Posse Comitatus doesn't really apply they're not enforcing a law or acting as a policing force which is all that law actually cares about. The Army Corps of Eng

Posse Comitatus doesn't really apply they're not enforcing a law or acting as a policing force which is all that law actually cares about. The Army Corps of Engineers does a lot of projects like this, it's part of the reason they exist at all. Lots of the flood control along the Mississippi for example are COE works and they come in during emergencies to do stuff like this. For example during Katrina they were the ones repairing the dykes that had failed around New Orleans.