Three-dimensional modeling of pollutants transportation in the flow field around a spur dyke

Pollutants are carried by sediment-laden flow dissolved in water or adsorbed on sediment particles. A transient three-dimensional model based on a compressible VOF (volume of fluid) method was developed to simulate the transport of dissolved and particulate pollutants. VOF is a numerical technique for acquiring and tracking the free surface of water flow. Local scouring, deposition and re-suspension were simulated and the processes of adsorption and desorption of pollutants on suspended sediment were analyzed. A series of experiments and numerical simulations were performed to study the transportation and dispersion of pollutants in the flow around a non-submerged spur dyke in a straight flume of rectangular shape. The simulation results agreed well with the experimental results. A certain volume of pollutants solution was released into the flow at upstream of the spur dyke. The concentration reduced with time. The concentration reduction was slower in the circumfluence zone than in the main flow. The ratio of adsorption to desorption coefficients was different for pollutants on suspended sediment with different diameter. The peak concentration of dissolved pollutants increased with the ratio of the adsorption to the desorption coefficients. The angle of the spur dyke affected the peak concentration around the dyke. The effect of the angle on dissolved pollutants decreased with the ratio of adsorption to desorption coefficients. The adsorption and desorption coefficients, as well as the saturated adsorption capacity had no effect on the concentration of particulate pollutants.