Grand Forks ND/E. Grand Forks MN population about 50,000 flooded in 1997. There was no looting, no one fired on those trying to help, no arson, no deaths.
I lived through that, and have many stories to tell. Oh yes, there where gangs of people roaming around, just looking for something to do to help.
We saved my brother's house by intensively sandbagging using an army of volunteers that just showed up.
I pulled "pump watch" in the middle of the night and heard on the radio at 3 AM that volunteers were urgently needed in a certain area of town. I had just moved from a major urban area so I thought "no way". An hour later they put out the call for no more as they had too many people there.
The National Guard showed up to provide security, but usually carried no weapons during the day.