Simulation and Validation of Pollutant Transport in Rivers Using COMSOL Multiphysics®
Our atmosphere, land, and water are being continuously besieged by pollutants caused by such events as heavy metals leaching from mine tailing ponds, chemical spills from railroad and truck tanker accidents, and petroleum pipeline failures, to name just a few. These environmental insults are usually point generated but quickly become expanded to 2 and 3-dimensional problems, depending upon the flow regimes of surface and subsurface water bodies. Dye tracer studies have been used to develop an understanding of water feature based pollutant transport. Because they require significant time and preparation to conduct, these studies are not practical for rapid response to an event that has already happened, and much too expensive to do on a wide scale for emergency planning exercises. Dye tracer study information can be generated by simulation to add reality to emergency response and management planning related to chemical spills into flowing water bodies. Rapid estimation of a moving plume of a pollutant can be developed for real-time events if the stream geometry is readily available prior to a real event.
The COMSOL Multiphysics® platform provides the tools to relatively quickly and inexpensively provide this type of environmental engineering information. The simulation presented here is based upon a river reach of 25.5 miles and is validated using actual field measurements of a dye tracer. The COMSOL® approach to river pollution transport relies upon the Laminar Flow and Transport of Diluted Species Interfaces in a time dependent mode.
The Process Control Using a PID Controller model, in the COMSOL® Application Library, contains most of the necessary physics and settings needed and can be used as a starting template. Figure 3 displays a portion of the simulated 25.5 mile velocity field of the river, while Figure 4 shows the results of a point probe plot measuring the simulated concentration of the dye.
The Velocity Surface Plot presents results that are consistent with what one might expect from an intuitive perspective. The dye travel time by simulation and by actual measurement compare favorably. Based on these results, it is concluded that the Laminar Flow interface coupled with the Transport of Diluted Species interface provides a viable approach for dye tracer simulation and estimates of stream flow travel time.
