Hydraulic modelling of Piano Key Weirs: a composite approach

During the last few years, several piano key weirs (PKWs) have been built in France and abroad. Thanks to the reduced footprint and high release capacities of this new type of weir, making it particularly suited for concrete dams rehabilitation, lots of other projects in various countries are under construction or study. The prototype use of PKW requires knowledge about its structural behaviour, hydraulic capacities as well as integration into dams’ environment. This paper aims at presenting numerical and physical modelling works performed at the University of Liege to address the last two items. In particular, large scale physical modelling and parametric scale models have enabled to understand the hydraulic behaviour of the structure and to highlight its most influencing geometric parameters as well as their best variation interval depending on various criteria related to the weir design (discharge efficiency, cost...). A 1D numerical model has also been developed based on these experimental investigations. It enables to predict in a few minutes, with 10% accuracy, the discharge capacity of a given PKW geometry within its usual range of operation head. This model, available as a freeware from http://www.pk-weirs.ulg.ac.be, constitutes a key tool for the first design of such weirs. Finally, the scale model studies of major projects such as Raviege dam (France) for Electricite de France EDF and Ouldjet Mellegue Project (Algeria) for Coyne et Bellier – Tractebel Engineering enable to confront theoretical predictions with experimental results and to address the problem of PKW integration on dam crests.