Numerical simulation of reaction-diffusion process about sewage discharge in Yangtze Estuary

Two representative variables of point source sewage discharges, the reaction-advection-diffusion dominated process as manifested by chemical oxygen demand (COD) and the reaction-diffusion dominated process as manifested by dissolved oxygen demand (DO), were obtained and analyzed as water quality variations by application of the Environmental Fluid Dynamics Code (EFDC) with solutions for hydrodynamics during tides in Yangtze Estuary. The simulated increments and distribution of COD in the water show acceptable agreement with field observation. The concentration of DO in the North Branch is much higher than in the South Branch due to consumption of oxygen in the South Branch resulting from discharge of sewage from Shanghai. The DO concentration of the surface layer is greater than that of the bottom layer. The DO concentration is low in areas with a depth less than 20 m, and high in areas between the 20 m and 30 m contour lines of depth. It is concluded that the numerical model is valuable in simulation of water quality in the case of specific point source pollutant discharge.