Evaluation of Appropriate Advective Transport Function for One-Dimensional Pollutant Simulation in Rivers

Water quality prediction is a valuable tool for pollutant control in aquatic environments. A river system is selected and one-dimensional flow is assumed for the simulation of pollutant transport in this paper. Advective and diffusive terms of transport equation are considered separately. Different functions of advective transport are proposed and applied for a specified velocity on the discrete cells along the river and compared with each other. Abilities and flexibilities of these proposed functions are investigated and the compatible one is determined for the point source pollutant transport in the channel. Fluctuations (Maximum content of negative concentrations), tolerances (Maximum interval of negative concentrations) and attenuation (Decreasing peak of the pollutant distribution) are selected for this purpose. Quick and the proposed functions including trigonometric, simple exponential, symmetric exponential and quadratic exponential of advective transport are selected for the comparison. Results show that during the simulation period (times up to 100 seconds and times more than 100 seconds), for the estimation of attenuation, the peak of the pollutant distribution and the elimination of fluctuations and the tolerances, the proposed symmetric exponential and quadratic exponential functions of advective transport perform better than other numerical methods and presented functions. Also for all these scales both of quadratic exponential and symmetric exponential functions act similarly, therefore they can be used frequently for the simulation of pollutant transport in rivers without creating negative concentration.
Moreover, simple exponential function and quick method identically predict the peak of pollutant chemograph at each downstream point.