The simulation of water quality in the Waikato and Tarawera rivers.
The causes and effects of water pollution are Listed and the mechanisms of stream self-purification described. The parameters for which mathematical models have been developed are described and the success of the various previous models for predicting them is discussed. The equations governing the concentration of dissolved oxygen in a polluted waterway are developed and a review is made of the various finite difference schemes which available for solving them.
Models are developed for predicting dissolved oxygen concentrations in two polluted New Zealand rivers, the Waikate and the Tarawera. It was found that the models used previously in other waterways were not adequate for either of these rivers. The model of the Waikato River uses the well-known Streeter-phelps equation to model the exertion of BOD but includes the effects of the macrophyte and phytoplankton communities on the concentration of dissolved oxygen. The model of the Tarawera River uses the Monod equations to predict the concentrations of active biomass in the porous pumice sediments on the river bed, and successfully accounts for the high rate of oxygen uptake which has been observed. The way in which these models could profitably be developed is also discussed.