Fuzzy comprehensive assessment on spatio-temporal variations of water quality of a small catchment
模糊综合评价在小流域河道水质时空变化研究中的应用

Many approaches have been developed to assess water quality of rivers, and fuzzy comprehensive assessment (FCA) plays an important role. It is capable of tackling the problems caused by the diversity of assessment indexes and the fuzzy characteristics of the degree of water pollution. According to the principles of FCA, analysis of water quality from upstream to downstream on a time horizon can be performed in several steps. The fuzzy assessment standard and the weights of the water quality index should first be determined, and the fuzzy sets for each single time point should then be calculated. Finally, the spatio-temporal variations can be obtained through time weighting. The Caojialu catchment of the Miyun reservoir basin was selected as a case study. The water quality parameters (TOC, TP, TN, etc.) of 10 cross-sections were measured for 5 consecutive days during the wet season of 2009. It was found that the concentration of some parameters increased from upstream to downstream, while others decreased. Therefore, an improved FCA method was applied to further analyze the data. The results showed that the water quality tended to become worse from upstream to downstream, in particular the changes were more obvious in the reaches that flow through residential areas.