Question

How is the average velocity along the vertical in a wide stream obtained?

• A. By averaging the velocities at 0.2 and 0.8 depth from surface.
• B. By measuring velocity at 0.6 depth below the surface.
• C. By measuring velocity at half the depth.
• D. By measuring velocity at 0.1 times the depth below the surface.

Answer 1

The correct option is B By measuring velocity at 0.6 depth below the surface.

The velocity profile shows how the average velocity is usually at 0.6 times the total depth from the water surface, or 0.4 times the total depth from the bottom of the channel. This is why, in shallow channels (< 2.5 ft or < 0.75 m), current meter measurements are made at four tenths of the total depth (from the bottom).