I think that the best way to control floods is to use canals.
Canals take excess water, and channels it to another place.
Canals can even be used to irrigate fields, and to help farmers with crops. For emergency flooding sandbags work well because they stop water from leaking through and the bags can be moved quickly and easily. My purpose was to see what the best way to reduce flood damage is. Even though levees worked well, they had a bad side effect. Sandbags did not work well.