Application of Modified Streeter-Phelps Model and COD Changing Model to Xiangxi River in Three Gorges Reservoir Area

As an often used physical model with good theoretical and practical values, Streeter--Phelps model has been widely used to research water quality at present. However, in some special water areas the utility of Streeter--Phelps Model suffers limitations because confirming reaeration coefficient often comes from tests in rivers with fast water flow speed rather than considering the wavy effects. Furthermore, in practical research in Xiangxi River in Three Gorges Reservoir Area the changing rule of COD appears abnormity. In some water areas far from pollution source the value of COD changing with time doesn't accord with exponential attenuation but slightly sways in a certain value. This phenomenon can not be explained by former modified Streeter--Phelps models. After research it indicates that through modifying the reaeration coefficient good calculation results will be obtained. Similarly, the changing rule of COD not only can be made clear but also can provide scientific evidence to further studying rules of pollution ejection and sediment motion.