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DREDGED MATERIAL: by Victoria Parsons It's a two-edged sword. Dredged materials from Tampa Bay's ports and shipping channels can be used to create habitat like manmade islands that provide nesting sites for endangered and threatened birds, protect beaches from further erosion or fill mined areas in and near the bay so they support wildlife again. But when it accumulates at a rate of approximately a million cubic yards per year -- enough soil and silt to fill Raymond James Stadium to the top 10 times -- finding beneficial uses isn't always possible. And unless bay managers continue to expand spoil islands and come up with innovative ideas for dredged material, the region may run out of environmentally safe, cost-effective options within the next five years. Since 1999, all material from federal projects in the Tampa Harbor has been used in beneficial projects, says Tim Murphy, project manager for the U.S. Army Corps of Engineers in Tampa Bay. "Beneficial uses are not accidents. They require an inordinate amount of coordination with the public and resource agencies to make them work. All have been great successes, but all have been difficult to initiate."
One of the challenges to beneficial uses, says Murphy, is that the Corps is directed to find the "least-cost environmentally acceptable" option for disposing of dredged material and transporting spoil can often become the most expensive factor in a dredging project. Another is the fact that most Tampa Bay dredged material is not suitable for beach re-nourishment. "The DEP (Florida Department of Environmental Protection) has very detailed requirements for beach sand, including color and fineness," he said. "Most of what we dredge in Tampa Bay does not meet those requirements." The exception to that rule was 600,000 cubic yards dredged from Bayboro Harbor and placed at Egmont Key. "We had support from Senator Bob Graham and Governor Jeb Bush to make that happen because they recognized the need to protect an island that's both environmentally and historically valuable," he said. Unlike most Tampa Bay dredged material, it was more sand than silt, he adds. Other beach-quality dredged material may be removed from Pass-A-Grill and Johns passes. Additionally, the Corps is considering "re-mining" materials already in spoil islands if they are suitable for beach renourishment. Dozens of holes hold promise One of the most important uses for materials from maintenance dredging may be filling manmade holes dug for sand or fill material. The Tampa Bay Estuary Program is spearheading an effort that recruits local fishermen to assess habitat value in 10 holes dug prior to 1980. "The concern is that some of the holes may provide important winter refuges for cold-sensitive sports fish such as snook, which hunker down in them because deep water is warmer," said Holly Greening, senior scientist at TBEP. "The other side of that picture is that deep water with minimum flushing seldom has sufficient oxygen to support fish and other wildlife during warmer months." The "fishing for science" initiative asks fishermen from local angling clubs to sample 10 holes on a regular basis over a 12-month period, and record the number and species of fish they catch. Holes that are shown to be effective habitat will be left alone, but others may become sites for habitat restoration using dredged materials. The research initiative began after a pilot project completed in 2001 placed 400,000 yards of dredged material in a 76-acre hole off MacDill Air Force Base. "One of the reasons we selected that site is because it's near a deep-water channel so fish had somewhere to go," Leeser said. "Plus, if you look at an aerial photo, you can see evidence of erosion around the edge of the hole, so we were losing more seagrass habitat as the sides fell in. Filling the hole might slow or stop the erosion and improve habitat in and around it." Another beneficial use the Corps is considering is re-creating longshore bars in areas where tidal flows may be restricting seagrass growth. "Those bars have eroded over the years, and building berms would help protect seagrasses from waves and wakes," Murphy said. Like all of the beneficial use projects the Corps has undertaken, the concept for longshore bars came from local environmentalists. "We are committed to restoring longshore bars in partnership with the Tampa Bay community," Leeser said. Helping to restore habitat Along with saving capacity in disposal areas and restoring important habitat, finding beneficial uses for dredged materials offers financial rewards for Tampa Bay residents. That's particularly clear in Cockroach Bay where recreating a series of habitats in an abandoned shell pit. "It will take hundreds of thousands of cubic yards to fill the pits," says Dr. Brandt Henningsen, senior environmental scientist with SWFWMD's Surface Water Improvement & Management (SWIM) program, "but it won't cost taxpayers a penny for the first 300,000 cubic yards." If fill material was purchased, it could cost as much as $15 per cubic yard, Leeser adds. Working closing with Murphy, Henningsen hopes to see 300,000 cubic yards of dredged material from an Alafia River maintenance project placed in the shell pit by the end of the year. The Corps also has submitted a request for additional funding to cover the incremental costs of placing material from the Port Manatee expansion at Cockroach Bay. The 70-acre shell pit is currently 12 to 15 feet deep with very little aquatic life. With up to a million cubic yards of dredged material - depending upon final design plans - the shell pit would be transformed to a series of habitats, from salt marsh and mangroves to shallow estuarine areas that serve as fish nurseries. "We'll be able to redirect freshwater discharges from Hunter's Lake to drive a salinity regime that allows us to create different habitat opportunities," Henningsen said. "A series of meandering tidal channels will ultimately connect to mosquito ditches cut in the 1960s, so seagrasses will be recruited in the lagoons and channels." When the cost of transporting dredged material to approved disposal areas or beneficial use projects is equal, local partners receive the material at no charge, explains Buddy Copeland, the Corps' continuing authorities program manager for the Jacksonville district. When the cost is higher, federal law requires that the Corps find local partners to cover 25% of the difference between traditional placement and beneficial uses. At Cockroach Bay, local funds will come from penalties paid by Gardinier Co. after an acid spill in the Alafia River. The funds, still pending final approval, are available through recent legislation that provides grants that cover the additional costs that may be incurred with beneficial uses of dredged material. "This is one of those programs where the whole Tampa Bay region benefits," Copeland said. "The first restorations at Cockroach Bay already are showing results, and this is another major piece in that puzzle."
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Still, the Corps hopes to find beneficial uses for more than 25 million cubic yards of dredged material over the next 25 years. "That figure is a very rough estimate because one of the biggest issues is identifying sites where beneficial uses might be possible, then gathering data on the site and determining how much material the site might take," adds Tracy Leeser, a planning technical leader for the Corps.