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Recently, the frequency of severe torrential rain storms has been continuously increasing as an effect of abnormal climate. Annual flood damages and water quality degradation continuously worsen despite the imposition of flood and water quality managements. Hence, suitable analyses should be made to mitigate future flood damages and water quality degradation in riverine systems. In this study, two major analyses were done: analysis on the variation of the flood frequency and water quality. The principal method used to analyze variation of the flood frequency is through the application of flood-frequency analysis in time series on flood discharges. For the flood-frequency analysis, the stream flow data used were gathered from 25 gauging stations located in Geum River Basin. The Log Pearson Type III distribution was used to determine the probability of the flood discharges. The annual maximum series of the flood discharge data from stations was divided into two parts: the historical data and the present data. Flood-frequency analysis was performed to determine the influence of the effects of abnormal climate to the flood discharge in Bugil and Seokhwa stations. For the second part of this study, the water quality data such as BOD, COD, and SS for 24 years were also collected for the analysis of variation patterns of water quality induced by abnormal climate. This study showed that the flood frequency by flood-frequency analysis using the present data was higher compared with the historical data. Further findings showed that, both COD and SS consistently increase while BOD decreases in a yearly basis. [ABSTRACT FROM AUTHOR]