Dissolved oxygen (DO) depletion in receiving streams during combined sewer overflows (CSO) is aphenomenon which comprises dry weather processes, including photosynthesis, and wet weather impacts. During a CSO event a distinction between immediate and delayed DO consumption in the stream caused by biodegradation of soluble and particulate organics, respectively, is made.
Two DO models have been developed in order to simulate the combined dry weather and wet weather effects. The first one is a simplified model based on the concept of an extended Streeter-Phelps equation and the second one is an advanced model, which is made from two integrated parts a hydro dynamic and a transport-dispersion model. The structure of the two models is described and model results are compared and evaluated.