Contents preface (VII) introduction 1—37

17.5.2. Bucket-Type Energy Dissipators
When the tail-water depth is either too small or too large for the formation of hydraulic jump, the high amount of energy at the toe of spillway can be dissipated by the use of bucket-type energy dissipators. These can be either: (i) a trajectory (or deflector) bucket, or (ii) a roller (or submerged) bucket energy dissipator.
(i) Trajectory (or Deflector) Bucket: When the tail-water depth is lesser than the depth required for the jump formation and the bed of the river channel is composed of sound rock capable of withstanding the impact of the trajectory jet, a trajectory bucket (also known as a flip or ski-jump bucket) (Fig. 17.23) is generally used as an energy dissipator. The incoming jet of water leaves the bucket as a free-discharging upturned jet and falls into the stream channel some distance downstream of the end of the spillway. The upturned jet gets split into a number of bubbles or smaller jets. The energy is dissipated on account of the increased air resistance (because of splitting of the jet) as well as the impact against water and the channel bed down-stream.
With the end of the lip as the origin of the coordinate system, the path of the trajectory is given by the equation (10):

y =	x tan θ −	x2		(17.25)
4k E cos^2	θ
			1

where, θ, known as the lip angle, is the angle between the curve of the bucket at the lip and the horizontal, E the specific energy, and k₁ is assigned a value of 0.85 to compensate for loss of

594 IRRIGATION AND WATER RESOURCES ENGINEERING
energy and velocity reduction due to the effect of the air resistance, internal turbulence, and disintegration of the jet.
Reservoir water surface

y
	x	Tail
		water
Bucket