Study on Effective Utilization of Hydrological Information in Management of Flood and Low Flow

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1. The concentration time of river basins subject to the unsteady rainfall was analytically derived from the kinematic wave theory, and the effect of variation of rainfall intensity in time on the concentration time and the peak discharge was quantitatively evaluated. Based on this theoretical consideration, the method to estimate the concentration time from observed hyetographs and hydrographs was proposed. As a result of applying this method to the observed data, the significant and unified relations of the concentration time to the rainfall intensity and to the topographical elements of the basin were definitely found out for such basins that the concentration time at the mountain slopes of is dominant over the total concentration time, while the one at the river channels is much short of the one at the slopes.2. The three-dimensional ultrasonic velocity meter was employed to measurement of the flows in a laboratory flume and in river channels. Analyses of the observed data yielded … More the hydraulic properties of flows, namely, the mean velocity, intensity of turbulence, Reynolds stress and energy spectrum in each direction, and revealed some differences between the properties for the laboratory flume and those for river channels. It has been confirmed that the ultrasonic velocity meter used in the present study operates stably during several hours of the field observation and therefore it has the practical usability to measurement of three-dimensional flows in the river channels.3. The procedures to evaluate the value of information on future inflows in operation of a reservoir for water utilizations were presented. Numerical simulations of reservoir operation showed that it is of most value to obtain the advanced information on the times when a drought period begins and ends, although the worth of these times sharply decreases as the errors in information increase. A method was also proposed to utilize such information on future streamflow sequences for real-time operation of a reservoir. Less