Abstract
The Yodo River, which has a large discharge area, is a source of tap water for fourteen million citizens in the Kinki area. It is also an inflow river supplying the largest pollutant load into Osaka Bay. The flow of the Yodo River, which has the Lake Biwa basin and seven dams in its upper reaches, its flow is usually stable and large water quality changes occur only during flooding stages. During our highly frequent routine observation (once every three days) , eleven events of the ordinary flooding in 2005-2006 and one of the superflooding due to the 1318 typhoon were observed in our past observation period. For superflooding the highest concentrations of T-COD, TOC, and SS, and the largest loadings of all pollutants were observed during the observation period of 1995-2013. The results may be useful reference data for automation operation systems in water supply plants and for the estimation of the impact of inflow pollutants on Osaka Bay. The shares of loads, discharged during the superflooding stage to the annual total load in 2013 were estimated. The differences between the regression equations of total loads of pollutant for the six largest flooding events, included the superflooding event, and all twelve events were clarified. Annual total loads of pollutants were estimated using L-Q equations on the basis of the highly frequent observations in 2013 and ΣL-ΣQ equations for the six flooding events. The total loads in the Yodo River could be estimated with high precision using by the regression equations.
