Laboratory Study of Discharge Coefficients of One and Two-Cycle Piano Key Weir and Comparison of them with Rectangular Labyrinth Weir

Piano key weirs (PKWs), a new type of weirs with a very high discharge capacity, can be used as high performance economic structures. This type of weirs is a good alternative to linear weirs, because they increase the discharge per unit width at the span of non-regulated weirs for the same water load and weir width. In this study, the discharge coefficient of piano key weirs was compared with that of a rectangular labyrinth weir. The results showed 38% increase in the discharge coefficient of the piano key weirs as compared to that of the rectangular labyrinth weir. The difference between the discharge coefficients of the weirs was reduced by increasing hydraulic load when reaching the submergence discharge. The difference was reduced about 24% at high discharges. In addition, the tailwater level was gradually increased from the weir crown level.