ABSTRACT
This chapter provides a basis for understanding the various factors that affect oxygen concentrations in the Tualatin River during the early winter, and thereby provides an understanding of the capacity of the river to assimilate oxygen-demanding material during this period. It focuses on data collected during a winter sampling program that included intensive sampling of the river, its tributaries, and the wastewater treatment plants (WWTPs), averaging four to five times per week during November 1992. The chapter examines the effects of a range of flow conditions, water temperatures, and hypothetical WWTP ammonia loads on dissolved oxygen concentrations in the river. Streamflow in the Tualatin River exhibits a seasonal pattern of high flow during the winter and low flow in the summer, reflecting the seasonal pattern of precipitation. The relative significance of the various deoxygenation processes in the Tualatin River during November 1992 was evaluated by using the model in several steps.
