Question

If the operating head on an ogee spillway is more than the design head then ________________

(a) the pressure on the crest will be zero

(b) the pressure on the crest will be negative causing cavitation

(c) the pressure on the crest will be positive

(d) the discharge coefficient of the spillway will be reduced

The question was asked in homework.

I'm obligated to ask this question of Ogee Spillway in division Spillways, Energy Dissipators and Spillway Gates of Irrigation Engineering

Answer 1

Right choice is (b) the pressure on the crest will be negative causing cavitation

To elaborate: The lower nappe of the falling jet may leave the ogee profile when the operating head of the spillway is more than the design head. This generates negative pressure at the point of separation which leads to the formation of cavities in the water resulting in cavitation.