Labyrinth weirs are one of the kind of nonlinear crest weirs causing the increase of discharge capacity for specified height of water level in canals and dams. In this study, the effects of dentate and orifice labyrinth weirs on increasing the discharge capacity were investigated. Experiments were conducted in a laboratory flume with length of 12 m and width of 0.8 m. The nine experimental models with 15 cm height were used. The results showed that for L/W=2 and H/P=0.2, the discharge coefficient of the orifice-dentate labyrinth weir and the dentate labyrinth weir are 75.6% and 17.5%, more than the simple labyrinth weir, respectively. However, dent and orifice may decrease their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes was increasing the flow interference in downstream of labyrinth weir between dents, orifices and weir with increasing discharge. Also, the result showed the efficiency of orifice and dentate on labyrinth weirs will decrease with increasing the weir magnification (L/W) and they lose their effect.
