The effect of increasing the number of cycles on the performance of labyrinth side weir H. Zahedi Khameneh n , S.R. Khodashenas, K. Esmaili Water Engineering Department, Ferdowsi University of Mashhad, Iran article info Article history: Received 26 March 2013 Received in revised form 3 May 2014 Accepted 11 May 2014 Available online 14 June 2014 Keywords: Labyrinth side weir Discharge coefficient Water surface profile Experimental test Number of cycle abstract 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 C m . Also, upon comparison with rectangular weirs, labyrinth weirs increase C m 1.5 to 3 times and 30% in comparison with modified oblique side weirs (in all cycles). & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Side weir is a fixed structure on one side or both sides of the main channel. When the water surface reaches a certain level (weir crest), the extra water flow flows on the side weir. The inundation in this structure is gravitational and it is widely used because the transferred flow is continuous and no extra energy is spent to transfer water (such as pumping stations). These weirs are used in irrigation and drainage channels or in sewage transfer channels. It is also used as a deviatory structure in rivers and channels in order to control the flow. Moreover, it is also used as a protective structure in reverse siphons upstream and under- pass of the roads. In the most usual form of side weirs, the rectangular weir is placed in the channel parallel to the flow direction. In this mode, the side weir (water transfer channel) is at an angle with the main channel. The type of the flow on the side weir is locally variable with flow decrease. The locally variable flow is a mode of continual flow where flow intensity increases or decreases along the path. The flow in side weirs is basically a branch flow. Flow distribution is done along the flow path. Numerous theoretical and laboratory studies have been conducted to investigate the energy changes along the branch flow. Most of the researchers believe that energy should be considered constant along the path. They believe that the branch- ing of the flow does not lead to energy reduction or that the amount of energy reduction is negligible compared to the reduc- tion caused by friction. The studies conducted by De-Marchi in 1934 [3] can be considered as the base and foundation of this theory and also subsequent studies on side weirs. De-Marchi presented a relationship for the flow on these weirs using the energy equation, assuming that the specific energy is constant along the side weir.  dQ dx ¼ 2 3 C m ffiffiffiffiffi 2g p ðy  wÞ 1:5 ð1Þ In Eq. (1), dQ =dx is the flow change along the weir, C m is the discharge coefficient of the side weir (De coefficient), g is the gravitational acceleration, y is the flow depth, and w is the height of the weir. De-Marchi stated that the discharge coefficient of side weirs is a function of hydraulic and geometric and flow variables and De- Marchi presented a relationship to obtain the length of the weir. L ¼ 3 2 B C m ðφ 2  φ 1 Þ ð2Þ in which L is the length of the weir crest; B is the width of the main channel; C m is local discharge coefficient known as the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/flowmeasinst Flow Measurement and Instrumentation http://dx.doi.org/10.1016/j.flowmeasinst.2014.05.002 0955-5986/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ98 915 3177935. E-mail addresses: h.zahedi.kh@Gmail.com (H. Zahedi Khameneh), saeedkhodashenas@yahoo.fr (S.R. Khodashenas). Flow Measurement and Instrumentation 39 (2014) 35–45