Calculation Method of Lateral and Vertical Diffusion Coefficients in Wide Straight Rivers and Reservoirs

The study is financially supported by the National Natural Science Foundation of China (50979036), and by the Foundation of National Water Pollution Control and Governance of China (NO. 2009ZX07210007-01). Abstract—In the calculation of mixed-transport capacity of pollutants which were discharged from bank outfall of wide straight rivers or reservoirs, the lateral diffusion coefficient can better demonstrate the mixed-diffusion characteristics near the bank than the transverse diffusion coefficient. For deep rivers and reservoirs, the vertical diffusion coefficient is one of the important water quality parameters. Based on the theoretical calculation method of pollutant mixing zone, the unified equations of the standard curve and curved surface outside the borders of pollutant mixing zone were deduced, including the characteristic parameters of maximum length Ls, maximum width bs and maximum depth ds et al. The shape of curve is akin to semi-elliptic, and the shape of curved surface is akin to part ellipsoid, which is similar to the pollution of the mixing zone. The calculation equation of lateral diffusion coefficient or vertical diffusion coefficient which was determined by the maximum length and maximum width or maximum depth of the outer boundary of pollutant mixing zone near the discharge outfall and the mean velocity were put forward in this paper. The calculation method of the lateral diffusion coefficient or vertical diffusion coefficient which was overall controlled by the area or volume of pollutant mixing zone and the practical method of vertical diffusion coefficient which was determined by the concentration of surface transverse integration was proposed in the paper. The lateral diffusion coefficient of the downstream of Guangfu River in low water season was given, which was 0.27 m/s by analyzing the data from field observation.