A Laboratory Study of Local Scour and Driftwood Effects at a Type A Piano Key Weir

Piano key weirs are a unique weir designed to increase the amount of flow that passes over it via its zig-zag shape (similar to the rectangular shape of keys of a piano). With its relatively small footprint, they are becoming more popular to upgrade existing water management projects and are also being used in new construction works. However, there is little information available regarding how these weirs handle sediment and driftwood. Additional information will help researchers and designers to understand the challenges of upstream sediment buildup, driftwood accumulation, and the effects of floods on downstream scour with viable protection measures. Therefore, experiments were conducted in the laboratory to analyze these behaviors. This data was complimented by information from computer models. These results showed that these weirs have the ability to transport sediment from upstream to downstream reach without human removal. Similarly, driftwood accumulation against the weir, which can sometimes clog waterways, in fact enhanced the sediment removal. Results from experiments were used to test the physics-based prediction model which was validated, facilitating estimation of scour as a function of time. This model hence unfolds critical results for engineers and practitioners in designing the structures. In addition, studies performed using protection measures showed effective reduction of scour depth with concrete slabs and with large rock that helped reduce structural vulnerability from toe scour.