Author(s): Rajib Kamal; Samantha Barnes; Soren Jensen; Christina James

Linked Author(s):

Keywords: Streams and rivers; Transverse mixing; Regulatory mixing zone; Bends; Analytical modeling

Abstract: A regulatory mixing zone (RMZ) allows initial dilution of industrial and municipal wastewater discharges which is typically limited to shorter extents. For natural streams, transverse mixing is the primary mechanism for dilution and dispersal of effluent within this extent. The effect of in-stream local flow features and nonuniformity on the variation of transverse mixing is the focus of this study. The work was carried out through a combination of field measurements in a RMZ of a small stream and analytical modeling. The analytical technique was developed to evaluate the tracer measurements using the streamtube method based on cumulative discharge concept and the method of moments and modified for application to low-flow conditions. The resulting transverse mixing coefficients were analyzed with respect to channel geometry and local features observed in the field. The estimated mixing coefficients deviated considerably compared to traditional literature values indicating strong influence of the local features. Results indicated rapid mixing due to a sharp bend and shallow rapids significantly enhanced transverse mixing within a relatively shorter RMZ extent, with the mixing coefficient nearly doubled compared to expected value from literature. This study demonstrates that transverse mixing within a shorter extent of effluent discharge varies directly with respect to local features and highlights the importance of field-based measurements and verification through appropriate analytical tools for RMZ analyses.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1693-cd

Year: 2023