What method of flood control involves building up the banks a river to keep within its channel?

The method of flood control that involves building up the banks of a river to keep it within its channel is called levées or embankments. These structures are engineered to increase the height of the river's banks and prevent water from overflowing during high flows or floods. Levée systems often consist of earthen embankments, concrete walls, or a combination of both.

Building levées has been a common flood control strategy for centuries, particularly in low-lying areas and floodplains where rivers are prone to overflowing. They aim to contain the river's water within its designated channel, preventing it from spreading and causing flooding in the surrounding areas.

While levées can provide effective flood protection, they also require regular maintenance and reinforcement to ensure their integrity and stability. There can also be environmental concerns associated with levées, as they can alter the natural flow of the river, disrupt ecosystems, and impact habitats.