Here's why:

* Broad and flat: Floodplains are characterized by their wide, relatively flat surfaces. This is because they are formed by the deposition of sediment carried by rivers as they overflow their banks during floods.

* Carved by wandering streams: Rivers, especially those in their lower courses, often meander across the landscape. As they meander, they erode the surrounding land, creating the wide, flat valley floors.

Let me know if you'd like more information about floodplains!