What do we call the high land that separates two drainage basins?

The high land that separates two drainage basins is referred to as a watershed. This term describes a geographical feature that acts as a barrier directing the flow of water into different river systems or basins. When precipitation occurs, water on one side of the watershed will flow into one drainage basin, while water on the other side will flow into a different basin.

Understanding the concept of a watershed is crucial in the study of river systems and hydrology, as it plays a significant role in determining how water moves through landscapes, impacting ecosystems, agriculture, and human activities. The other options refer to different geographical features and do not fit the definition of a watershed: for instance, a floodplain is a flat area adjacent to a river that may become flooded during heavy rains; a valley is a low area of land between hills or mountains; and a delta forms at the mouth of a river where it meets a larger body of water and sediment settles.