A triangular notch is preferred over a rectangular notch because:

Explanation:

Advantages of a triangular notch over a rectangular notch:

A triangular notch claims the following advantages over a rectangular notch;

• For a right-angled V-notch or weir, the expression for the computation of discharge is very simple.
• For low discharges, a triangular notch gives more accurate results than a rectangular notch.
• In a given triangular notch, only one reading i.e., head (H) is required to be taken for the measurement of discharge.
• Its crest length is zero.
• Ventilation of a triangular notch is not necessary.
• The same triangular notch can measure a wide range of flows accurately.

​Hence option (4) is the correct answer.