I think large and medium scale shelters to aid refugees are a far more likely scenario than "detention camps" to contain them. The first few days are likely to be chaotic, and crime rates may tick up, but large scale violence and rioting are unlikely.

In my extensive experience with displaced persons, I've found them to be very cooperative and reasonably orderly, on the whole, and I've seen the ability law enforcement has to exercise it's surge capacity in disasters (court officers, probation officers, fish & game officers, reserve deputies, DMV officers, campus police, marine patrol, state troopers, National Guard, Federal Protective Service, FBI, Border Patrol, airport police, etc.)