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Stepped spillway
Recent advances have permitted the construction of large dams, reservoirs and channels. These have necessitated the development of new spillway designs. A key feature of a spillway system is the safe dissipation of a major component of the kinetic energy of the water to avoid damage and failure. It can be achieved by a high-velocity water jet taking off from a ski jump and impinging into a downstream pool of a standard stilling basin, downstream of the chute where a hydraulic jump dissipates the flow energy, or the construction of steps on the spillway chute to assist in energy dissipation: i.e., the stepped spillway. On a stepped chute, the steps drastically increase the rate of kinetic energy dissipation taking place in the spillway, thus eliminating or greatly reducing the need for an energy dissipator at the end of the spillway downstream.
Although the stepped spillway design was common up to the beginning of the 20th century, a lot of expertise has been lost since, and the present expertise is limited to very-simple geometries, namely some flat horizontal stepped prismatic chutes, despite some recent interest in stepped spillway design.
==Historical developments==
The stepped spillway, consisting of wires and channels have been used for over 3,500 years since the first structures were built in Greece and Crete. During the Antiquity, the stepped chute design was used for dam spillways, storm waterways, and in the town water supply channels. Most of these early structures were built around the Mediterranean sea, and the expertise on stepped spillway design was spread successively by the Romans, Muslims and Spaniards.
Although the early stepped spillways were built in cut-stone masonry, unlined rock and timber, a wider range of construction materials was introduced during the mid-19th century, including the first concrete stepped spillway of the Gold Creek dam (1890) in Australia. During the first half of the 20th century, the stepped cascade design became out of fashion, partly because of the maintenance costs but also because of the development in hydraulic jump stilling basins. Yet the long-lasting operation of several famous stepped cascades has demonstrated the soundness of the stepped spillway design.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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