Effectiveness of Various Protection Works to Minimize Scour Downstream of a Piano Key Weir

Scour protection measures are often required to maintain the stability of in-channel hydraulic structures during flood events, yet minimizing the footprint of a concrete apron in a river is environmentally desirable. Thus, this study systematically investigated scour at the base of a Type A piano key weir and the performance of different scour protection measures for a noncohesive material via a large-scale physical model. Five scenarios were considered: (1) no protection, (2) a horizontal apron and cutoff, (3) a horizontal apron and cutoff with a rock sill, (4) a horizontal apron and cutoff with riprap, and (5) a horizontal apron and cutoff with a bed sill. The effectiveness of each scour protection measure was compared with the no protection scenario and corresponding scour profiles. The results indicated that maximum scour depths can be reduced by as much as 70%, giving flexibility regarding various scour reduction measures downstream of this in-channel structure.