ABSTRACT
This chapter emphasizes modeling stream water quality, as influenced by stream regulation, rather than modeling water quality of deep storage impoundments built on streams. It examines the structure of stream water quality models, the model processes, the types of stream water quality models, model application, and model selection. Models can be physical, mathematical, or conceptual in nature. Mathematical models (the general class of models used for water quality modeling) are formal expressions of relationships between defined entities expressed in mathematical or quantitative terms. Mathematical models may be loosely categorized into one of two types, mechanistic or empirical. The chapter focuses on mechanistic, deterministic simulation models for stream water quality. Water quality conditions are generally predicted and not specified for the downstream boundary, although specification of water surface elevations, flows, or a rating curve is required for a hydraulic routing model. Specification of flow and constituent concentrations at all upstream and inflow boundaries is required.
