Question

At the foot of a spillway, the jump rating curve is below the tail water curve at low flows and above it at high flows. The suitable type of energy dissipater for this situation is:-
1. A sky-jump bucket
2. A horizontal apron
3. A sloping apron
4. A stilling pool

Answer 1

Correct Answer - Option 4 : A stilling pool

Definition of stilling basin: 

A depression in a channel or reservoir deep enough to reduce the velocity or turbulence of the flow.

IS code for stilling basin (IS 4997): Criteria for design of hydraulic jump type stilling basins with horizontal and sloping aprons.

How does the energy dissipation occur in stilling basin:

Aprons concrete impact basin is an energy-dissipating device located at the outlet of the spillway in which flow from the discharge conduit strikes a vertical hanging baffle. Energy dissipation occurs as the discharge strikes the baffle, thus, performance is not dependent on the tailwater.

• Stilling basin energy dissipator with pool - MLL Concrete
• Stilling basin energy dissipator with pooapronsl