If it was all about massive earth moving, you’d think some of the people in a flood zone would build an artificial mesa and then build their house on top of it. Maybe a lot of people do this, but it doesn’t make for amazing photos.
Sometimes I wonder if some of the larger of the mysterious Indian mounds found in the Mississippi valley were simply constructed to keep their important structures above the flood plain. Floods create amazingly fertile land, and it might be worth the investment of time and effort to a sophisticated agriculturual tribe to make flood-proof homes and storage facilities and then just go down and plant when the floods are done.