The amount of water flowing through a channel over a given amount of time is called its:

A) discharge
B) rate of flow
C) velocity
D) drainage basin

Discharge

The volume of water flowing through some stretch of a river or stream per unit of time.

Rate of Flow

The velocity at which a fluid (liquid or gas) moves through a channel, pipe, or porous medium.

Channel

A natural or artificial waterway through which water flows.