Application of Improved Entropy-Weight TOPSIS Model Based on Gray Correlation Method (EWTG) to River Outfall Water Quality Evaluation

River outfall water quality evaluation is an important issue for the local government in water environmental protection and management decision. The entropy-weight TOPSIS model was redesigned basing on grey correlation method (EWTG) in this paper and make a water quality evaluation for 22 river outfalls with 4 monitoring indicators of Duliujian River in Tianjin. The informative weighting was introduced to reduce errors caused of subjective weighting. Then the grey relativity of ideal distances solution and non-ideal distances solution distance and various index was calculated. Finally, the water quality was evaluated the by the relative closeness. Comprehensive closeness degree and geometric similarity relation were comprehensively considered in this model. By comparing entropy-weight TOPSIS model and comprehensive water quality index method, this model with good reliability and stability could be used to river outfalls water environment quality. Evaluating river outfalls water quality by this model to offer a technological support for environmental remediation.