A great basin is a watershed that doesn't flow into the ocean. Parts Of A River By:Maya Miller Period:4 This is the Mississippi Rivers flood plain. The land got a lot spring floods. A watershed is an area of high water going to low then to a large body of water Source of the river severn A body of water that empties into a larger body of water is called a mouth This a smaller stream that that flows into a mainstream, which is a Tributary. The Estuary is when fresh water meets the salt water. Headwaters have very little sun and plants as shown above. Divides are mountain or valley ranges that separate watersheds. A downriver is between the headwaters and floodplain. A confluence is a place where two rivers meet.