The effect of increasing the number of cycles on the performance of labyrinth side weir

• More zigzag along the main channel side weir makes water surface more uniform.
• Amount of energy along the weir has fallen by increasing number of cycle.
• Labyrinth weirs increase Cm value 1.38–2.8 times compared to conventional weirs.
• Labyrinth weirs raise Cm value 1.2–1.7 times compared to modified oblique weirs.

Side weir is one of the most common hydraulic structures, which is used as a deviatory structure in rivers, irrigation and drainage channels and also in urban sewage collection systems. One of the ways to improve the efficiency of the performance of the side weir is changing the geometry of the weir.The effect of deformation and cycle number increase on the hydraulics of the flow was investigated in the side weir, through conducting 360 experiments on the labyrinth weir in three cycles 2, 1 and 4 and the discharge coefficient was obtained for different modes. The results showed that cycle number increase leads to the reduction of flaws such as Eddy flows, decrease of weir input and sudden flow increase along the weir and it also reduces the projection length of the weir. The results indicated that the weirs with cycles 1 and 2 have higher Cm. Also, upon comparison with rectangular weirs, labyrinth weirs increase Cm 1.5 to 3 times and 30% in comparison with modified oblique side weirs (in all cycles).