Debris lodged in bottom of a v-notch weir would cause the flow meter reading to read higher, lower, or the same?

• A. Higher
• B. Lower
• C. The same
• D. Uncertain

Answer: (A)

Blockage at the bottom of a V-notch weir raises the water height as the flow is constricted. Since a V-notch’s discharge is calculated from the head—the height of water above the notch—the increased head makes the meter indicate more flow than is actually passing through. Debris reduces the actual passage for a given head, but the higher head it creates makes the discharge reading appear larger when the meter converts head to flow. So the flow meter would read a higher value.