By Shelby O. Mitchell
The South Florida Water Management District is undertaking an unprecedented state-federal initiative to restore its own national treasure: the Everglades. The agency, which oversees resources in the southern half of the state, is restoring nearly half the wetlands and floodplains that have been destroyed by 6,000 manmade water-control structures.
Stormwater Treatment Areas are a crucial part of the district's plan. Mandated by the state's Everglades Forever Act in 1994, these are areas of farmland reclaimed to control excess nutrients. Since then, 40,000 acres have been converted into treatment wetlands and phosphorous levels have fallen 85%. The $1.5-billion effort is funded by farming and property taxes and certificates of participation similar to municipal bonds.
The district builds and maintains structures — a dozen pump stations, 200 control structures, and 100 miles each of levees and canals — that control water levels and protect the recreated wetlands. Strategically placed box culverts allow water to flow under elevated roads and berms.
Engineers have used both cast-in-place and precast concrete conduits, but discovered the precast design allowed gaps where flood gates were attached. “Now wherever we install a gate, we use cast-in-place culverts for more consistency and to reduce sediment transfer that can cause collapses,” says Jeffrey Kivett, P.E., engineering and construction bureau chief for the district's Operations, Maintenance, and Construction Division.
In one area 70 miles west of West Palm Beach, the contractor used a Box Culvert Traveler form. The system, composed of Doka USA Ltd.'s Frami formwork, enabled the contractor to cast 300-foot culverts in 50-foot sections 8 feet tall and 8 feet wide. The modular system allows limitless configurations: Panels can be used vertically or horizontally and combined to fit job requiremens within 6-inch increments.
Contractors usually build cast-in-place culverts by pouring the walls and decks in separate phases. With the traveling form, they put the formwork into place, set the rebar, and cast the entire concrete shell in a single pour. Once the form is removed, it can be rolled into place for the next pour in less than a minute.
The process helped contractors keep the time-sensitive job on schedule. “There are a lot of costs associated with placing culverts,” Kivett says. “You have to pump to keep the ground-water down, and the timing of opening up the hole is critical. The quicker you can get it done, the better.”