ABSTRACT
ABSTRACT: Similar to labyrinth weirs, piano key weirs (PKW) are folded in plan to increase discharge capacity for a given spillway channel width. Because of their configuration, PKW are better suited than labyrinth weirs for applications where the weir footprint (length and/or width) dimensions are restricted (e.g., crest of gravity dams). PKW can facilitate a significant amount of weir length relative to their footprint size. For channel applications without significant footprint restrictions, labyrinth and PKW may both represent viable spillway options. Gated spillways can typically pass a higher unit discharge than passive flow control structures (e.g., labyrinth and PKW) due to the resulting low crest elevation that occurs when the gates are opened. Gated spillways are effective at passing flood events but rely onmanual or automated operation. This can be particularly challenging for manually operated gates at remote dam sites. Labyrinth, PK, and gated weirs all have their place in spillway design. This paper evaluates some of the advantages and disadvantages of each in channel applications for dam rehabilitation with respect to economic, constructability, operational, and hydraulic considerations. The cost estimates included in the evaluation consider the complexity of each structure and the application to different constraints. Comparisons are limited to a single PKW geometry.
