Question

What do you mean by drainage and river system

Answer 1

drainage means a hole were wastes from all house join together in one hole.

Answer 2

both river basins and water sheds are areas of land  that drain to particular water body, such as a lake, stream,river or estuary. In a river basin, all the water drains to a large river. The term  watershed is used to describe a smaller area of land that drains to a smaller stream, lake or wetland.