Unit load method has been widely used in evaluation of pollutant load from watershed to lake or inner bay. However this method has several issues for accurate evaluation of pollutant load. In this study, we present a new approach for evaluation of unit load averaged over infiltration basin under low-flow conditions using longitudinal variations of pollutant load and point source using GIS. For this purpose, we conducted water sampling and discharge measurement in Takasaki River, flowing into Lake Inba-numa. The results indicate that unit load averaged over infiltration basin of Takasaki River in spring and summer was quite lower than that in autumn and winter. The tendency of the seasonal variations of unit load is closely related to land use of plowed field.
