Similar to labyrinth weirs, piano key (PK) weirs are folded in plan to increase discharge capacity for a given spillway channel width. Because of their configuration, PK weirs may be better suited than labyrinth weirs for applications where the weir footprint (length and/or width) dimensions are restricted (e.g., crest of gravity dams) as PK weirs can facilitate a significant amount of weir length relative to their footprint size. For channel applications without significant footprint restrictions, labyrinth and PK weirs may both represent viable spillway options. This paper provides an overview of some of the advantages and disadvantages of PK weirs, labyrinth weirs, and gated structures in channel applications and/or dam rehabilitation, including economic, structural, and hydraulic considerations. Two case studies are reviewed where a labyrinth weir or other type of control structure were constructed. The potential application of a PK weir was comparatively assessed for the same projects, had the option been available at the time of design.
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