The study looked at the water quality of surface runoff and groundwater runoff in the Yodo River and Asahi River basins using a numerical filter. They found that surface runoff and groundwater runoff have different water quality, with changes in concentration varying with river discharges. Groundwater runoff quality often changes clockwise with river discharges. Differences in COD and SS concentrations were linked to population and industrial activities. Lower SS concentrations were seen in surface runoff, while COD concentrations were higher in groundwater runoff. Nutrients and chlorine ion levels were also examined.