Study on Synthesizing the Long and Short Terms Runoff Model

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The long short terms runoff model for analyzing both flood and long-term renoff successively is applied to five mountainous watersheds: Eigenji Dam basin of 132km^2, Yubara Dam basin of 255km^2, Yunogo basin of 490km^2, Hisaki basin of 979km^2, and Iwato basin of 1,717km^2.The model has 14 unknown parameters. These parameters are identified for two or three years of data using mathematical optimization technique. the results of simulation agree well with observations of flood and long-term runoff not only for the identification period but also for the residual period of verification.Lag time for simulation of flood runoff is introduced on the basis of theoretical discussion about characteristics of peak runoff in the model. The lag time is suggested to depend upon watershed area and peak discharge for a given flood.A simple technique for real-time prediction of flood runoff is proposed. The technique is shown to be effective for practical purpose.