Abstract: The middle route of South-to-North Water Diversion Project (SNWDP) is an important water source for Beijing,Tianjin,Hebei Province and Henan Province.Water quality safety is of essential importance for the stable operation and optimal management of the project.The changes of nine water quality indicators in 25 cross-sections of the main canal of the middle route of SNWDP were analyzed to investigate the water quality condition and spatiotemporal variation characteristics of the main canal.The major water quality indicators were identified,and the similarity of water quality changes among cross sections was discriminated via principal component analysis and cluster analysis.Evaluation and zoning of water quality was also carried out to provide decision-making reference and optimization suggestions for water quality protection and management.The nine water quality indicators were reduced to four by the principal component analysis,and the first four principal components could reflect 80.23% of the original environmental information,of which the degree of oxygen consumption and acidification trend should be paid special attentions.Moreover,the main canal was divided into four segments by cluster analysis.By comparing the differences in water quality indicators among each segment,the key water quality indicators in each segment were identified.The research findings offer a theoretical basis for the protection and management of water quality in the middle route of South-to-North Water Diversion Project.

Key words: middle route of South-to-North Water Diversion Project, principal component analysis, cluster analysis, categories of water quality indexes, spatiotemporal variation characteritics