Experimental Study of the Effect of Rectangular Weir and U-weir on Contaminants’ Transverse Mixing Coefficient and Mixing Length

In the last decade, pollution and degradation of aquatic ecosystems has raised the need to develop and improve methods to enhance the transverse mixing coefficient resulting in a shorter mixing length, especially in straight open channels. In this regard, this study experimentally investigated the performance of the construction of rectangular weir and U-weir in improving water quality in an straight open channel. The experiments were performed in a 12-meter flume with a width of 80 cm. Tracer material was injected at constant rate at the upstream of weir and at different time intervals its concentration was measured simultaneously in 5 cross sections downstream of the weir at 175 nodes. In order to make the necessary calculations, the three-dimensional components of velocity were also measured. By analyzing the results and examining the transverse and longitudinal distribution of the concentration as well as the flow pattern downstream of the U-weir, it was determined that it can intensify the transverse mixing coefficient up to 12.2 times and reduce the mixing length up to 91.9% compared to the case of no weir. This is while the rectangular weir increased the transverse mixing coefficient up to 1.53 times and decreased the length of complete mixing up to 34.7% times compared to the case of no weir.