Fuzzy Comprehensive Evaluation of Water Quality at Monitoring Points : Application to Lake Biwa

抄録

A method for comprehensively evaluating water quality at various points in a water body has been developed based on the fuzzy reasoning. Vagueness in borders of conventional water quality classes formed for each water quality index is quantified by introducing fuzzy sets associated with the classes and nonlinear membership functions. Mamdani method (or min-max-center of gravity method) is employed in the fuzzy reasoning in order to synthesize concentration data on multiple water quality indices. The evaluation method developed in this study can represent the state of water quality at each points with a real number ranging from 0 to 100. The applicability of the method is demonstrated with the series of monthly observed data from April 1980 to March 2010 at 49 monitoring points in Lake Biwa, Japan. Temporal and spatial variations of the synthesized water quality scores at the monitoring points are presented. The application of the fuzzy comprehensive evaluation method would lead to more rational comparison of synthesized water quality at MPs in the lake and to producing useful information in decision-making on water quality management in the water body.