The former head of the US emergency agency has acknowledged that the government knew the flood barriers protecting New Orleans were inadequate.
By Matthew Davis
BBC News, Washington
Michael Brown was forced to quit the Federal Emergency Management Agency (Fema) after bitter criticism of the response to Hurricane Katrina.
In a BBC documentary, he admitted that the levees had not been upgraded to deal with the most powerful hurricanes.
The programme, The Hurricane That Shook America, will be shown on Wednesday.
In the interview, Mr Brown said that Fema had positioned resources at the New Orleans Superdome stadium to help people who were sheltering there.
But he said he was amazed when more and more people kept coming in - a result he described as an "fascinating phenomena".
The documentary also reveals that a key briefing officer within Fema sent a message directly to Mr Brown early on the day before Katrina hit, warning him of potentially disastrous flooding in New Orleans, which could trap more than 100,000 people.
In the event, Katrina devastated parts of Louisiana and Mississippi on 29 August, causing massive flooding in New Orleans, killing about 1,200 people and causing misery to those unable to escape to safety.
Last month, Mr Brown testified to a congressional panel investigating shortcomings in the rescue effort, defending his role and saying that Louisiana officials had been reluctant to order evacuations.
He said his "biggest mistake" had been not recognising that Louisiana was "dysfunctional".
A year before Katrina, emergency teams from the area sat down with hurricane experts and other officials - including senior members of Fema, to run a disaster simulation called Hurricane Pam - which had selected New Orleans as the target.
They calculated the impact of 120mph winds on the city and simulated a massive storm surge which would break over the levees with potentially disastrous consequences for the city.
Ivor van Heerden, an expert on hurricanes from Louisiana State University, told the BBC that local officials had taken the predictions of the Pam exercise rather more seriously than their federal counterparts.
Three days after Katrina hit, President Bush appeared on national television to offer a possible explanation for the unfolding disaster, which was battering his own reputation.
"There is frustration, but I want people to know that there is a lot of help coming..." the president said.
"But these levees got breached and people were expecting a storm, but I don't think anyone anticipated a breach of the levees."
But Mr Brown says the problems were well-known.
"We understood exactly what was going on with the levees," he told the BBC. "And we knew that the levees were dangerous."
While the federal government is responsible for funding and building the levees, successive administrations have failed to address the challenge of building levees to withstand a category four or five storm like Katrina.
New Orleans was devastated by the impact of Hurricane Katrina
But one of the most keenly felt criticisms of the response to Katrina is the charge that Fema failed to make good on its promises of immediate aid.
Walter Maestri, head of emergency preparedness for Jefferson Parish, told the BBC that Fema officials promised emergency teams from the area that they would supply food, water, medical provisions, and assistance with transporting evacuees from the city - all within 48 hours of the emergency.
In the event, these emergency teams were left without the help they asked for.
Mr Brown now concedes that despite years of planning, the emergency response was not ready.
"The planning was put together... we did that exercise and had the conclusions in July last year, and then through our budget cycles have to decide what resources to apply to it, so we'd just started that process.
"It's nobody's fault that the hurricane hit when it did."
The Hurricane That Shook America was broadcast on Wednesday, 12 October, 2005 at 2100 BST on BBC Two.