What should be done to dissipate the residual energy, if the tail water deficiency is small? 

Explanation:

When the tail water rating curve is below jump height rating curve at all discharges

• If the tail water depth is very low, the water may shoot out of the above bucket and fall harmlessly into the river at some distance downstream of the bucket. This bucket is then known as Ski jump.

• The second solution to this problem can be the provision of providing a sloping apron but below the river bed. The required depth  which is greater than tail water depth can thus be made available by letting the jump form on this sloping apron as shown.

• The third solution to this problem may be the construction of a subsidiary dam below the main dam, so as to increase the tail water depth and cause a jump to form at the toe of the main dam.

• If the tail water deficiency is small, a baffle wall or a row of friction blocks may be provided so as to dissipate the residual energy.

Additional InformationWhen TWC coinciding with JHC at all discharges

• This is the most ideal condition for jump formation.
• The hydraulic jump will form at the top of the spillway at all discharges. In such a case a simple concrete apron of length 5 (y₂ – y₁) is generally sufficient to provide protection in the region of hydraulic jump.