Frances poses a threat of flooding in Florida

Storm surge could cause deaths, severe damage

Hurricane Frances

September 04, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

As if the winds weren't enough bad news, hydrologists told anxious Floridians yesterday that water - pumped by Hurricane Frances from the ocean and the sky - could pose an even more serious threat to their lives and property.

A storm surge of up to 12 feet during two high-tide cycles this weekend could submerge up to a third of the barrier dunes north of storm's center and batter beachfront homes, they said.

Worse, as much as 18 inches of rain is forecast for Central Florida over at least two days - adding more woes to a state already soggy from two to three times its normal rainfall in August.

"This is only going to add to an already existing problem. ... There is going to be a lot of flooding," said Harry Lins, a hydrologist with the U.S. Geological Survey, in Reston, Va.

The Southeast River Forecast Center said that river flooding was "likely" in a band from Jacksonville to Palm Beach, and extending from the Atlantic to the Gulf of Mexico.

The South Florida Water Management District went to emergency operations this week and raced to pump as much water as possible from the water-management lakes and canals that lace much of the flat, swampy state.

Even so, "when we get greater than a foot of rainfall, chances are pretty good that some areas that are not able to handle that much are going to see some flooding," said district spokesman Randy Smith.

Although a hurricane's high winds provoke the most fear, storm surges and inland flooding usually claim the most lives. High winds collapse buildings and kill people, Lins said, "but not with nearly the frequency with which people get swept up in floodwaters." Usually, he added, it's while they're driving.

It won't take much rain to flood roads in Central Florida. The place has been inundated - not just by Charley, but also by torrential summer thunderstorms. Rivers in west central Florida are at or near record highs. Standing water is everywhere.

"Many parts of the state may have the appearance of being one big lake," Lins said. With another foot of rain, people whose homes were built in slight depressions will find themselves in 2 to 3 feet of water.

Last year, a storm that delivered 18 inches of rain in three days - a pattern close to some forecasts for Frances - left behind the worst flood on record in an inland area near Sarasota, said Richard L. Kane, hydrologic data chief for the USGS Center for Coastal and Watershed Studies in Tampa.

"We had 119 homes damaged, and you had some people who were killed in traffic accidents," he said. "Damage estimates were in the neighborhood of $10 million to $20 million."

On Florida's Atlantic barrier beaches, and on the mainland across the coastal bays, the water hazard will be the storm surge - ocean water piled onto the shore by the hurricane's winds.

The USGS in St. Petersburg predicted yesterday that if Frances remains a Category 3 storm when it finally makes landfall today, the storm surge could reach 9 to 12 feet.

In East Central Florida, that's enough to inundate up to 35 percent of the barrier dunes, according to USGS oceanographer Asbury H. Sallenger Jr. A Category 4 storm surge could swamp 49 to 78 percent of the dunes.

That stretch of beach includes some undeveloped sections but also has many with cottages and multi-story buildings - all on barrier islands like Maryland's - no wider than 500 yards.

Where the storm surge brings the ocean over the dunes, many structures are in peril. A 9- to 12-foot surge would be topped by breaking surf of similar height.

"Anything, if it's a ground-level structure, will be severely battered," Sallenger said. Homes on pilings built to modern standards would likely survive. However, older places with inadequate pilings would likely be lifted up or cut down by the waves. The debris could then pound other structures.

"In the larger buildings, the first- and second-floor windows could be battered through by the waves and flooded," he said.

The beaches and dunes, meanwhile, could lose 7 feet of height to erosion, and sand carried by the water might pile up against homes farther back from the beach, crushing, or partly burying them.

The mainland is also at risk. Seawater blown over the dunes or through the inlets can fill the coastal bays "like bathtubs," and wind would push the water up against the mainland shore, Sallenger said.

As Charley approached last month, forecasters feared winds could build up a 30-foot storm surge at the north end of Tampa Bay. However, Charley moved quickly past before that happened.

"What's scary about Frances is ... they estimate it's going to slow down close to landfall. That gives more time to build up the surge," Sallenger said. The water would run up onto the land and up into coastal rivers and bays, causing more flooding.

Even when Frances finally pulls out of Florida, it won't be wrung dry, Lins warned.

After Hurricane Camille finished pounding the Mississippi Gulf coast with its Category 5 winds and storm surge in 1969, it tracked north, then east across the Appalachians.

There, it unloaded more than 25 inches of rain on Nelson County, Va. The torrent loosened the mountain topsoil in a landslide that killed about 150 people.

"Storms that move up the Appalachians like this with enormous amounts of precipitation are always a hazard," he said.

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