Downstream Local Scour of PKW with Different Shapes and Numbers of Flow Splitters

The high discharge capacity of piano key weirs (PKWs), an evolved form of labyrinth weirs, necessitates downstream scour mitigation. For the first time to our best knowledge, this study examines scouring reduction employing a Type C trapezoidal PKW with varying flow rates, tailwater depths, and flow splitter configurations (circular/rectangular; two, four, and six per cycle). Results indicated that reduced tailwater depth, increased discharge, and finer bed particles would cause enhanced maximum scour depth. Splitters lowered the maximum scour depth by an average of 13.3% (rectangular) and 7.1% (circular) compared to no splitters in gravel bed materials. Elevation of the number of flow splitters per cycle reduced the maximum scour depth, with the lowest value observed in the weir with six rectangular flow splitters. Flow splitters elongated the scour hole and shifted the maximum scour depth further from the weir toe. Finally, applying the dimensional analysis and considering the dominant parameters of bed materials, flow splitters, and flow hydraulic characteristics, relationships were derived for estimating the maximum scour depth.