The influence of submergence on scour at triangular piano key weirs

Abstract Abstract: This research investigates scour dynamics downstream of triangular piano key weirs (PKWs), which can cause significant channel bed erosion. The study analyzed scour effects under four discharge conditions and varying submergence ratios in fine gravel and medium gravel beds within a 10 m long, 0.75 m wide, and 0.80 m high channel. Findings reveal that 49.5% increase in the particle Froude number and a 54.2% decrease in submergence ratio in the fine gravel bed resulted in a 270% increase in maximum scour depth and a 114.2% increase in scour hole length. The scour depth in the fine gravel bed was 43.83% greater than in the medium gravel bed, with a 47.69% increase in average scour hole length. Higher submergence ratios reduced the intensity of downstream hydraulic jumps and sediment scouring, leading to significant decreases in maximum scour depth (81%), maximum scour distance from the weir toe (66%), scour hole length (80%), and weir toe scour depth (84%) compared to free flow conditions. Consistent scour hole profiles were observed across experiments, and a non-dimensional predictive equation for these profiles achieved a high R² value of 0.920. The research also introduces new equations for estimating scour characteristics at triangular PKWs under both free and submerged flow, with strong predictive capabilities. By identifying key parameters influencing scour, this study aids in optimizing PKW design to reduce erosion and enhance the stability of hydraulic structures.