The Effect of Changing Bed Roughness on the Pollution Mixing Process of Meandering

Abstract

The understanding of the mechanisms underlying the diffusion, advection, and mixing of pollutants constitutes a crucial aspect in monitoring water resources quality, particularly in the context of river systems. The longitudinal dispersion coefficient holds significant importance in predicting and illustration of pollutants in river systems. The current study investigated the advection and dispersion of pollution in meandering rivers experimentally. A series of experiments were undertaken to quantify the tracer concentration within a laboratory flume. The meandering flume with 8 bends was used to consider variation of tracer concentration for different discharges and solid and sedimentary beds. Utilizing the collected experimental data and employing the routing process, the longitudinal dispersion coefficient was determined across various segments of meandering rivers. Comparison of results for both solid and sedimentary bed indicates that as the flow discharge increases, the tracer's transfer speed increases while the transfer time decreases. Consequently, the difference between the peak concentration of tracer on the hydrographs (Cr) of input and output sections in the range of 21 to 100 percent decreases. Furthermore, by changing the bed from solid to sedimentary, Cr and the longitudinal mixing coefficient (DL) increased noticeably. In the mentioned conditions, the lowest values of Cr and DL parameters were obtained with 100 and 85% increase in value, respectively. Additionally, the results revealed a positive correlation between the mixing parameters and the length of the traversed tracer along the bends. The analysis of the data indicated that as the Reynolds number increased, the longitudinal mixing coefficient increased in both solid and sedimentary bed.

Keywords

• mixing
• routing process
• longitudinal dispersion coefficient
• meandering
• smooth beds
• sedimentary bed