Section 4: Soil and Water Conservation Engineering
Fluid Mechanics
Subtopic: Flow through orifices, weirs and notches
Question Statement:
A triangular V-notch weir is preferred over a rectangular suppressed weir for measuring small irrigation discharges because:
Options:
(A) The head $H$ is significantly larger for a given small discharge, minimizing percentage measurement error ($Q \propto H^{5/2}$ vs $H^{3/2}$)
(B) It requires zero head to discharge water
(C) The discharge coefficient is always equal to 1.0
(D) It prevents silt deposition entirely
Answer Key:
A
Step-by-Step Solution & Explanation
Because $Q \propto H^{2.5}$, small flow rates produce measurable heads over V-notches, whereas rectangular weirs yield tiny heads that are prone to large capillary and reading errors.