Techniques of Real-Time Flood Forecasting and Low Flow Prediction for Reservoir Operation

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Main results obtained in this study are as follows :1. A questionnaire on actual circumstances of reservoir operation was carried out in cooperation with government agencies. It is outlined by summarizing the information on 201 reservoirs with catchment over 50km^2 that real-time forecasting up to 3 hours ahead is of critical importance for flood flow, and that runoff models are used for flood forecasting in about half of the reservoirs, but the filtering techniques are rarely used in actual reservoir operation.2. In order to examine the performance of Long-and Short-Term Runoff model (LST-II) and Tank model used in real-time flood forecasting, both runoff models were applied to the data of 18 years (1979-1996) observed in the Kuroki Dam basin. It is shown that observed hydrographs both in long-term runoff and flood runoff were simulated with good accuracy by both runoff models.3. Such filtering techniques as extended Kalman filter, statistical linearization techniques and back calculation method were applied to real-time flood forecasting with lead time of 1 and/or 3 hours in the Kuroki Dam basin. The results of 19 floods in the basin demonstrate that more accurate flood prediction is attained by adopting the filtering techniques, and that the accuracy evaluated by relative error of predicted discharge by each technique is almost same.4. The performance of several methods for rainfall prediction in real-time flood forecasting was compared by using flood data in the Kuroki Dam basin. It is shown that the simplest method, in which future rainfall are assumed to be constant with the present intensity, gives best results, and that setting the limitations of values of coefficients is necessary for applysing the AR (auto-regressive) method.