I do not think that the United States government is obligated to refund the rebuilding of New Orleans after the natural disaster Hurricane Katrina destroyed much of the city. I do not think that the government is required to rebuild cities after natural disasters occur, that is what insurance is for.
No, the U.S. government is not obligated to refund and rebuild New Orleans. It is not the United States' job to insure every person, municipality, or state that suffers a natural disaster. Instead, the person or government should have their own insurance. The United States should allow market forces to settle what parts of New Orleans are rebuilt.