Water quality investigation in the Hawkesbury-Nepean River in Sydney using principal component analysis

![CDATA[The Hawkesbury-Nepean River System (HNRS) is an icon of Australia’s largest city Sydney. Although there are a number of dams and in-stream structures throughout the river system, the HNRS is considered to be an unregulated river. Since European settlement, the HNRS has been used as a primary water source to meet the drinking water needs for over 80% of Sydney’s population. The fact that it is located in the peri-urban areas dictates that it receive pollutants from a number of sewage treatment plants, located within the catchment, and the storm water runoff from agricultural and urban lands. Sydney Catchment Authority regularly monitors the water quality of the HNRS which generates a large three dimensional (different sampling stations and different parameters over time) data set containing useful information on pollutant build up and washoff on/from this river system. In this study, factor analysis was used to identify the most significant water quality monitoring station(s). It was found that the three principal components explained more than 90% of the total variance in the data set. Moreover, this study showed that the dimensionality of the water quality parameters can be reduced to eight principal components which explained more than 70% of the total variance. Information obtained in this study can be used to design an optimal sampling strategy, which could reduce the number of sampling stations in the river system. However, further study is needed to confirm this initial finding.]]