But another mass movement was taking place on the other sides of the highways.
Thousands of men from Mexico and Central America were driving into the city. Word had spread throughout the Latino immigrant diaspora in America that the city had plenty of work, construction wages had doubled to $16 an hour and no one was asking for papers.
"It was like a Gold Rush," said Oscar Calanche, a Guatemalan immigrant who lived in New Orleans before the storm and returned as soon as the waters receded. "In one car there'd be three up front and three or four in the back, with suitcases and tools on top. It looked like a river of people from our countries."
Latino workers have gutted, roofed and painted houses and hauled away garbage, debris and downed trees. Undocumented workers have installed trailers to house returning evacuees at New Orleans City Park, their pay coming from FEMA subcontractors.
"It's all illegals doing this work," said Rey Mendez, a FEMA trailer subcontractor from Honduras.
No one knows how many Latino immigrants are here, but John Logan, a Brown University demographer who has studied the city since Katrina, says "there must be 10,000 to 20,000 immigrant workers in the region by now, and the number is going to grow."
As the Senate debates new immigration laws and marchers demonstrate across the country, these immigrants offer another reminder of the country's reliance on undocumented labor from Latin America.
As New Orleans redefines itself after Katrina, the influx of large numbers of Latino immigrants is another jolt for a city that has historically thought of itself as black and white.
A port town owned at times by three different countries, New Orleans once absorbed immigrants.
While the South's feeble economy, racism and xenophobia kept out new people and influences, New Orleans took in waves of newcomers — Italians, Greeks, Germans and Irish — in the decades before World War I. Later arrivals came from Honduras, Cuba and Vietnam.
But beginning in the 1970s, the port downsized, businesses left town, wages fell, welfare rolls and crime rose as the public education system collapsed. A black underclass took low-skilled, low-wage jobs. Fewer immigrants moved to town.
The rest of the South, meanwhile, became what New Orleans had been: Atlanta, Memphis, Nashville and Charlotte saw tens of thousands of Mexicans arrive, taking jobs in hotels, restaurants, construction and landscaping. Mexicans slaughtered pigs in Guymon, Okla., and made carpeting in Dalton, Ga. Historians call their arrival the largest influx of foreign workers to the South since the days of slavery.
But New Orleans' listless economy was hardly a magnet for such workers.
According to the 2004 U.S. Census, New Orleans had 1,900 Mexicans. Nashville had 80,000 Mexican immigrants by 2000, city officials there estimated.
Before Katrina, the Latinos in New Orleans, mostly middle class, made up about 3% of the population.
"We were the first melting pot city in America," said Lawrence Powell, a Tulane University historian. "It's striking that those great waves of immigration from Mexico passed us by."
But that changed in September.
Leonel Santos was working in Virginia when a New Orleans roofing contractor he knew from his hometown of San Francisco del Mezquital, in Mexico's Durango state, called. The contractor sent a car that picked up Santos and seven other workers in Virginia and North Carolina and brought them to New Orleans.