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...