Question

Sharper crest of an ogee spillway 
1. Increases the value of coefficient of discharge
2. Decreases the effective head
3. Increases stability of crest due of hydrostatic pressure
4. Has no effect on any one of the above

Answer 1

Correct Answer - Option 1 : Increases the value of coefficient of discharge

Concept:

Ogee (Overflow) Spillway:

• This type comprises a control weir, which is ogee or 'S' shaped.
• The ogee shape conforms closely to the profile of aerated lower nappe and falling from a sharp-crested weir.
• The upper curve at the crest may be made either broader or sharper than the nappe.
• A broader curve will support the sheet and hydrostatic pressures will occur along the contact surface.
• The support sheet thus creates a backwater effect and reduces the coefficient of discharge.
• The sharper crest on the other hand creates negative pressure, increases the effective head, and thereby discharge.
• This type of spillway should be constructed in the Nalla itself as far as possible