Theoretical documentation for the pollutants fate model in a river "Heridanos"

"Heridanos" is a water quality model which examines the fate of most important pollutants in a river. The model comprises three separate submodels, running successively at each time step. The first module solves the full one-dimensional St. Venant equations, in order to determine the flowing conditions, that is, the velocity and the water depth. The second submodel solves the advection-dispersion equation in order to account for the transport phenomena of dissolved substances along the river. The third is a water quality submodel which describes with simple equations, the main physical, chemical and biological processes taking place in the water column, like growth, respiration and death of heterotrophic organisms and algae, nitrification through the growth of two-stage nitrifiers, hydrolysis and reaeration. The model is able to predict at each time step, the concentration of every substance along the river. The substances being modeled are several forms of nitrogen and phosphorus, dissolved oxygen, heterotrophic biomass, algae and conservative substances. This report is the scientific documentation of the model "Heridanos".