A timeline of information regarding Katrina is available here: Katrina Timeline Info Dump. Also see Bush's Disastrous Response: A Timeline. The folks at ThinkProgress are compiling a most complete source of information spanning the period from August 26 through September 3. And perhaps the best resource of this nature is being developed by the Daily Kos's dKosopedia here: Hurricane Katrina Timeline, augmented by a Katrina commentary page and a Katrina issues page.
If you still need convincing of the enormity of the New Orleans flooding, visit the before-and-after gallery of satellite images at Global Security.