Many towns in flood-prone areas are surrounded by___ that are built to hold back rising water.

Flood barriers

Explanation:

Many towns in flood-prone areas are surrounded by flood barriers that are built to hold back rising water during seasonal highs.

Flood barriers are water resistant walls that are used to prevent breaking water during a high period of inundation from their channels. They are usually vertical artificial structures which can be temporary or permanent. They help to hold or contain the flood water during the high season. These walls prevents flood plains and other nearby areas from getting flooded during the rainy season.