Calculation Methods for the Concentration Distribution and Pollutant Mixing Zone in Rivers with Variant Lateral Diffusion Coefficient

Zhouhu Wu, Wen Wu, Zhiwen Song

Wednesday 1 july 2015

13:00 - 13:03h at Asia (level 0)

Themes: (T) Hydro-environment, (ST) Impacts of pollutants on the water environment, Poster pitches

Parallel session: Poster pitches: 9G. Environment - Impact

The range of the pollution mixing zone is a critical factor used in the design of river discharge project and in the water environmental impact assessment. For point, constant source in straight-bank wide open channel, we mathematically obtained the analytical solution of the simplified two-dimensional transport equation for the pollutant concentration distribution under variant lateral diffusion coefficient condition. Based on it, the calculation method for pollutant mixing zone was investigated. Theoretical formulas for the maximum length, maximum width and its corresponding longitudinal coordinate of the pollutant mixing zone had been deduced, as well as its area and the contour-curve formulas of its outer boundary. Further discussion had focused on the effects of variant lateral diffusion coefficient on the morphology of the pollutant mixing zone. It is found that the length-width ratio of the pollutant mixing zone is proportional to 1/2 power of the Pe number. The results of this study can be used as calculation basis of the allowable range or allowable load for river’s pollution mixing zone. It is much faster for calculation and is more flexible, convenient to use in practical engineering cases than using the two-dimensional water quality model.