Abstract: The changing law of reaeration is of great importance for predicting and evaluating the oxygen content in water and the selfpurification process of organic pollutants. The content of oxygen in natural water is a key index to assess the standard of water. As an often used physical model with good theoretical and practical values, StreeterPhelps model has been widely used to study water quality. However, in some special water areas the utilitization of StreeterPhelps model has some limitation as confirming reaeration coefficient often comes from tests in rivers with fast water flow speed with no consideration of wave effects. Furthermore, in practical research in Three Gorges Reservoir, the changing rule of COD appears abnormally. In some water areas far from pollution source, the value of COD changes with time, but does not follow the exponential attenuation rule. This phenomenon can not be explained by former modified StreeterPhelps model. However, by modifying the reaeration coefficient, a good calculation result has been obtained. Similarly, the changing rule of COD can be monitored clearly, which may also provide scientific evidence to further understand the rules of pollution ejection and sediment motion.

Key words: StreeterPhelps model, reaeration coefficient, water surface fluctuation, oxygen solubility