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THE PIANO KEYS WEIR: A NEW COST-EFFECTIVE SOLUTION FOR SPILLWAYS

Dòng chảy tràn tự do là đơn giản và an toàn hơn so với những người thân gated, nhưng cụ thể lưu lượng thấp hình dạng truyền thống của họ đòi hỏi phải có độ sâu thợ chải tuyết nỉ cao đổ và do đó khoản lỗ khổng lồ dung lượng lưu trữ (100 x 109m3 trên toàn thế giới). Hình dạng mới của dòng chảy tràn tự do ("phím Piano đập") có thể làm tăng dòng chảy cụ thể gấp bốn lần hoặc nhiều hơn. Nó có thể làm giảm đáng kể chi phí nhất mới đập và tăng lên, với chi phí thấp | www.vncold.vn www.vncold.vn www.vncold.vn www.vncold.vn THE PIANO KEYS WEIR A NEW COST-EFFECTIVE SOLUTION FOR SPILLWAYS F. Lempérière Hydrocoop France A. Ouamane Biskra University Algeria Free-flow spillways are simpler and safer than gated ones but the low specific flow of their traditional shapes requires high spilling nappe depths and thus huge losses of storage 100 x 109m3 worldwide . A new shape of free-flow spillway the Piano Keys weir can increase the specific flow fourfold or more. It could substantially reduce the cost of most new dams and increase at low cost. the safety and the storage and or the flood control efficiency of many existing dams. Most existing free-flow spillways have a standardized shape Creager weir and are placed upon concrete gravity dam structures. Their drawback is their low specific flow which is in m3 s m close to 2.2 h 1.5 h being the nappe depth in metres . Consequently the loss of live storage corresponding to the maximum nappe depth may be 20 to 50 per cent compared with a gated reservoir even if using longer spillways than with gates. It is thus very advantageous to increase the specific flow as much as possible. Some tens of existing spillways have been designed accordingly as vertical walls on a flat bottom with a trapezoidal labyrinth layout which is much longer than the spillway length often four times. They usually double the specific flow of a Creager weir. They require 1 or 2 m3 of reinforced concrete to increase the flow by 1 m3 s and have mainly been used for specific flows in the range of 10 m3 s m. Exceptionally the Ute dam in USA increased the specific flow by 30 m3 s m it required 60 m3 of reinforced concrete per meter. Apart from its cost for high flows the main drawback of the traditional labyrinth solution vertical walls and flat bottom is that it cannot be used on top of the usual concrete gravity dam sections and requires a substantialy flat area. It can therefore only be used for a few dams and in fact has .