Experimental Study on Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs

Weirs have important roles in dam safety and should spill floods with high return period. The designers enhance the width of the weirs to increase the discharge capacity. In some cases, this procedure has topography and economic limitations. Labyrinth weirs can be considered as an alternative. This structure is recommended also for modification and increasing the capacity of the existing spillways. However, for reservoir applications, the cycle configuration may be arced to improve the approach flow conditions to each cycle and further increases the weir crest length. In this study, the hydraulic performance of arced weirs located in a reservoir has been studied experimentally. In the first step, dimensionless parameters affecting the performance of arced weirs is introduced using Buckingham π theorem. Laboratory observations such nappe aeration, flow mound, local submergence and non-uniform performance of cycles in labyrinth weirs are presented and discussed. Data analysis has been done based on the measured values, laboratory observations and the results of previous researches. Despite the negative impact of local factors such as flow mound and local submergence, results indicates that the arced linaer weir can improve efficiency up to about 47%. This amount can reach up to approximately 350% using the arced labyrinth weir. Finally, based on the results and limitations of this study, a method is presented for the design of weirs located in the reservoir. By using this method, the designer can find the geometric parameters of the weir for passing a certain flow rate in a given hydraulic head. However, this method can be used as a first order approximation. However, more tests are required to ensure whether this method is appropriate under other circumstances.

Experimental Study on Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs Keywords:

Dam , arced weir , labyrinth weir , discharge , flow mound , local submergence