Which notch gives the accurate result in measuring low discharge?

Explanation:

Weir or notch is a physical structure of masonry constructed across the channel width to calculate the discharge of the channel section.

Rectangular Notch:

The discharge through a rectangular notch weir is,

\(Q = \frac{2}{3}{C_d}L\;\sqrt {2g} \;{H^{3/2}}\)

Where, Q = discharge of fluid, Cd = Coefficient of discharge, and H = height of water above the notch

Triangular Notch:

A V-notch weir is also called the triangular notch or weir. The discharge over a triangular weir or notch is given by the:

\(Q = \frac{8}{{15}}{C_d}tan\frac{\theta }{2}\;\sqrt {2g} \;{H^{5/2}}\)

Where, Q = discharge of fluid, Cd = Coefficient of discharge, θ = Notch angle, and H = height of water above the notch

A triangular notch or weir is preferred to a rectangular weir or notch due to the following reasons:

• The expression for discharge for a right-angled V-notch or weir is very simple.
• For measuring the low discharge, a triangular notch gives more accurate results than a rectangular.
• In the case of the triangular notch, only one reading i.e H is required for the computation of discharge.