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Bridges may fail in big storm

There are four bridges out of Pinellas, the only peninsular county in Florida. Could a Category 4 render all of them useless? It's possible, experts say.

By TOM ZUCCO
Published October 31, 2005

ST. PETERSBURG - Robert Weisberg tapped on the keyboard and called up the charts again. Same thing. It's always the same thing.

The computer model he designed showed a Category 4 hurricane hitting a peninsula in Florida, leaving behind two isolated islands.

On those islands are thousands of people who fled their homes to ride out the storm on higher ground. Emergency planners, worried about traffic snarls, urged them to do just that. While floodwaters recede within hours after the storm, those who stayed are stranded because the bridges to the mainland are out and the major roads are heavily damaged.

Help will trickle in by boat or helicopter in the first days after the storm. "It won't be pretty," Weisberg said.

Welcome to Pinellas, the only peninsular county in Florida.

"We could conceivably have a situation where we have two isolated parts of Pinellas, and no way of getting people off, or of getting supplies in, other than by airlifting or by boat," said Weisberg, a professor of physical oceanography at the University of South Florida's College of Marine Science.

Pinellas County's inch-thick Comprehensive Emergency Management Plan does not specifically address bridge outages, mostly because there are so many possible scenarios. The plan is designed to provide general evacuation and response guidelines.

If bridges are unsafe, Pinellas has designated points of distribution for food, water and ice that could be resupplied by overland routes or airlifts.

"It may not be exactly spelled out in the plan," said Pinellas emergency management spokeswoman Maggie Hall. "But we're aware of it.

"Our staff has worked every disaster from Andrew to Katrina and Rita. We saw what worked and what didn't."

Still, emergency managers would face a monumental challenge if Weisberg's projections come true.

Weisberg's model has a Category 4 hurricane making landfall at Indian Rocks Beach. The amount of wind and storm surge can vary dramatically depending on the direction, size and speed of the storm.

But it could create a 20-foot surge that would easily wash over parts of the Courtney Campbell Parkway and the Sunshine Skyway, Howard Frankland and Gandy bridges, Weisberg said.

Atop the surge: powerful, relentless waves.

It's the waves that do the damage, Weisberg said, as Hurricane Ivan, a strong Category 3 storm, demonstrated when it hit Pensacola last year. In its wake: rows of bridge pilings sticking out of Pensacola Bay, the remnants of Interstate 10 and U.S. 90, the main routes in and out of the city.

"I was surprised," Weisberg said. "Then I started to think about it and it made sense.

"If you keeping pounding away at the concrete with the waves, these bridge spans often get knocked over. Concrete is only three times as heavy as water, and bridges are not designed to take that pounding."

Instead, he said, bridges are designed for vertical loads - cars going on top of them. Not the horizontal pounding from mammoth amounts of water.

Most bay area bridges would be above the surge from a powerful hurricane. At their lowest points, the new spans of the Sunshine Skyway, Howard Frankland and Gandy bridges are between 21 and 26 feet above sea level, about 6 feet higher than the old spans beside them. The Courtney Campbell averages about 30 feet.

But it's the approaches to the bridges, most of which are only a few feet above sea level, that could be severely damaged or made impassable.

"Think about it: When you cross the Howard Frankland in a bad winter storm, you get water from the bay splashing up on the causeway," Weisberg said. "And that's just a bad winter storm. There were boats sitting on top of causeways after Katrina."

In a case of classic irony, those stranded in Pinellas could look to the infamously maddening U.S. 19 for help.

But parts of it and other major roads to the north might not be open.

"It's very possible for the bay to meet up with the Gulf of Mexico around Tarpon Springs," Weisberg said. "So the roadways as well as the bridges could be damaged, and that would leave the Skyway. If you could get to it."

Given the county's topography, "we could see a large concentration of people in a few relatively small places that may be inaccessible by traditional means for some time."

There is a real-life model for what could happen in Pinellas.

Last year, the eye of Hurricane Ivan came ashore just east of Mobile, Ala. But the storm saved its strongest winds for Pensacola. The two bridges over Pensacola Bay that connect the city to the rest of Florida - Interstate 10 and U.S. 90 - were heavily damaged.

Contingency plans were based on relief arriving from the north. But it was painfully slow in coming. Trucks carrying food, water, National Guard troops and power company crews had to leave I-10 near Milton and travel northwest on two-lane Quintette Road, then south on U.S. 29 into Pensacola.

They also had to compete with thousands of people trying to return home.

"We had tractor-trailer trucks on the road along with all the people trying to get back," said Janice Kilgore, Escambia County's public safety director.

So Pensacola relied partly on help from Alabama and Georgia.

"For us, it was crucial to have agreements with other states," Kilgore said. "Because of where we are, we can't always put the focus on people coming to help from Florida."

If Pinellas bridges were damaged, help would have to come from the outside, Hillsborough and Pasco primarily. But they could be dealing with extensive devastation, too.

Pinellas emergency officials say they will rely on two east-west routes in the northern part of the county - Keystone Road in Tarpon Springs and State Road 580 in Dunedin.

"Except for one section of 580 that's over a small bridge in Oldsmar, it's all over land," said Hall, the Pinellas emergency management spokeswoman. "There shouldn't be the gridlock you see day to day. Most everybody will be off the road."

Although the odds of a hurricane wiping out all four Pinellas bridges is remote, it's not impossible.

The surge from a storm like Katrina likely would have "a significant impact" on the low-level approaches to the Skyway and other local bridges, said Pepe Garcia, structures and facilities engineer for the Florida Department of Transportation.

The extent of the damage would depend on wind speed, water volume and the angle at which the storm hit the bridges, Garcia said.

"Bridges aren't designed to withstand worst-case scenarios," Garcia said. "We couldn't afford them if we designed that way.

"You have to ask if it's possible for all the worst-case scenarios to happen at the same time, and, yes, it is possible. Is it probable? No, but there are no guarantees."

In the end, it's a calculated risk.

"Will bridges in Tampa Bay be built such that they'll survive at any cost? That's a decision that may come in the future but wasn't looked at in the past.

"We're very sensitive to cost, but also how the public needs to be served."

DOT officials say the newer spans of the Skyway and the Howard Frankland were built higher than the bridges that went out in Mississippi and Louisiana during Katrina, and that the extra height will make a significant difference in their ability to survive a major storm.

"This is an evolving process," Garcia said. "It happened after (Hurricane) Andrew with the new building codes and after Skyway went down and was rebuilt."

In the meantime, Garcia said, post-hurricane efforts will focus on repairing, rather than replacing, what's been damaged.

"How can we restore the roads and bridges, and how quickly?" Garcia said. "That's the name of the game."

Back at his computer, Weisberg watched the water rise and Pinellas County turn into a pair of barrier islands.

"This is a possibility," he said, "that needs to be thought about."

[Last modified October 31, 2005, 05:16:45]