GAINESVILLE --- Other states aren't so lucky, but when beachgoers in Florida dig their toes in the sand this summer, they may be glad to know many of the state's shores are in little danger of washing away -- and some are even getting larger.
Contrary to popular perception and the trend in most other states on the East Coast, Florida's beaches generally are not falling victim to coastal erosion or steadily rising sea levels, a new University of Florida study has found. In fact, despite areas of serious erosion, east coast beaches are actually experiencing an average increase in size. Beaches on Florida's west coast are remaining about the same size on average, the study found.
"I think it leads to cautious optimism," said Bob Dean, a UF coastal engineering professor and the lead investigator in the study. "The sky is not falling -- not right away, anyway. And we should consider our state to be unique in this respect."
Dean and several graduate students analyzed available historical and recent shoreline measurement data in Florida's 24 counties with sandy beaches, including 12 on the Gulf coast and 12 on the Atlantic coast. Measurement records dating back at least a century were available for all counties.
The researchers, who used the data to create an atlas outlining the shoreline change for each county, discovered "a lot of surprising things," Dean said. Among the most significant of their findings is that beaches on Florida's east coast are increasing in size on average at the rate of about 4 inches each year, he said.
In contrast, beaches in other Atlantic states are shrinking or disappearing on average, some very quickly, Dean said. For example, Virginia's coast retreats as much as 10 feet annually, he said. Only one other Atlantic state -- New York -- is experiencing a similar average net gain in its beach sizes, Dean said.
Dean said a couple of factors have led to Florida's special predicament. For one thing, suspended sand in the water travels in a southerly direction along the Eastern Seaboard because of currents generated by predominantly northeasterly waves, making Florida the natural repository of sand from erosion in more northern states, he said.
But a more complex process also could be at work, Dean said. Before the recent period of sea level rise -- a process that started about 20,000 years ago -- the continental shelf off of the East Coast was the repository of sand from the many rivers that empty into the Atlantic. During more recent times, sea level increases at the rate of about 10 to 12 centimeters per century have resulted in waves pushing this sand ashore onto East Coast beaches.
Dean said wave energy is higher in the northern Atlantic states than in Florida, and he speculated those states already had exhausted their offshore sand deposits.
"Since we have low wave energy in Florida, it's taking a lot more time to drive the sediment back in to our beaches," he said.
Many communities in Florida have added sand to their beaches through beach renourishment projects. Dean said Atlantic beaches would have increased in size without renourishment, but it has had a beneficial effect. Over the last 20 years, east coast beaches have widened, on average, approximately 1.5 feet per year, a result of an estimated 40-45 million cubic yards of sand moved onto beaches in renourishment projects, he said.
While the trend for Florida's east coast may be expanding beaches, some are eroding rapidly, particularly those located near man-made inlets such as St. Lucie Inlet, Dean said. Inlets lead to erosion partly because jetties and deep channels disrupt the normal southerly flow of sand, and partly because inlets carry sand away from beaches.
"Having an average shoreline that's in good shape doesn't mean the whole shoreline is in good shape," Dean said. "There are a lot of places that are in pretty serious condition in terms of erosion. My estimate is 80 to 85 percent of that erosion is caused by inlets."
Dean's study was part of a larger project funded by a three-year, $180,000 grant from Florida Sea Grant.