Wave barriers promise erosion control for wading bird habitat
“We’re excited finally to be in the installation stage.”
GIBSONTON — From long-legged herons to colorful spoonbills to darting oystercatchers, some of Florida’s rarest, endangered, iconic wading birds begin their lives on Tampa Bay’s spoil islands here.
Each spring, their parents return to small and heavily overgrown spits such as Sunken Island near the mouth of the Alafia River to share their designated retreat in general harmony with abundant rats and rattlesnakes as they nest, hatch and rear offspring.
Audubon’s Richard T. Paul Alafia Bank Bird Sanctuary in the Hillsborough Bay estuary is the most important wading bird colony in the state, according to Florida’s Fish and Wildlife Conservation Commission. Hosting at least 18 species, it is considered the most diverse of such colonies in the continental United States.
Yet, for some of those species, the numbers have been dwindling year after year. Population declines are being noted for the showy Snowy Egret and the graceful White Ibis, said Ann Paul, Audubon of Florida’s regional coordinator. The Little Blue Heron, a tree-nester, is a “species of special concern. The Least Tern has been driven to “threatened species” status by human development of the beaches it favors for nesting. The increasingly rare American Oystercatcher, feathered in black and white with a large orange-red bill, now is listed as a “special concern” as it tries to hold on in Hillsborough Bay.
Even there, though, habitat is at risk; the island shorelines eroding, gradually but consistently washed away by the constant wave action generated through the wake of passing commercial and pleasure boats, in the process taking trees needed for roosting and dissolving sandy beach required for feeding.
Sunken Island, for example, lays on a general east-west alignment immediately south of the Alafia River channel, which branches to the east from the main north-south Tampa Bay ship channel. Through this channel passes the freighter and barge traffic arriving and departing the Mosaic phosphate processing plant docks, as well as numerous smaller pleasure craft coming from or motoring farther up river.
This week, however, a project aimed at halting the erosion by blocking and redistributing the wave action is being completed around the northern face of the oblong island. The “wave break” consists of eight arrays of large, pyramid-shaped concrete “wave attenuation devices” (WADs) installed in corner-to-corner sections just offshore. When complete, the WADs will stretch for 775 linear feet, creating a settled offshore reef both calming wave action and enhancing the food chain.
Each pyramid, 10 feet across at the base and weighing 5,000 pounds, is a stable barricade able to withstand the heaviest of seas, noted Tom Brown, CEO of Living Shoreline Solutions, the Dade City-based company which designed the system.
The firm has installed 16 such systems in water bodies around the world and “not one of them has failed yet,” Brown added.
The acid-neutral concrete structures are hollow with perforations on the slanted sides that allow small fish and crustaceans to enter or pass through and encourage oysters, barnacles or other marine life to attach, thereby creating a sea life nursery in much the same way naturally-growing mangrove roots and sea grasses do. Pyramids facing the shipping channel also are horizontally grooved on their outward flat sides to further interrupt and redistribute the energy of ship-wake or storm-driven waves slapping them.
The project has been years in the planning, design and engineering, permitting and then funding stages, said Mark Rachal, an Audubon field biologist. “We’re excited finally to be in the installation stage,” he added.
Financial support for the $315,000 project has come from a combination of grant monies obtained through the National Fish and Wildlife Foundation plus grant-matching funds provided by Mosaic, Tampa Electric Company, CF Industries and other donors to Audubon’s Florida Coastal Islands Sanctuaries program. Mosaic owns the islands that comprise the bird sanctuary and leases them to the National Audubon Society for its management, said Christine Smith, the phosphate giant’s Florida headquarters spokesperson.
It is expected now, Paul summed up, that the trees the Brown Pelicans and White Ibis and Roseate Spoonbills need for their nests will be protected and preserved, sturdily waiting for them come the spring breeding season, and that the oystercatchers will find plenty of nest-inviting sand above the high tide mark.
Copyright 2011 Melody Jameson