A chute is the means by which water is transferred over the crest to the river bed below the dam. Its function is to prevent damage to the valley walls that could endanger the dam. It may or may not serve to dissipate some of the energy in the water.

Cascade spillways - used to dissipate energy
The rock must be massive and free from close jointing and competent. The rock excavated must be used in the dam if the scheme is to be economically viable.

Lined Chutes - at most sites a concrete lined chute is required. The chute width is determined by the length and arrangement of the spillway crest, the total energy in the water and the economical relation between the width (including excavation costs) and the height of the side walls of the chute. The height of the chute wall is also important because the water could erode the side slopes.

At the bottom of the chute the water may enter a dissipator basin, or be directed around a flip bucket so that much of its energy is dissipated in air. Vibration will cause movement of the slabs and even failure of them. It is essential that slabs are anchored to the rock with steel rods. The figure shows the correct way of laying slabs so they do not lift up.

(C) Thomas, Henry H. The Engineering of Large Dams