Abstract: The decision-making using comparison of stream water quality prescribed limits with various water quality indices has been developed to integrate water quality variables. This approach has few drawbacks such as some parameters in the index equations can influence the final score of WQI dramatically without valid scientific justification. There are limitations on which a wrong decision can be taken as it is dependent on the fix weight age assigned to different parameters, where as the weight age should be varied on the basis of season, rainfall, ambient temperature and other environmental factors. These indices are lacking to deal with uncertainties involved at various steps indecision-making. One way of avoiding the difficulty in uncertainty handling in water quality assessment is to introduce a margin of safety or degree of precaution before applying a single value to quality standards as the same technique was also used by other workers in the field of environmental sciences. These methodologies based on fuzzy sets theory are tested with real environmental problems to handle the uncertainty in imprecise environment in decision-making tools. It is proposed that methods based on fuzzy sets theory can be applied to deal with the uncertainties in the decision-making on the stream water quality, keeping the importance of uncertainty handling in the water quality assessment and versatility of the fuzzy set theory in the decision-making in the imprecise environment. In this project, we propose the fuzzy set theory for decision-making in the assessment of physico-chemical quality of Nethravathi River of Dakshina Kannada, Karnataka.

Keywords: Fuzzy logic; Membership ; Linguistic variable; Fuzzification