GUO Xin-lei, YANG Kai-lin, XIA Qing-fu, FU hui

State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China

Abstract: The concept of Piano Key Weir (PKW) is a new technique and trend used to rehabilitate numerous existing dams, which can increase the unit discharge at the unregulated spillway inlet for similar heads and widths. As it is a relatively novel structure, its hydraulic design remains problematic. The discharge capacity character is one of the most important hydraulic features which directly linked to the maximum reservoir level during floods under PMF. The recently published equations relating to the head discharge ratio of PKW was summarized. Combining with the existing experimental data, the paper proposed a new formula based on the dimensional analysis and multi-parameter optimization, then the discharge capacity and increase ratio of PKW was studied. The results show that the efficiency of PKW is particularly high for the small head ratio of H / P, for H/P <0.2, the increase ratio is bigger than 3 and then the total length plays the leading role when H/P increased. The practical extend of increase ratio is between 1.2 and 3.5. Also the predicted values agree well with the published experimental results with the average error less than 8%, which is smaller than the Machiels equation. The proposed head discharge relationship can be used for the design of PKW and helps to provide a reference.

Key words: Piano Key Weir; discharge capacity; spillway; flood standard; upgrade and rehabilitate

Published in: Journal of Hydraulic Engineering, Vol. 45, No. 7, 2014