http://www.nola.com/hurricane/index.ssf?/washingaway/thebigone_1.html
"...Joseph Suhayda, a Louisiana State University engineer who is studying ways to limit hurricane damage in the New Orleans area..."
(Below he discusses what would happen if a Cat 5 hit. Elsewhere he said that this scenario is possible if the center of a Cat 5 hit within a 30 mile radius of New Orleans, and could also happen with a Cat 4 or slow-moving Cat 3 striking in a smaller radius.)
..."The worst case is a hurricane moving in from due south of the city," said Suhayda, who has developed a computer simulation of the flooding from such a storm. On that track, winds on the outer edges of a huge storm system would be pushing water in Breton Sound and west of the Chandeleur Islands into the St. Bernard marshes and then Lake Pontchartrain for two days before landfall.
"Water is literally pumped into Lake Pontchartrain," Suhayda said. "It will try to flow through any gaps, and that means the Inner Harbor Navigation Canal (which is connected to Breton Sound by the Mississippi River-Gulf Outlet) and the Chef Menteur and the Rigolets passes.
"So now the lake is 5 to 8 feet higher than normal, and we're talking about a lake that's only 15 or 20 feet deep, so you're adding a third to a half as much water to the lake," Suhayda said. As the eye of the hurricane moves north, next to New Orleans but just to the east, the winds over the lake switch around to come from the north.
"As the eye impacts the Mississippi coastline, the winds are now blowing south across the lake, maybe at 50, 80, 100 mph, and all that water starts to move south," he said. "It's moving like a big army advancing toward the lake's hurricane-protection system. And then the winds themselves are generating waves, 5 to 10 feet high, on top of all that water. They'll be breaking and crashing along the sea wall."
Soon waves will start breaking over the levee.
"All of a sudden you'll start seeing flowing water. It'll look like a weir, water just pouring over the top," Suhayda said. The water will flood the lakefront, filling up low-lying areas first, and continue its march south toward the river. There would be no stopping or slowing it; pumping systems would be overwhelmed and submerged in a matter of hours.
"Another scenario is that some part of the levee would fail," Suhayda said. "It's not something that's expected. But erosion occurs, and as levees broke, the break will get wider and wider. The water will flow through the city and stop only when it reaches the next higher thing. The most continuous barrier is the south levee, along the river. That's 25 feet high, so you'll see the water pile up on the river levee."
As the floodwaters invade and submerge neighborhoods, the wind will be blowing at speeds of at least 155 mph, accompanied by shorter gusts of as much as 200 mph, meteorologists say, enough to overturn cars, uproot trees and toss people around like dollhouse toys.
The wind will blow out windows and explode many homes, even those built to the existing 110-mph building-code standards. People seeking refuge from the floodwaters in high-rise buildings won't be very safe, recent research indicates, because wind speed in a hurricane gets greater with height. If the winds are 155 mph at ground level, scientists say, they may be 50 mph stronger 100 feet above street level.
Buildings also will have to withstand pummeling by debris picked up by water surging from the lakefront toward downtown, with larger pieces acting like battering rams.
Ninety percent of the structures in the city are likely to be destroyed by the combination of water and wind accompanying a Category 5 storm, said Robert Eichorn, former director of the New Orleans Office of Emergency Preparedness. The LSU Hurricane Center surveyed numerous large public buildings in Jefferson Parish in hopes of identifying those that might withstand such catastrophic winds. They found none.
Amid this maelstrom, the estimated 200,000 or more people left behind in an evacuation will be struggling to survive. Some will be housed at the Superdome, the designated shelter in New Orleans for people too sick or infirm to leave the city. Others will end up in last-minute emergency refuges that will offer minimal safety. But many will simply be on their own, in homes or looking for high ground.
Thousands will drown while trapped in homes or cars by rising water. Others will be washed away or crushed by debris. Survivors will end up trapped on roofs, in buildings or on high ground surrounded by water, with no means of escape and little food or fresh water, perhaps for several days.
"If you look at the World Trade Center collapsing, it'll be like that, but add water," Eichorn said. "There will be debris flying around, and you're going to be in the water with snakes, rodents, nutria and fish from the lake. It's not going to be nice."
Mobilized by FEMA, search and rescue teams from across the nation will converge on the city. Volunteer teams of doctors, nurses and emergency medical technicians that were pre-positioned in Monroe or Shreveport before the storm will move to the area, said Henry Delgado, regional emergency coordinator for the U.S. Public Health Service.
But just getting into the city will be a problem for rescuers. Approaches by road may be washed out.
"Whether or not the Airline Highway bridge across the Bonnet Carre Spillway survives, we don't know," said Jay Combe, a coastal hydraulic engineer with the corps. "The I-10 bridge (west of Kenner) is designed to withstand a surge from a Category 3 storm, but it may be that water gets under the spans, and we don't know if it will survive." Other bridges over waterways and canals throughout the city may also be washed away or made unsafe, he said. In a place where cars may be useless, small boats and helicopters will be used to move survivors to central pickup areas, where they can be moved out of the city. Teams of disaster mortuary volunteers, meanwhile, will start collecting bodies. Other teams will bring in temporary equipment and goods, including sanitation facilities, water, ice and generators. Food, water and medical supplies will be airdropped to some areas and delivered to others.
Stranded survivors will have a dangerous wait even after the storm passes. Emergency officials worry that energized electrical wires could pose a threat of electrocution and that the floodwater could become contaminated with sewage and with toxic chemicals from industrial plants and backyard sheds. Gasoline, diesel fuel and oil leaking from underground storage tanks at service stations may also become a problem, corps officials say.
A variety of creatures -- rats, mice and nutria, poisonous snakes and alligators, fire ants, mosquitoes and abandoned cats and dogs -- will be searching for the same dry accommodations that people are using.
Contaminated food or water used for bathing, drinking and cooking could cause illnesses including salmonella, botulism, typhoid and hepatitis. Outbreaks of mosquito-borne dengue fever and encephalitis are likely, said Dr. James Diaz, director of the department of public health and preventive medicine at LSU School of Medicine in New Orleans.
"History will repeat itself," Diaz said. "My office overlooks one of the St. Louis cemeteries, where there are many graves of victims of yellow fever. Standing water in the subtropics is the breeding ground for mosquitoes."
What a terrible scenario. I pray to God that this will never happen. It would be as bad as the Christmas tsunami last year.
I really hope that I'm overreacting to what I see this afternoon. I probably am, because I can't imagine it being worse than I suspect it's going to be.
Maybe Katrina will slide off to the east or west and inflict hell on a smaller community. Maybe she'll suddenly lose intensity before landfall. Those things frequently happen with hurricanes.
But if she hits NO as a Cat 4 storm, we'll be talking about it for the rest of our lives. We're still talking about the Galveston hurricane more than 100 years later.