Question

It is believed that the design of appurtenances in the stilling basin can reduce the basin length by 70- 80%. Give comments on this statement.

Answer 1

Water moving through the spillway of a dam contains a large amount of energy. This energy can cause erosion at the outlet which can lead to instability of the spillway. Failure to properly design, install, or maintain a stilling basin could lead to problems such as undermining of the spillway and erosion of the outlet channel and/or embankment material. These problems can lead to failure of the spillway and ultimately the dam.

A stilling basin provides a means to absorb or dissipate the energy from the spillway discharge and protects the spillway area from erosion and undermining.

In the absence of stilling basin an outlet erosion control structure such as a headwall/endwall, impact basin, Type II or Type III basin, baffled chute, or plunge pool has to be provided for the purpose of an energy dissipating device.

In a stilling basin kinetic energy causes turbulences and it is ultimately lost as heat and sound energy. So the presence of stilling basin eliminate the requirements of any extra energy dissipation structure formation and reduce almost 70-80% basin length.

Experiments have conducted to characterize forced hydraulic jumps in stilling basins for enforced cases due to tail water level. The case with a single tall sill simulated in a horizontal flume downstream of a sluice gate. Results of experiments confirm significant effect of tall sill on dissipation of energy in shorter distance.