An 1,100 cfs pump station transfers flows from the intake canal to the C-44 Reservoir. (Image courtesy of the South Florida Water Management District)

Capable of holding up to 50,600 acre-ft, the reservoir provides storage of the water prior to flowing into independent STA cells that are enclosed within 7 ft high embankments. The water storage is “so that water withdrawals from the C-44 Canal can be maximized during wet weather flow events,” says Katie Duty, P.E., ENV SP, a project manager and principal for HDR, which designed all components of the overall C-44 Reservoir and STA project and provided on-site engineering during construction. “Water is released from the reservoir to the STA and back into the C-44 Canal when the St. Lucie Estuary requires water.”

Significantly cleaner water

A discharge structure in the northeast corner of the reservoir allows water to enter a distribution canal, which in turn conveys flows to each of the six individual cells ranging in size from 450 to 1,300 acres that constitute the 6,300-acre STA.

Controlled by fixed-weir outlet structures, the cells are designed to maintain depths of 1.5 ft, Searcy says. “Scientists have determined that 1.5 feet is an efficient depth for aquatic vegetation growth and water movement,” he says. “The time for water to move through the cell will vary with the conditions, such as rainfall, but is expected to be about 30 days.”

After leaving the C-44 Reservoir, flows enter the distribution canal, which conveys water to each of the six individual cells that constitute the 6,300-acre stormwater treatment area. (Image courtesy of the South Florida Water Management District)

A collection canal accepts effluent from each of the STA’s cells and returns it to the C-44 Canal by means of a spillway and box culvert. Upon leaving the cells, the treated water will be significantly cleaner than when it entered the STA, thanks to sedimentation and uptake of nutrients by aquatic vegetation, Searcy says. “There will be continuous testing and evaluation to determine the actual results, but there is expected to be approximately a 65% reduction in phosphorus and nitrogen,” he says.

The reservoir can store up to 50,600 acre-ft, while the STA can hold up to 9,900 acre-ft. Capable of treating 46 billion gal./year, the STA is expected to remove approximately 35 metric tons of phosphorus annually. In this way, the project is expected to improve water quality significantly in the St. Lucie River, its estuary, and the Indian River Lagoon.

Long time coming

Completion of the C-44 Reservoir and STA project has been a long time coming. In late 2004, the SFWMD hired HDR to be the designer and engineer for the entire project, Duty says. “We began the site characterization and basis of design phase in 2005 and completed the design of the 12,000-acre project as a single construction contract in 2007,” she says.

However, funding limitations led to the project being “broken into multiple smaller construction contracts to be built concurrently by the SFWMD and the (Corps),” Duty says. “During that transition and modification of project implementation based on available funding by the two agencies, HDR was responsible for updating the design so that the project could be built in steps, obtain incremental benefits, and still function as a cohesive project when all of the construction work was complete.”

Among the larger project components, the pump station was completed in April 2018 by Harry Pepper and Associates Inc., under a contract with the SFWMD, Searcy says. Bergeron Land Development concluded construction of the STA in April 2020, also under a contract with the SFWMD. The engineering firm WSP managed construction for the SFWMD.

Reservoir construction was completed by the Barnard Construction Co. Inc. in November 2021, under a contract with the Corps. “The reservoir is currently being filled and tested prior to placing the entire project in full operation, which is expected to be fall 2022,” Searcy says.

The scope and timing of the massive project presented key challenges to the design team, Duty says, as did the need to ensure project unity as it was developed in multiple phases by different contractors. “Now with the construction essentially complete, there is no evidence of individual design and construction efforts but rather one cohesive project providing water attenuation and water quality benefits to the entire South Florida and Everglades system,” she says.