Question

If the head of the water over the spillway is less 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 discharge coefficient of the spillway is increased

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

I had been asked this question in examination.

The question is from Ogee Spillway topic in chapter Spillways, Energy Dissipators and Spillway Gates of Irrigation Engineering

Answer 1

Correct option is (d) the discharge coefficient of the spillway will be reduced

Best explanation: If the head of water over the spillway is less than the design head, the falling jet would adhere to the crest of the ogee spillway. This causes positive hydrostatic pressure and thereby reduces the discharge coefficient of the weir.