Answer:
The mayor characteristics of these civilizations is that they settle in those places because of the river and to use it in their advantage . However, this use could end in the common flood of the land used, and mostly because these places tend to be plain and without hills, mountains, etc.
Explanation:Floodplain civilization is a concept that describes the action of a society to inhabit a place near a river that is commonly flooded.
The most common reasons to settle in those kind of places can be such as having access to fresh water, the fertility of the land, the cheap transportation using the river and more.
