I was referring to a New Orleans flood in the 1970's. When our Disaster Action Team got there, there were no local Red Cross personnel, either paid or volunteers, to be found. We had to jumpstart the relief efforts blind, and try to recruit volunteers. Four days after the flood we were still finding large areas of the city that nobody even knew were flooded (except the people living there of course).
One of the first things the Red Cross does in a disaster is called a "windshield survey" to identify the areas affected and estimate how many homes are damaged. Because there is no incentive for the Red Cross to fudge the numbers, their damage estimates are the official ones used by the government and the press. If the windshield survey isn't done immediately, or is inaccurate, it screws up the whole relief effort because the government relies on those estimates to know where and how much assistance is needed.
I wasn't involved in the Katrina effort, so I can only assume that after Katrina, the local chapter dropped the ball AGAIN.