When a subsidiary channel joins up with a main river along with other channels, these channels are known as Tributaries.
What are tributaries?
These are channels that join up with a river and feed the river water to keep it flowing.
These tributries can come from several sources such as lakes, other rivers, and even rainfall but their purpose is to feed the main river that they are connected to.
Find out more on tributaries at https://brainly.com/question/65521.
