Piano Key Weirs (PK Weirs) triple the spillways discharge

Posted on June 20, 2015 in Piano Keys Weirs

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Tested since 15 years and implemented on many dams in various countries since 10 years, this improved labyrinth design appears very cost efficient, optimizing hydraulic efficiency as well as structural requirements and construction facility.

The layout of walls has a rectangular shape, part of the walls is overhanging and those walls along the flow are inclined. This is hydraulically favourable and allows the base width of the structure to be reduced, thus allowing its utilization upon most spillways or gravity dams. The here below figures show a typical design of symmetrical PKWeir with proportions based on “Pm” which is the maximum height of the labyrinth walls. Other configurations may be used case by case according to the local conditions (For instance, only one upstream overhang, or only one downstream overhang, or no overhangs, etc..).

Plan view

Cross section 1-1 (outlet)

Cross section 2-2 (inlet)

Flow discharge on model

Van Phong dam (Vietnam)

For a water upstream head over the weir crest”h”between 0.4 Pm and 2 Pm and a ratio between the developed plan length of wall and the overall spillway length close to 5, the discharge (in m3/sec) per metre of spillway is close for the model above to
4.3 h√Pm as compared to 2.15 h√h for a Creager Weir.

More details are given in Appendix 2 of ICOLD Bulletin n° 144.

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