Contains the state-of-the-art on this still non-conventional hydraulic structure, and demonstrates that dam engineering currently experiences a strong revival of labyrinth oriented weirs.

Dam engineering is currently experiencing a strong revival of labyrinth oriented weirs. Labyrinth weirs, with a repetitive constructional character and an increased specific discharge capacity, are a very good technical-economical compromise. The concept of Piano Key Weir (PKW), with alveoli developed in overhangs from a reduced support area, enables the installation of non-linear crests at the top of concrete dams. As a result it eliminates the main drawback of classical labyrinth weirs, and enables their use to rehabilitate numerous existing dams. Since the first implementation of piano key weirs by Electricite de France on Goulours dam (France) in 2006, at least eight PKWs have been built in France, Vietnam and Switzerland. Their operation over a few years has already provided the first prototype data. Other projects are under study, construction or planning in varied countries. On another hand, research programs are under progress all over the world. Following a first edition in 2011, Labyrinth and Piano Key Weirs II - PKW 2013 collects up-to-date contributions from people with various backgrounds, from engineers and researchers to academics. Summarizing the last developments on labyrinth oriented weirs, the book constitutes the state-of-the-art in research and application of piano key weir solutions, and will be invaluable to professionals and scientists interested in Dams Engineering.

Labyrinth spillways are almost as old as dam engineering. In spite of the fact that they appear as a very good technical-economical compromise, only 0.1% of large dams are equipped with such weirs. The main reason for this is that traditional labyrinth weirs usually cannot be installed on top of concrete gravity dams as they require a large foundation surface. In 2003 an improved concept of traditional labyrinth spillway emerged, with alveoli developed in overhangs from a reduced support area: the Piano Key Weir (PKW). The Piano Key Weir is a weir of particular geometry, associating to a labyrinth shape the use of overhangs to reduce the basis length. The main advantage of Piano Key Weirs is that it can be directly placed on a dam crest. As a result of extreme fl oods in the recent past, a growing demand for safety in society, and revised hydrological calculations, the need for reliable spillways has consequently become higher. In this context, the Piano Key Weir proves to be an interesting solution to increase the hydraulic capacity of spillway devices.

The book contains the state-of-the-art on this still non-conventional hydraulic structure, and is divided into six main themes:

• Physical Modeling. Hydraulic capacity
• Physical Modeling. Downstream fittings
• Numerical Modeling
• Hydraulic Design
• Planned and achieved projects
• Nomenclature, Database, Future developments.

The papers in Labyrinth and Piano Key Weirs demonstrate that dam engineering currently experiences a strong revival of labyrinth oriented weirs, and are particularly of interest to academia, researchers and professionals working in the area of hydraulic engineering, and to dam control authorities and dam owners.

Since the first implementation by Electricite de France on the Goulours dam (France) in 2006, the Piano Key Weir has become a more and more applied solution to increase the discharge capacity of existing spillways. In parallel, several new large dam projects have been built with such a flood control structure, usually in combination with gates. Today, more than 25 Piano Key Weirs are in operation or under construction all over the world. More than 15 years of research and development have enabled detailed investigations of the hydraulic and structural behaviour of the Piano Key Weir complex structure and have provided more and more accurate design equations. Following the proceedings of the first two workshops held in Liege (Belgium - 2011) and Paris (France - 2013), Labyrinth and Piano Key Weirs III collects the contributions presented by people with varied background, from researchers to practitioners, at the 3rd International Workshop on Labyrinth and Piano Key Weirs - PKW 2017 (22-24 February 2017, Qui Nhon, Vietnam). The papers, reviewed and accepted by an International Scientific Committee, summarize the current state-of-the-art on Piano Key Weirs from a theoretical to a practical point of view, and present most of the main projects in operation or under construction. Labyrinth and Piano Key Weirs III is thus a reference for students, practitioners and researchers interested in Dams Engineering.