Katrina will be the costliest disaster to date.
One of the odd things about flood damage is that almost no further research is spawned from major flood events, unlike earthquakes, wind events, even crashing commercial jets into skyscrapers. I am sure that there will be significant engineering research in the area of levee construction, but the damage to New Orleans is not due to levee failure - the levees simply aren't high enough to contain the storm surge of a Cat-5 hurricane event.
There will be some secondary research regarding the safeguarding an re-initiation of water treatment facilities following flood events, but this work is already going on, and has been since at least the '93 floods in the Missouri and Mississippi valleys.
Oh, and further to my first statement, the next major disaster will be most costly to date whenever it happens. The price of devastation is an inflation-gobbling whore.