Hydraulic behavior of Piano Key Weirs: experimental approach

The Piano Key Weir (PKW) is a particular geometry of weir similar to a labyrinth shape that features overhanging cycle ends to reduce the base length. Together with its high discharge capacity for low heads, this geometric feature makes the PKW an interesting solution for dam rehabilitation, permitting the placement of the weir directly on dam crest. However, PKW stays a new type of weir, firstly designed in 2001 and built for the first time in 2006 by Electricité de France (EDF). Even if the first experimental studies confirmed its discharge capacities, lacks persist in the understanding of the flow behaviour upstream, along and downstream of this complex structure. This paper presents the mean results and observations obtained from experiments on a large scale model of PKW. The hydraulics of the structure is clarified based on measurements of water depths, pressures, velocities and discharges on each part of the weir. These observations explain the effect of geometric improvements proposed in former studies.