Parts of a River
A watershed is basically a system that gets water and then water comes down into a bigger body of water as you see in this diagram.
A source is a place where water comes from and as you see in the picture the source is that hole where water is coming from.
The mouth/delta is the bottom of the watershed that forms from the deposition sediments.
A great basin is a watershed where the water doesn't flow into a ocean. For example the great salt lake is a great basin.
A divide is a mountain or valley range that separates watersheds. As you see in the picture the mountains are representing the divide.
In this video there is a heads water flowing. A heads water is a stream with not lots of sunlight or plant life.
A flood plain is the reality flat land to a river channel that is underwater when the river floods.
A downriver is a area that is between head water and floodplain.
Small stream that leads into a main stream.