Which of the following is FALSE regarding triangular weir?

Answer:

Statement 4: False Ventilation of triangular weir is not necessary.

Weir:

A weir is a concrete or masonary structure, placed in an open channel over which the flow occurs. It is generally in the form of vertical wall, with a sharp edge at the top, running all the way across the open channel. The notch is of small size while the weir is of a bigger size. The notch is generally made of metallic plate while weir is made of concrete or masonary structure.

Triangular weir:

The expression for the discharge over a triangular weir or notch is

Q = \(\frac{8}{{15}} \times {C_d} \times tan\frac{θ }{2} \times \sqrt {2g} \times {H^{\frac{5}{2}}}\)

From this expression flow through the weir depend upon the vertex angle (θ) and coefficient of discharge (C_d) is constant for all the heads, the value of C_d is nearly equal to 0.6.

Rectangular weir:

The expression for the discharge over a rectangular weir or notch is

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

Advantage of triangular weir over rectangular weir:

A triangular weir is preferred to a rectangular weir due to following reason.

(1) The expression for discharge for a right angled V- notch or weir is very simple.

(2) For measuring low discharge, a triangular weir gives more accurate results than a rectangular weir.

(3) In case of triangular weir, only one reading, (H) is required for the computation of discharge.

(4) Ventilation of triangular weir is not necessary.