The Effect of Height and First Roughness Distance on Energy Dissipation in Piano Key Weirs

Along with the numerous developments and facilities for constructing large dams, there is a need for developing design and construction methods for systems that can correctly discharge the floods. Weirs refer to any barrier across a channel that raises the flow level and accelerates the flow when flowing over it (Abrishami and Hoseini, 2011). Piano key weirs are the newest type of long-crest weirs and one of the best solutions for modifying the existing weirs. Reducing the energy of the flow over the weirs before their transfer downstream is a solution for preventing possible damage to the structure itself and downstream structures as well as the excess costs incurred by the builders of hydraulic structures due to constructing strong protective structures (Katourani, 2012). Lempèrière and Ouamane (2003) described the piano key weirs and stated their advantages compared to other conventional nonlinear weirs as the ability to place the weir in the crest of the reservoir dam and thus increasing the specific flow rate. Erpicum and Machieles (2011) compared the energy dissipation between two different geometries for a piano key weir and a spillway weir. Concerning the application of a block, the tests and results obtained by the US Land Renewal Organization indicate that using large blocks that separate the flow jet and create turbulence can effectively dissipate the kinetic energy of the current.