Approach Flow Depth Influence on Nonlinear Weir Discharge Capacity

The high hydraulic efficiency and the compactness of nonlinear weirs favor their use in several rehabilitation or new dams projects. Main types of nonlinear weirs are labyrinth and piano key weirs. The purpose of this paper is to provide indications on the influence of the approach flow depth on the discharge capacity of these nonlinear weirs. To do so, a series of experimental tests have been carried out in the laboratory of Engineering Hydraulics of the Liege University. A labyrinth and a piano key weir have been tested in channel configuration (upstream flow width equal to the weir width) considering various dimensionless dam heights. A large range of discharge has been tested for each case. The results show that the dimensionless dam height increase may decrease up to 8% of the labyrinth weir discharge capacity while it has only very limited but opposite effects for the piano key weir