Local scour downstream of various shapes of piano key weirs

This research investigated the local scour downstream of Piano key weirs (PKWs) with various shapes in plan, including rectangular, trapezoidal, and triangular. The experiments were conducted under various flow conditions with two different bed material sizes. The findings revealed that the scour parameters downstream of the PKW models followed similar patterns, albeit with variations in the maximum values of scour depth, scour hole length, scour hole area, and scour hole volume. The trapezoidal Piano key weir (PKW) exhibited a decrease of 10.7, 9, 14, and 8% in the parameters mentioned above compared to the rectangular PKW and a reduction of 20.5, 24, 31, and 26.5% compared to the triangular PKW, respectively. The scour index of the rectangular PKW, trapezoidal PKW, and triangular PKW are in the range of 0.78-1.87, 0.69-1.84, and 1-2.40, respectively. Moreover, the trapezoidal PKW demonstrated average values of asymmetry index, which were 3.62% higher and 9.21% lower than those of the rectangular and triangular PKWs, respectively. The influence of the PKW shape on the downstream scour hole slope and area was more significant compared to its effect on the upstream scour hole slope and volume.