# COMPUTATION OF MINIMUM DO (Cont)

The value of k1 if generally taken to be the same as the rate constant for the BOD reaction in this equation BODt = BODL X (1-10-kt); it can be determined in the laboratory. The value of k2 depends on the velocity and the depth of the flow and can be determined from field studies or by an appropriate formula. The reaeration rate constant k2 can be vary from about 0.1 for the sluggish to about 4.0 for a swallow turbulent stream. Both rate constants, k1 and k2 depend on temperature.

The equation tc and Dc look complicated, and they are. They are presented here to illustrate the power of mathematics as a tool for modeling the environment and helping solve water pollution problems. But as complicated as they may appear, the Streeter-Phelps equations are not completely accurate representations of the oxygen profile in a polluted stream or river. Other factors that affect the oxygen balance include photosynthesis and respiration of rooted plants and algae and the oxygen demand of benthic (bottom) deposits. Equations that have been developed to include these factors are even more complicated than the equation tc and Dc