How does the amount of rain affect the volume of water traveling down the river? independent variable? dependant variable? hypothesis?

The volume of water that flows through a river within a given amount of time -- known as the discharge -- also affects its velocity. As the volume of water in a river increases, through smaller streams flowing into it, for example, the velocity of the river increases.

this is more of a statement than a question. is there answers to go along with this, or is it opinion based?