The rearation coefficient is most commonly a function of temperature, stream velocity, stream slope and stream depth. In the absence of sources and sinks, the concentration of a conservative substance does not change along the length of a river. Dispersion is the least important mixing process in river modeling. The Thomas method is used to estimate CBOD settling rates. CBOD and NBOD can be combined into a single pollutant term when the settling rates are equal.
Deep rivers are most susceptible to effects of sediment oxygen demand.