Bay Area Has Safeguards To Control Storm Surge

TAMPA - Watching New Orleans residents break holes through their roofs in frantic attempts to climb above floodwaters, it's hard not to wonder: Could it happen here?

Engineers say that a flood similar to the one that drowned New Orleans is unlikely. The reason is that much of New Orleans was built below sea level, in a massive bowl surrounded by water. The city flooded when two levees breached, allowing water to flow into the bowl from the 628-square-mile Lake Pontchartrain.

Levees in the Tampa Bay area don't play as crucial a role in protecting Bay area cities as those in New Orleans. Bay area levees are adjuncts to other flood-control structures.

The prime example is the Tampa Bypass Canal. The U.S. Army Corps of Engineers built the canal after Hurricane Donna caused flooding here in 1960. The corps finished the first section of the 13.1-mile project in 1968.

The final section, where the Hillsborough River crosses north of the canal near Fletcher Avenue, was completed in 1983. The Southwest Florida Water Management District can close canal gates and route potential floodwaters from the Hillsborough River around the cities of Tampa and Temple Terrace, then into McKay Bay.

"What they're trying to do [in New Orleans] with the levees is keep water out of the city," said Gary Kuhl, director of operations for the water management district, known as Swiftmud. "We're routing waters around the cities," Kuhl said. "I don't think we have anywhere near the concerns."

Make no mistake: A Category 4 hurricane like Katrina with a 20-foot storm surge would cause widespread flooding anywhere on the west coast of Florida. Hurricane evacuation maps show that flooding from a Category 4 or 5 would engulf wide swaths of land several miles inland in the Bay area. The storm surge would push water up rivers, flooding adjacent land 10 to 12 miles from the coast.

"If you get 20-foot storm surge in the Bay, you're going to have 20-foot storm surge in the river," said Rob Teegarden, acting director of the Tampa Water Department.

1933 Hurricane Did Damage

The Hillsborough River Reservoir Dam, just east of Temple Terrace between Fowler Avenue and Busch Boulevard, supplies drinking water to city residents. In 1933, a hurricane washed away a dam in the same place. Teegarden said he's not worried about that happening again because engineers can control the water's elevation behind the dam.

"We have 22 feet elevation of water on one side pressing against 20 feet [of storm surge] on the other side," he said. "You have to have unbalanced forces to wash the dam away."

Likewise, water district engineers are not concerned about a monster storm surge disabling the locks and weirs that make the Tampa Bypass Canal an effective flood control structure. During the past two years, the agency spent $1.7 million repairing and refurbishing all the gates on the canal. Most of the gates are now computer-operated, Kuhl said, so they don't "have to send somebody out there in 120 mph winds to crank a wheel in gate."

Storm Surge Will Recede

In a Category 4 scenario, Kuhl said he would open the gates on the canal, allowing the storm surge to move upstream, its power diminishing as it moves inland. Grassy levees, more than 20 feet above sea level, would contain any overflow, said Dale Ravencraft, Swiftmud's structure operations manager.

"A 20-foot storm surge would be up in here, but it wouldn't top the levees," Ravencraft said while standing at a series of weirs on the canal between Fowler Avenue and Harney Road.

After the storm surge recedes, water district officials would close a dam north of Fletcher Avenue, routing most of the water from the Hillsborough River into the bypass canal. Last year, during rain from Hurricanes Frances and Jeanne, the canal was moving about 6 billion gallons of water a day through the main lock at Trout Creek Park. The canal prevented major flooding on the river.

The agency also has a 600-acre reservoir on the Little Alafia river that can drain floods from 19 square miles. The reservoir lessens flooding on the larger Alafia River.

There are no flood-control structures on the county's other large river, the Little Manatee.

Hurricane maps show a Category 4 storm would cause flooding along the river south of Ruskin and well inland.

Residents in eastern Hillsborough County don't have to worry about flooding from the C.W. Bill Young Reservoir, even in a Category 4 storm, said Mandi Rice, an engineer with Tampa Bay Water.

Nothing Like Pontchartrain

The 15-billion-gallon reservoir is not part of any other waterway, making it easier to control water levels. No storm surge could wash over the reservoir's embankment, which rises to 145 feet above sea level, Rice said.

"Our facility is very different than Lake Pontchartrain," Rice said. "That's an extremely large facility, but it's also tidally influenced: It's connected to the Gulf of Mexico."

Engineers think one of the reasons the levees broke in New Orleans is that winds from Katrina, sweeping down from the northeast, pushed waves toward the levees. Rice said wave intensity is a function of the wind's velocity and the distance it travels across a water body's surface.

"Our facility has a maximum length ... of two miles," she said. "Lake Pontchartrain is 40 or 50 miles."

A year ago, wind-driven waves from Hurricane Frances punched a hole in the berms atop a phosphogypsum stack at Cargill Crop Nutrition in Riverview. More than 60 million gallons of polluted water flowed into a stream leading to Hillsborough Bay.

Cargill, now called Mosaic Co., spent $30 million to improve water storage and treatment at the plant. Three ponds capable of holding more than 500 million gallons will act as a safety valve to low water levels in the 1 billion gallon stack if another storm hits.

Reporter Mike Salinero can be reached at (813) 259-8303.