Jean-Louis Boillat & Sebastien Erpicum 
Labyrinth and Piano Key Weirs [PDF ebook] 

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 foundat