Discharge coefficients for free and submerged flow over Piano Key weirs

A comprehensive experimental investigation was performed to better understand the effect of the weir geometry of a Piano Key weir (PKW) on the discharge coefficient for both free and submerged flow conditions. Experiments were conducted in a 12 m long, 0.4 m wide and 0.7 m deep rectangular glass-walled flume. The effects of the PKW geometry, including weir length and height, up-and downstream key widths as well as up-and downstream apex overhangs on the weir flow discharge coefficient were investigated, so that the governing weir head-discharge relationship resulted. In addition, on the basis of a comprehensive data set, practical discharge coefficient relations associated with the standard weir equation were proposed for both free and submerged flows over PKWs. The present correlations cover various types of PKWs. From the experimental data, optimum values of the primary dimensionless weir parameters result produce the maximum discharge efficiency.