Ski Jump and the Main Component of It

Ski jump was introduced in 1930s in France. Energy dissipation downstream of large dams is a serious concern. Trajectory spillways or Ski jumps are employed whenever the velocity at the dam foot is in excess of typically 20m/s because of problems with stilling basins in terms of cavitation, abrasion and uplift. Ski jump are currently widely used because they appeared to be only hydraulic element allowing for the hydraulically safe control of large quantities of hydraulic excess energy during flood season.

In dam engineering Ski jumps are a common hydraulic structures with the function of deflecting high velocity discharge from large dam spillways and chutes to produce a free trajectory. This type of hydraulic structures utilized the effects of air resistance and air entrainment in combination with impact diffusion to dissipate the energy and to reduce the risk of downstream erosion.

A hydraulic structure can be built in rivers, a sea, or any body of water where there is a need for a change in the natural flow of water. A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture and navigation. A spillway is a structure used to provide the controlled release of flows from a dam  into a downstream area. A spillway is located at the top of the reservoir pool. Dams may also have bottom outlets with valves or gates which may be operated to release flood flow, and a few dams lack overflow spillways and rely entirely on bottom outlets. When spillways are at high heads and velocity of the water is high, flip bucket or ski jump buckets are used. This helps to enhance energy dissipation and also to reduce the scouring of riverbed due to impact.

The main component of a Ski jump energy dissipator is the Ski jump bucket or flip bucket which is not an energy dissipator in itself but plays an integral part of energy dissipation process. In general flip buckets are designed and constructed with horizontal cross-sections. The primary purpose of the flip bucket is to deflect high velocity flow up and into the air in the form of a jet trajectory where the location of impact fall at a sufficient distance from the dam toe as to reduce any risk of structural damage.

Ski jump is a major element of each dam spillway because these are the only structures able to accomplish satisfactory energy dissipation for take-off velocities in excess of 20m/s.

Overall, ski jumps are mostly provided at the end of high head spillways or bottom outlets to enhance energy dissipation and also to avoid critical phenomena related to high speed flow. For particular applications they may also include a horizontal deviation take-off lip to deflect the jet or to improve the disintegration process. 

07 July 2022
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