Effect of pollutant decay on steady-state concentration distributions in variable depth flow

Pollutants discharged together in a variable-depth flow can separate laterally if the decay mechanisms differ e.g. evaporation is more effective in shallow water, but floc breakup is more effective in deeper faster flow. Ray tracing of concentration information away from a point source (similar to mathematical optics) is used to quantify the effects of decay. The concentration reduction rate along a ray increases with decay rate divided by flow speed and with angle between the flow and information directions. Pollutant concentrations tend to fractionate towards regions of smaller decay rate divided by flow speed.