VARIATIONS OF STREAMFLOW DISCHARGE AND HYDROLOGICAL MAPPING OF THE TONE RIVER SYSTEM

Abstract

The Tone river system has long been utilized as one of the major water resources for Kanto district, but the situation becomes serious due to human impact on the river system. Recently. the utility value of the river system is enhanced with the demands of water supply which have an increasing tendency year by year. In order to estimate the utility value at present and in future, the changes of river regime of the Tone river system should be clarified. The purpose of this paper is to show the changes of the river regime and to delineate a hydrological map. The data used in this paper are the annual total discharge, the annual mean discharge, the minimum discharge, the maximum discharge, the monthly discharge, the annual rainfall, and the monthly rainfall from 1938 to 1977; these data were obtained by the River Bureau, the Ministry of Construction (The Civil Engineering Bureau, the Ministry of Interior was in charge before the World War II). The mean values of these data were calculated in every ten years and during forty years since 1938 (Tables 1 and 2). The time variations of run-off, run-off percentage, coefficient of river regime, and loss were calculated (Table 3). The thirty-two discharge and thirteen rainfall gauging stations were selected to present the river regime. The changes of river flows of the major rivers were shown in Figures 1 through 7. Figure 8 shows the hydrological map of the regime with the annual total discharge, the non-dimensional hydrograph, the run-off percentage, and coefficient of river regime. The results of this work are summarized as follows: 1. The Tone river system can be hydrologically divided into two groups except the Katashina River and the upper reach of the Tone River which are rather unique in their flow regime. The one group embraces the Kokai, the Kinu and the Omoi Rivers and the other includes the Watarase, the Agatsuma, the Karasu, the Usui, and the Kabura Rivers. 2. Although the main stream of the Tone River has presented the various changes during the last forty years, the others have fairly constant values. 3. The hydrological map cannot perfectly have a function as a general one because of the difficulties of making techniques. 4. It is recommended that we had better use various kinds of colors in expressing the variations of river flows.