Experimentally Investigation of Discharge Coefficient at Trapezoidal Labyrinth Weirs

Weirs are the structures that commonly used for the regulating of water surface and control of fluid in channels and hydraulic structures. Labyrinth weirs are the types of indirect weirs that with increasing in the effective length, transmit a certain amount of flow with less upstream water surface elevation than the linear weirs. The fundamental criteria in design of labyrinth weirs is the increasing of flow conveyance capacity over the weir with constant crest and water surface elevation at the upstream of the weir. In this research, discharge coefficient of trapezoidal labyrinth weir experimentally investigated with different length and heights in flume with 15 m length and 1 m width. Results shown that, for a certain length of weir and at the constant H P t / , with increasing of weir height, discharge coefficient decreased. In the constant height andH P t / , with increasing of weir length (decrease of weir sidewall angle with the flow direction), discharge coefficient decreased. Also results show that at the constant Froud Number, the upstream water depth of linear weir is about 2.8 times more than the labyrinth weir. Furthermore, at the constant upstream water depth, conveyance discharge of trapezoidal labyrinth weir is about 2.94 times more than the linear weir. Also with use of the experimental data are provided a relationship for the trapezoidal labyrinth weir discharge coefficient.