They can declare it .. but can't enforce it??
Contrary to many media reports, martial law has not been declared in New Orleans in the aftermath of Hurricane Katrina, because no such term exists in Louisiana state law[4]. Rather, a state of emergency has been declared, which does give some powers similar to that of martial law. On the evening of August 31, New Orleans Mayor Ray Nagin did declare "martial law" (in name at least) in the city and said that "officers don't have to worry about civil rights and Miranda rights in stopping the looters." [5]
I don't know, but they better get a handle on this fast. People are telling me they will not bring supplies now and not all the evacuees are criminals, so the good will suffer because of the bad.