From Labyrinth to Piano Key Weirs – A historical review

Free crest spillways are hydraulically efficient and safe in operation. Since their discharge capacity is directly proportional to the crest length several types have been developed with the purpose to increase the length of the latter. Among these types traditional labyrinth weir spillways have been studied and used for a long time. Their hydraulic performance and the effect of the involved geometrical parameters are well known. Nevertheless, their design still has to be based on experimentally derived and generalized performance curves. The recently introduced Piano Key weirs present clear advantages regarding hydraulic performance and construction costs compared to classical labyrinth weirs. Especially its small footprint makes the PK weir an efficient and cost effective solution for the increase of the flood releasing capacity at existing concrete gravity dams. Until today only preliminary design procedures are available which cannot yet be generalized. The still ongoing research on this complex hydraulic structure is a challenge for many scientists all over the world. Despite of this, several prototypes have been installed successfully over the last years on existing dams which enhance efficiently the flood release capacity

ZSE466-3 - TOPIK-TOPIK LANJUTAN DALAM GEOFIZIK USAHACARI - APRIL 1987.

ABSTRACT: The Piano Key weir (PKW) is a hydraulically attractive alternative to linear overflow weirs, increasing the unit discharge for similar heads and spillway widths. This advantage allows operating dam reservoirs on an increased level and provides thereby an enhanced retention volume. It is a result of the non-linear nature of PKWs being folded back and forth to make repeating cycles or keys. As PKWs are relatively novel structures, only few design equations are available, so that normally physical model tests of prototypes have to be conducted assuring and optimizing their hydraulic characteristics. Nevertheless, first comprehensive and systematic model test series were conducted in several laboratories. Based on such a test series, a general design equation for A-type PKWs is proposed and discussed. Considering furthermore data of other laboratory studies, the latter is validated. It turned out that main and secondary parameters exist regarding the relative effect on the rating curve. The main parameters having a significant effect on the capacity are the relative developed crest length and the relative head. The secondary parameters of small but not negligible effect comprise the ratio of the inlet and outlet key widths, the ratio of the inlet and outlet key heights, the relative overhang lengths, and the relative height of the parapet walls.