In conclusion I have realized that levees are the best way to reduce flood damage. Levees may solve the problem temporarily, but during the next flood rivers would flood even more unless workmen dredge mud from the bottom of the river. Sandbags help, but have the same problems that levees do. Dams make the flood worse, but in an area that would not harm as much as in an urban area. Canals help, but do not eliminate damage completely.
Levees are the best way, but they take time to build, and require man power to dredge the mud.