Abstract
The main objective of this investigation is to obtain performance efficiency and the coefficient of discharge for Piano Key weir with downstream overhang. One hundred thirty five experimentswere conducted on models of Piano key weirs. Three slope of the inlet key (Si = 0.7, 0.6, 0.46), three different ratios for the inlet key width to the out let key width (Wi/Wo= 1, 1.61, 1.81) and three heights (p = 30, 25, 20) cm for each weir were used. The results showed that the slope of the inlet key (0.7) gavea lowervaluesof performance efficiency and a highest values of coefficient of discharge than (0.6, 0.46) keyswhile ratios of inlet key width to the out let key width (Wi/Wo = 1.81) gave a highest values of coefficient ofdischarge. An empirical relationship was found for estimate the coefficient of discharge and performance efficiency in relation to thenon dimensionless variable
