Mixing effects in the river downstream from pollution discharge point
Autor
Bielski, Andrzej
Opublikowane w
Technical Transactions
Numeracja
Vol. 118, iss. 1
Data wydania
2021
Miejsce wydania
Warsaw
Wydawca
Sciendo
Sekcja czasopisma
Environmental Engineering
Język
angielski
eISSN
2353-737X
DOI
https://doi.org/10.37705/TechTrans/e2021004
Słowa kluczowe
pollution, mixing, river, point sources, velocity distribution, concentration distribution
Abstrakt
This paper follows the propagation of pollution in a river with a rectangular crosssection of the river bed and a variable cross-sectional velocity. The calculations were made for steady flows and steady pollutant concentrations. To approximate the velocity distribution in the river bed a set of equations for current and vorticity functions was solved. The distribution of pollutant concentrations in the river was calculated from a bidirectional advection and turbulent diffusion equation. Analysis of the distribution of concentrations leads to the conclusion that the effects of transverse advection associated with a lateral inflow of pollutants disappear relatively quickly. Therefore, the distribution of concentrations in cross sections further downstream from the point of pollutant discharge can be determined quite accurately just from an advection-diffusion model, with no transverse advection effects included. Such a level of accuracy is usually sufficient to assess the impact of a pollution source on the aquatic environment. The transverse mixing of pollutants in the stream proceeds slowly and creates a large mixing zone in which the concentrations of pollutants (low but still significant for water quality) can be detected in cross-sections that are remote from the pollutant discharge point. Transverse advection may be ignored while calculating concentrations in remote cross sections at straight watercourse sections and in steady state conditions.
