Question

What is the assumption that is taken during the entire design of an overflow spillway?

(a) The upper and lower nappe is subjected to negative pressures

(b) The upper and lower nappe is subjected to full atmospheric pressure

(c) The upper and lower nappe is subjected to zero atmospheric pressure

(d) The upper and lower nappe is subjected to both positive and negative pressure

The question was asked in quiz.

This key question is from Ogee Profile topic in section Spillways, Energy Dissipators and Spillway Gates of Irrigation Engineering

Answer 1

The correct answer is (b) The upper and lower nappe is subjected to full atmospheric pressure

For explanation I would say: In actual practice, the development of negative pressure due to insufficient aeration takes place beneath the nappe due to the removal of air by the falling jet. But the entire design has been done with the assumption that the upper and lower nappe is subjected to full atmospheric pressure.