Linear systems theory and modeling of river water quality
Liu, Clark C.K.
The water quality of a polluted river can be improved either by increasing the river’s self-purification ability or by reducing waste loadings the river receives. Traditional physically based water quality models do not evaluate separately a receiving river’s purification ability and the effect of waste loadings; thus, they are less than desirable as an analytical tool of water quality management. An alternative river water quality modeling approach based on the linear systems theory is explored in this study. In a linear systems model, a receiving river’s self-purification ability is represented completely by the model’s impulse response function, whereas waste loadings the river receives are represented by the model’s input function. The two functions can be evaluated separately. Furthermore, the water quality condition is the system output and can be readily calculated by a simple convolution integration of impulse response function and input function. The linear systems model as a useful water quality management tool is demonstrated in this paper by applying it to a study of dissolved oxygen variations in a river which receives both point-source and nonpoint-source waste loadings.