Abstract
The water quality data of the Sagami River at 12 stations from April 1976 to March 1980 were analyzed by the Principle Component Analysis (PCA) method.
Water Quality Index (WQI), which was proposed in this paper as an evaluation of the pollution level as caused by human activities, was reached as follows. First, the test of normal distribution was carried out for 10 water quality items and the most appropriate tarnsformation type that brought each item closer to normal distribution was selected among the three types, i.e., original data, square root and logarithm. Next, PCA was performed by using the transformed data. The first component of PCA with 10 items was ascribed to the pollution caused by human activities. Then the 6 items (DO, BOD, COD, PO4-P, NH4-N and NO2-N) which showed high contribution to the first component were selected for the further analysis. The equation derived from the first component of PCA with 6 items was used to evaluate WQI.
WQI at 11 stations displayed little or no yearly change except in 1978. In 9 stations, WQI at night was found to be worse than daytime WQI. Such characteristics could not be obtained by analyzing only BOD data.
The relationship of WQI with natural and social factors in the tributary basins was also discussed. The results showed that there was a high correlation between WQI and flow rate, basin area and population density factors.
