Piano Key Weirs: the experimental study of an efficient solution for rehabilitation

Abstract

The Piano Key Weir (PKW) is a particular geometry of weirs associating with a labyrinth shape and the use of overhangs, which reduce the basis length. The PKW could thus be directly placed on a dam crest. Together with its important discharge capacity for low heads (up to four times that of a Creager weir), this geometric feature makes the PKW an interesting solution for dam rehabilitation. The PKW is a new type of weir, first designed in 2001 and built for the first time in 2006. Even if the first experimental studies confirmed its discharge capacities, there is still a lack of understanding of the flow behaviour upstream, along and downstream from this complex structure. An experimental research, started in 2008 at the Laboratory of Engineering Hydraulics of the University of Liege, will provide contributions to the study of the flow behaviour on large PKW scale models, along with a geometric parameters analysis on models with variable geometries. These studies will enable one to define efficient and scientifically based design rules. This paper presents the strategy and main goals of this four-year study. These goals are also illustrated based on the first results obtained from experiments carried out on large scale models of PKW. The hydraulic behaviour of the structure is clarified based on measurements of water depths, pressures, velocities and discharges on each part of the weir.