An Interstate Water System would PREVENT most catastrophic flooding in the USA while supplying water to drought areas. Although it is massive in scale, it would be relatively inexpensive.
Let's install large pumping stations in flood-prone areas (mostly in the eastern and central parts of the nation) and connect them to a network of pipelines and reservoirs which could distribute water to areas in need (mostly the Southwest) for irrigation and firefighting. Rights of way are mostly already in place along the Interstate Highway System and other roadways. The pipelines would carry massive amounts of water away from flood areas BEFORE the water has a chance to rise and cause damage.
Cities and farms in drier areas would benefit from additional water supplies. Everyone WINS.