Concrete pyramids are Audubon of Fla.'s erosion-control vanguards

Trees where brown pelicans and other colonial birds constructed nests just last spring now lay dead and dying along Sunken Island’s shoreline in Hillsborough Bay.

They are victims of erosion caused by passing freighters, barges, cruise ships and storms.

And because Sunken Island is part of the Alafia Banks Bird Sanctuary — nesting grounds for 16 species of birds, including rare American oystercatchers, reddish egrets and roseate spoonbills — the erosion is cause for concern.

After several years of planning, designing and permitting, Audubon of Florida has nearly completed what it hopes will be a solution to the problem.

Eight rows of heavy armor, shaped like porous pyramids, now flank a portion of the island. They act as breaks to absorb the power of the waves, which build like mini-tsunamis before crashing into the shoreline.

The $315,000 project, funded through a grant from the Pinellas County Environmental Fund and a donation from Mosaic Fertilizer, which owns the island, should be complete this week.

“To see this come together is cause for dancing in the streets,” said Ann Paul, regional coordinator for Audubon of Florida. She oversees Audubon’s Florida Coastal Islands Sanctuaries.

This is not the first attempt at controlling heavy erosion on the island. In the 1980s, when the state-of-the-art erosion control method called for tying together old tires and pushing them into the sand, Audubon did just that.

But 30 years later, the strapping is dissolving and the tires must be removed, Paul said. And the banks continue to erode at a rapid clip.

The 8,100-pound, 5-foot-tall concrete pyramids should last 100 years, maybe more, said Tom Brown, chief executive officer of Living Shoreline Solutions, which designed the wave breaks.

“We’ve been through Category 4 and Category 5 hurricanes with these things (in other locations) and they haven’t moved,” Brown said.

Brown pelicans, Forester’s terns, little blue herons and least terns stood on the island nearby as Brown explained how the waves will hit what he calls “wave attenuation devices,” absorb their energy, then release the water to a calm shoreline.

An added bonus will be sand trapped by the pyramids that could then help rebuild the island’s rim.

“We’re pretty excited about this,” Paul said. “The reason we invested all the time, energy and money is because this is one of the most important bird nesting sites in Florida.”

Most of the 75-acre spoil island remains intact, but losing trees along the shoreline means losing some of the most sought-after nesting habitat for birds like the brown pelicans, she said.

If the project works out as planned, Paul said, Audubon will likely work to raise $1 million more to place the same kind of wave breaks along other parts of the island.

http://www2.tbo.com/news/community-news/2011/oct/31/menewso1-concrete-pyramids-in-hillsborough-bay-cou-ar-299465/

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