Beach renourishment predictions “reasonably” accurate, study finds

April 20, 2001

GAINESVILLE, Fla. — Coastal communities considering spending millions on renourishing beaches often want assurance their investment won’t wash out with a few big storms.

The results of new University of Florida research may be a step toward that goal.

In the first study of its kind, the research compared the predicted and actual performance of beach renourishment projects in Florida. Although critics have said it’s impossible to predict the fate of such renourishment projects, the study concluded the method used in the predictions has “reasonable” accuracy, said Bob Dean, a UF professor of civil and coastal engineering and the chairman of the coastal engineering technical advisory committee in the state’s Office of Beaches and Coastal Systems.

“I think it will provide some confidence to officials embarking on renourishment projects for their communities, although we would like to do better,” Dean said.

Florida spends about $90 million annually on beach renourishment projects, with local municipalities and the state and federal governments each contributing about $30 million. Another $100 million is devoted to beach renourishing nationwide, Dean said.

The average project to renourish about three miles of beach is about $15 million. Because of the hefty price tag and the criticism that often accompanies it, officials would like to have sound predictions as a basis for their decisions.

For the study, Dean compared the predicted and actual performance of renourishment projects at eight beaches in Florida, some dating back a decade, based on one of two most frequently used methods. The projects were at Manatee, Martin and St. John’s counties, Longboat Key, Captiva Island, Juno Beach, Ocean Ridge and Key Biscayne.

The researchers found the method predicted the amount of sand remaining on the beach to within an average of about 30 percent — meaning at worst it would predict 30 percent more or less sand than actually remained after a given period, such as a year.

As for the size and shape of the beach, the predictions produced figures that were within about 50 percent of the actual outcome.

It’s not a particularly high accuracy rate. But Dean said the study shows the method is a good first step, especially considering the difficulty of accounting for the impact of storms, currents, sand movement and other often unpredictable elements of beaches.

“If you look at beaches, you’ll find certain areas such as erosional hot spots behave differently than others,” he said. “There are a lot of things we don’t understand about beaches.”

Dean said the study adds to an emerging body of knowledge about beach renourishment that is slowly giving planners better tools to assess renourishment projects. Such predictions are vital to planning because of the high cost of renourishments, he said.

Dean presented his findings last week at the Geological Society of America’s southeast section regional meeting in Raleigh, N.C.