Attentions are being paid recently to the relationship between tidal movement of water and water quality change in estuaries. Water quality data collected in the near-estuary of the River Han were analyzed by correlation between water quality factors determined by pattern analysis and major component analysis, and the phenomenology of water quality change mechanisms was studied.
No significant difference in water quality pattern was observed between different directions of flow or different water depth in the River Han. In upstream to midstream or in tributaries, major portion of water quality change may be described by decomposing the changes in organic pollutants represented by BOD or COD. In downstream and the estuary, however changes in inorganic nutrients appear to be more important than the changes in BOD or COD.

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The typical sedimentation index of activated sludge is SVI (Mohlman index). It is true that this index has been used for a long in spite of its application restriction. For this reason, some indices are proposed to replace SVI.
In this study these indices, including SVI, have been reconsidered on the basis of the results of our experiments. At the same time an attempt has been made to grasp them accurately. Our reconsideration points out that SVI is an approach on the basis of monopunctual evaluation. We have made an analysis of SVI which is different from what has been made so far. Our analysis shows that standard SVI is a monomial approximation of SV₃₀-MLSS curve. In order to replace SVI we propose to use linearized SVI as sedimentation index for normal operation and as a more exact index, to use LSVI, β or LSVI, β, MLSS_1.0^*
Finally it must be said that we have developed a system to measure the sedimentation indices automatically with the aid of the microcomputer and optical instruments.

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