About the author: Guillory is a vice president and division manager with PBS&J and project manager of the Ten Mile Creek project. He may be reached at 561/689-7275 or by e-mail at [email protected]. Arrieta is a senior civil engineer with the South Florida Water Management District and served as project manager for the Ten Mile Creek Project. She may be reached at 561/682-6758 or by e-mail at [email protected].
Blake Guillory, P.E., and Denise Arrieta, P.E.
undefinedExperience teaches that every big problem can be broken into smaller, manageable tasks. Within the Comprehensive Everglades Restoration Plan (CERP), considered the largest environmental restoration initiative in history, are myriad projects, each designed to bring America’s Everglades closer to its natural state.
One of those projects is already nearing completion. The Ten Mile Creek Water Preserve Area, a freshwater reservoir and wetland storm water treatment system, will serve as a prototype for larger reservoir projects integral to Everglades restoration.
Immediate benefits
The Everglades once held large amounts of fresh water collected in the rainy season. To prevent flooding, this valuable freshwater reserve is now often diverted to coastal estuaries. These large inflows of storm water runoff can disturb the delicate balance of the estuaries by changing the salinity during critical periods.
The Ten Mile Creek project was authorized by Congress under the Water Resources Development Act of 1996 (WRDA 96) as a Critical Restoration Project. To receive this designation, the project had to demonstrate it could provide immediate, independent and substantial environmental benefits to the Everglades. That is, the projects’ size and design would offer a relatively short launch period yielding quick, noticeable, positive results.
Upon completion, the freshwater reservoir at Ten Mile Creek will be one of the first restoration projects designed to recapture and enhance water storage capability for the benefit of the ecosystem. An adjacent created wetland, serving as a storm water treatment system, will improve the creek’s water quality, and, ultimately, restore balance to surrounding ecosystems affected by the current high flows of storm water.
Endangered lagoon
Ten Mile Creek is located seven miles southwest of Fort Pierce, Fla., in St. Lucie County. The small, tree-lined creek, one of the St. Lucie River’s five tributaries, conveys an estimated 150,000 acre-ft of storm water flow annually providing nearly 25% of flow to the river’s North Fork.
The St. Lucie River feeds nearby Indian River Lagoon. This 156-mile-long lagoon, designated as an Outstanding Florida Water, is one of the most biologically diverse estuaries in the U.S. Nearly 3,000 species of animals and over 1,300 plant species make the lagoon their home. Among the inhabitants are 32 endangered species including the red cockaded woodpecker, bald eagle, peregrine falcon and several types of sea turtles. Most notably, one-third of the nation’s West Indian manatees, also an endangered species, live in Indian River Lagoon.
The lagoon offers significant economic benefits to the region as well through commercial fishing, recreational use and shellfish harvesting. Half of east Florida’s clams, and 15% of the country’s clam harvest, come from the lagoon. Thousands of jobs and millions of dollars in state income rely on the health of Indian River Lagoon.
The current influx of fresh water threatens the lagoon’s ecosystem and economy. By capturing and storing storm water discharges from Ten Mile Creek during the rainy season, the amount of fresh water discharges and sediments entering the St. Lucie River Estuary and, ultimately, Indian River Lagoon will be more manageable.
Natural solution
The Ten Mile Creek Project, a joint effort of the U.S. Army Corps of Engineers and its local partner, the South Florida Water Management District, is designed to capture and treat a portion of the summer storm water flows from Ten Mile Creek to the North Fork of the St. Lucie River. This, in turn, will improve the creek’s water quality and help to facilitate improvements in the balance of the Indian River Lagoon.
When work to create the Ten Mile Creek Water Preserve Area is finished, water managers will be able to divert storm water into a 550-acre aboveground reservoir offering a storage capacity of 2 billion gal. A station with three pumps, with a total capacity of 380 cu ft per second (cfs), provides flexible water lifting for the project during a variety of high-flow conditions in the creek. Once in the reservoir, suspended sediments will settle as the water moves through the system. Water in the reservoir will then be passed into an adjacent storm water treatment area via a gravity control structure. When gravity flow from the reservoir to the treatment area is not possible, a second 40-cfs pump station will allow water managers to meter the flow of water from the reservoir to the wetland treatment system through a 50-ft-long, 11-gate distribution structure. The distribution system is designed to simulate an 18-in.-deep sheet flow of water through wetlands. The wetland treatment system will improve water quality by filtering out excess nutrients from storm water before it enters the St. Lucie Estuary and Indian River Lagoon. The consulting firm of PBS&J provided project design services and assistance during construction for this $30 million project.
The project was funded by the South Florida Water Management District and the U.S. Army Corps of Engineers as a 50/50 cost share. Atlantic-Skanska Inc. is the prime contractor for the construction of the reservoir and storm water treatment area along with the associated pump stations and control structures.
Additional benefits
In addition to improving storm water quality, supporting the ecosystem and maintaining flood protection, the project also enhances available water supplies. When needed, an existing water-control structure downstream of the project will allow water managers to release excess untreated water from the reservoir back into Ten Mile Creek to supplement agricultural demands during the dry season. This will alleviate stress on the Floridan Aquifer, the current source utilized during the dry season.
Another bonus of this project has been the collaborative efforts between the South Florida Water Management District and St. Lucie County to develop portions of this site into a natural preserve area yielding recreational opportunities for hiking, wildlife viewing, canoeing and fishing along the oxbows of the creek and surrounding scrub areas.
Ten Mile Creek is considered a prototype for similar projects up to 20 times its size. The project’s design phase has already provided valuable lessons for future reservoir projects.
For example, reservoir depth was optimized to avoid creating waves and resulting bank erosion during storms. Engineers also chose soil cement over rock for the reservoir’s interior levee protection resulting in a significant cost savings. During the construction phase, cost-effective methods of handling the millions of cubic yards of material for this project, and future restoration projects, were identified.
The project is scheduled for completion in September, just under two years after breaking ground. System tests and monitoring at Ten Mile Creek and the adjacent preserve will begin in fall 2005. The lessons learned from Ten Mile Creek will save time and money, and will yield greater benefit, for future CERP projects.
