Characterization of Water Quality in Yodo River

In order to elucidate the characteristics of water quality fluctuation of Yodo river, regression analysis was carried out by using the daily data which were obtained by the measurement with 20 items at TOYOSATO Station. The concentration of measured substance, except BOD and ammonium nitrogen, was fitted to the following equation C=a⋅ Qb, in which C and Q are concentration and flow rate, respectively, and a, b are constant. The concentrations of inorganic dissolved substance and dissolved organic carbon are decreasing with an increasing flow rate. The concentration of suspended substance is increasing with increasing flow rate. The concentrations of organic pollutants, nitrogen compounds, potassium ion and magnesium ion are decreasing with an increasing flow rate below ordinary flow rate, but those concentrations increase with an increasing flow rate above ninety-five-day flow rate (350m3/sec) . This is because of wash loading effect by change of flow rate and rain-fall. The concentrations of BOD and ammonium nitrogen was not related to flow rate, and it was thought because of the effect of water temperature. Those have been classified into 3 categories.