Investigating the effect of a parapet wall on the hydraulic performance of an arced piano key weir

Piano key weirs (PKWs) are classified as broad-crested weirs offering a high hydraulic performance. In this experimental study, the hydraulic performance of PKWs (of curved plan-form) under different hydraulic and geometric conditions was studied. A total of 16 experimental models with four different arc radii (35, 49, 70 and 90 cm) and central angles (90 degrees, 65 degrees, 50 degrees, 45 degrees) with a parapet wall of 4.5 cm height were considered. The results showed that by increasing the angle of the curved plan-form, the hydraulic performance of the weir was further affected by the parapet wall. Moreover, the parapet wall increased the hydraulic performance by 10% at most. In addition, the arced PKW with a parapet wall increased the performance by 2.98 and 3.82 times compared to the arced sharp-crested weir and the linear sharp-crested weir, respectively.