Experimental study of the geometric effect of trapezoidal labyrinth weirs on increase of the dissolved oxygen

The amount of dissolved oxygen (DO) in water is an important parameter of rivers water quality. Installation of weirs in channels is one of the methods entering air babbles into the falling water and increase DO. In this research, the performance of trapezoidal labyrinth weirs was investigated as compared with the linear weirs under various geometries and hydraulic conditions in terms of DO Experimental observations and result analysis showed that the length of cycle in the flow direction, thickness of weirs and nappe patterns are three effective parameters on DO amount in trapezoidal labyrinth weirs. The results of this study indicated that the three cycles-labyrinth weirs had better performance compared to two cycles-labyrinth weirs. Also, the results showed that the three cycles-trapezoidal labyrinth weirs with the lower length in the flow direction at low relative head and with the longer length in the flow direction at high relative head had the best performance in terms of DO that increased 58 and 44 percent, respectively. The results of this study indicated that, by increasing the ratio of falling height to weir height from 0.4 to 0.8, the DO efficiency increases (13%) by labyrinth weirs.