Linear systems approach to river water quality analysis
Liu, Clark C.K. and Jenny Jing Neill
The water quality of a polluted river can be improved either by increasing the river’s self-purification ability or by reducing the amount of waste loading the river receives. Traditional physically based water quality models do not evaluate separately a receiving river’s purification ability and the effect of waste loading; thus, these models are not ideal analytical tools for water quality management. This chapter introduces and discusses an alternative river water quality modeling approach based on the linear systems theory. In a linear systems model, a receiving river’s self-purification ability is represented completely by the model’s, impulse response function, whereas the amount of waste loading the river receives is represented by the model’s input function. These two functions can be evaluated separately. Further, a simple convolution integration of these two functions gives the system output. Usually, the system output is the water quality condition of the receiving river. The linear systems model’s usefulness as a water quality management tool is demonstrated in this chapter by applying it to studies of dissolved oxygen variations (1) in a steady-state river system that receives both point-source and nonpoint-source waste loading and (2) in a time-variable river system that receives point-source waste loading in the form of periodic function.