By Alastair Leithead
BBC News, Miami
Failures in the flood defence system protecting the US city of New Orleans could have been prevented by relatively cheap modifications, a report says.
Human failures contributed to the devastation, the study says
The American Society of Civil Engineers found that rather than a few breaches in the levees caused by Hurricane Katrina, there were dozens of failings.
The society put some of the failings down to poor construction.
It presented its interim report on the flooding to Congress on Wednesday, six weeks after the hurricane hit.
Hurricane Katrina was a catastrophic storm, but it was the breaches of the levee flood defence system which did the majority of the damage in New Orleans.
The society found that rather than there being a few breaks in the levees caused by water going over the top, there were dozens of breaches across the entire system - much of it flowing through the defences.
The report to Congress stated that if just "relatively inexpensive modifications" had been made "some of the failures would likely have been prevented".
There was criticism that the defences did not cope well, and the report suggests inappropriate materials like sandy soils may have been used.
The society also linked the different authorities maintaining sections of the levees at varying standards, to weakening of defences.
In conclusion Congress was advised to give population centres more protection - and to seriously consider preparing for bigger floods that happen once every 500 years - rather than once every century.