Evaluation and Analysis of Crest Coefficient for Labyrinth Weir

2 Abstract: The capacity of an existing spillway can be increased by lengthening the spillway crest, or increasing the discharge coefficient or operating head, or any combination of these approaches. Constructing a labyrinth weir in an existing spillway is an example of an effective way to increases the spillway crest length and the corresponding discharge capacity for the same operating head. Thus, labyrinth weir are well suited to the sites where increasing the spillway width and maximum reservoir water surface elevation would be difficult, yet larger discharge are needed. This type of weir consists of series of slender walls having a repeating shape in plan, usually triangular or trapezoidal with vertical upstream faces and steeply slopping downstream faces. Over the past few decades, labyrinth spillways have been constructed throughout the world. Definite guidelines and theoretical procedures pertaining to hydraulic design of this type of weir not completely established. There are many factors such as head to crest height ratio, vertical aspect ratio, side wall angle, apex width and approach and conveyance channel conditions that influence the capacity of weir and hence the hydraulic design of labyrinth weir. In this paper extensive physical modeling of the labyrinth spillway, primarily flume studies, has been performed, resulting in the development of Lux and Tullis methods are compared for a given labyrinth spillway. Further testing to define labyrinth hydraulic behaviour for this lower vertical aspect ratio (w/p) is recommended.