That's right!

Water in a stream moves fastest near the surface and slowest near the bottom where the flow is slowed by friction from the roughness of the bed material.

To compute the discharge of a stream, we need to compute velocity, which, as you now know, changes with depth. To make the best estimate of a stream's velocity hydrologists use the average velocity of a stream.

The question is "where is the average velocity measured?" Is it near the middle, or nearer the top, or nearer the bottom?

Click the "Next" button to find out.