Similar to labyrinth weirs, piano key (PK) weirs are folded in plan to increase dischargecapacity for a given spillway channel width. Because of their configuration, PK weirsmay be better suited than labyrinth weirs for applications where the weir footprint (lengthand/or width) dimensions are restricted (e.g., crest of gravity dams) as PK weirs canfacilitate a significant amount of weir length relative to their footprint size. For channelapplications without significant footprint restrictions, labyrinth and PK weirs may bothrepresent viable spillway options.This paper provides an overview of some of the advantages and disadvantages of PKweirs, labyrinth weirs, and gated structures in channel applications and/or damrehabilitation, including economic, structural, and hydraulic considerations. Two casestudies are reviewed where a labyrinth weir or other type of control structure wereconstructed. The potential application of a PK weir was comparatively assessed for thesame projects, had the option been available at the time of design.
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