Investigation and evaluation of Discharge Coefficient for the trapezoidal labyrinth weir

Abstract The spillway capacity can be adjusted to increase the crest of spillway length, or increasing the coefficient discharge or effective head, or any others permutation of these approaches. In a standing spillway, a labyrinth weir constructing is a case of an active technique for increasing the length of spillway crest and as resultant increase the capacity of discharge (up to 3-4 times) for the identical effective head. Therefore, labyrinth weirs are well-matched to the sites. There are many effective factors such as width to the height of the weir which is called a vertical aspect ratio (w/p), head of water to height of crest ratio (Ht/p), angle of the side wall (α), and conditions of channel that effect on the weir capacity and labyrinth weir hydraulic design of. In this paper four different geometric variations applied to a two cycle of sharp crested trapezoidal labyrinth weir under free flow condition which include changing of vertical aspect ratio (w/P) (width to height ratio) that have effects on the hydraulic efficiency of the labyrinth weir and state the effect of the hydraulic parameter Ht/P on the coefficient of discharge (Cdw ) over weir. It was concluded that decreasing w/P has affirmative effect on the discharge capacity. On adverse it has influence of decreasing the discharge coefficient by about 20% (when increasing w/P to 1.5), while increasing it to 2.0 and 2.5 will cause more reduction to Cdw ranging from 32% to 25% for w/P=2.0 & 40% to 35 for w/P=2.5. The smaller values of the head Ht provide more discharge coefficient.