Never trust a person who says that complex issues have simple solutions.
https://www.cnn.com/interactive/2020/politics/hamburg-iowa-flood-2020-election/
Before the levees, the entire floodplain along 1000 miles of river would be inundated periodically with very slow moving water (due to being spread over thousands of square miles of land). Slow moving water can only carry very fine and light sediments - heavier particles drop out as the velocity decreases. Because of the levees, the river has been restricted to a very narrow channel, which means the velocity, and thus its ability to carry heavier sediments, caused it to be transporting sand instead of just silt. So when the river got out of the artificial channel and slowed down, spreading over the bottomland, it deposited sand.
Land ruined. Town very over.