Instream water quality modeling

In order to determine the impacts of a particular discharge on ambient water quality, it is usually necessary to model the diffusion and dispersion of the discharge in the relevant water body. Mathematical models can be used to predict changes in ambient water quality due to changes in discharges of wastewater. The models are typically used to establish priorities for reduction of existing wastewater discharges or to predict the impacts of a proposed new discharge. Although a range of parameters may be of interest, a modeling exercise typically focuses on a few, such as dissolved oxygen, coliform bacteria, or nutrients. Predicting the water quality impacts of a single discharge can often be done quickly and sufficiently accurately with a simple model. Regional water quality planning usually requires a model with a broader geographic scale, more data, and a more complex model structure. This chapter provides student and scientist with the basics of the processes in instream water quality modeling and comes out with some usually models used.