Abstract
To clarify the mechanism of water quality change in the estuary of the Asahi River and Kojima Bay, Okayama Prefecture, we analyzed the concentrations of Cl ion, SS and COD (Mn) and discussed the relationship between the surface concentrations and vertically averaged ones.
The conclusions may be summarized as follows :
1. Judging from the distribution of Cl ion concentrations, the Asahi River estuary is of a partly mixed type within the range of freshwater inflow from 0 to 50 m3 /s.
2. If we compare the daily or half daily time average of surface and vertically averaged concentrations, the curves of their longitudinal distrbution are very similar. However, we do not always find a correlation between surface and vertical concentrations at the same spot at the same time.
3. As for the standard deviations and the coefficients of variation, those of surface concentrations are greater than those of the vertically averaged.
4. As mentioned above, the surface water quality of the Asahi River estuay varies more than the vertically averaged qualities. So to obtain the longitodinal distribution of water quality level from surface water quality, samples for analysis must be taken sufficient times a tidal cycle.
