GALVESTON, TEXAS Seawall offers scant protection

The water has a drainage path, so it won't remain on the island.
KNIGHT RIDDER NEWSPAPERS
FORT WORTH, Texas -- Galveston's massive seawall offers little protection to the thousands of Texas homes and businesses sitting behind it if Hurricane Rita slams into the barrier island.
If Rita makes landfall as a Category 5 storm, it could produce a storm surge at least as high as 22 feet, which would easily overtop Galveston's 17-foot-high, 10-mile-long seawall, experts say.
Perhaps worse, the back of the island isn't protected by the seawall and sits at a much lower elevation, meaning that it would flood as the Gulf of Mexico rises.
"It will inundate the entire city," said Don Van Nieuwenhuise, a geologist at the University of Houston. "The whole island will be under water."
The good news is that Galveston would not remain flooded for long, said Danny Reible, an environmental engineer at the University of Texas at Austin.
That's because after the seawall was built after a hurricane in 1900 that leveled the city and killed 8,000 people, houses and business behind the wall were raised as much as 20 feet.
Bowl effect
The city actually slopes down gradually from the Gulf of Mexico toward West and Galveston bays. That would spare it the fate of New Orleans, which sits in a kind of bowl below sea level.
When the levees in New Orleans broke, the floodwaters had nowhere to drain, leaving portions of the city submerged more than three weeks after Hurricane Katrina slammed into Louisiana.
"Certainly, if you have a 25-foot storm surge going over the seawall, it will cause serious damage," Reible said. "But the amount of water that would overtop that 17-foot wall will have a natural path for drainage. You wouldn't have the problem of the city filling up with water and staying there."
Everything depends on where the storm hits.
Projections late Wednesday showed Rita landing just southwest of Galveston. But the massive hurricane would create a storm surge stretching for miles along the coast.
And Texas is particularly vulnerable to storm surge, said Steven DiMarco, an oceanographer at Texas A & amp;M University.
The reason: The Gulf floor slopes gradually downward from the shore into the Gulf, allowing the storm surge to build up higher than it did off the coasts of Louisiana, Mississippi, Alabama and Florida, where the floor drops steeply near shore, DiMarco said.
If the storm surge is as high as projected, 10 feet of water would race over the seawall and smash through the city.
"The moving water would have mass, and basically it would probably flatten weaker structures," said Steven Chen, a geotechnical engineer in the Army Corps of Engineers' Fort Worth District. "Plus it would create debris. And the debris will hit other structures and damage them."