The Wells in the Central Section of the Nasuno-Basin : A Problem of the Regional Division

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The central section of the Nasuno-basin, which is treated in the present paper, is divided on the basis of the depth of the wells, the depth of the water table and the thickness of the water in the wells into six subsections A, B, C, D, E and F (Figs.1, 2 and 3), in a systematic way, taking the general relationship y=x-c into consideration, which is found with regard to these subsections, where y and x means respectively the depth of the water table and the depth of the wells while c signifies a value which exists between the upper and the lower limits of the thickness of the water, both being characteristic of the respective subsection. These six subsections are compared and contrasted, in connection with the upper and the lower limits regarding x, y and z as shown in Table 1. The isopleths which express the distribution of the depth of the wells (Fig.4) and the depth of the water table (Fig.6), run in a similar way, nearly eastwest in D, E and C and turn abruptly to the south in F. This represents the increasing tendency of both values from south to north or from A through B to the northern portion of D, E and C on the one hand, and from southeast to northwest or from A through B to the northwestern portion of F, on the other. A similarity rather than an identity, however, is found between these isopleths, because of c which is different among the six subsections ; the most conspicuous disimilarity is recognized in connection with C where the isopleths are pushed far north as compared with those showing the same depth of the water table in D, E and F, leaving a wide area of small depth from A through B to C (Fig.6). Such small depth of the water table during the high water season, as well as the large thickness of the water, both characteristic of C (Tab.1) may partly be due to the subdrainages of the rivers Sabi and Kuma. Regarding the distribution of the thickness of the water, which ranges within a certain limit proper to the respective subsection (Tab.1), rapid transitions are pointed out between D and E, on the one hand, and between C and F on the other (Fig.5). The subsection B which occupies a sharp transition belt with regard to the depth of the wells as well as the thickness of the water (Figs.4 and 5) and in which the water table fluctuates to a certain extent larger compared to A, resulting consequently in a conspicuously shallow water level during the high water season (Fig.6), coincides to a considerable degree with the upper limit of the springs (Fig.3). These facts which are important in connection with the relationship between the ground water and the agricultural land use, especially from the regional point of view, may be studied later. The present author has to acknowledge his indebtedness to the Scientific Research Grant of the Ministry of Education for the years 1962 and 1963 and also to acknowledge the courtesy of the Kanto Regional Office (Kanto Nosei-Kyoku) of the Ministry of Agriculture and Forestry in affording facilities to make use of the data analysed in the course of this study. The author also wishes to express his sincere thanks to Mr. Takanori Hara for his kind assistance extended to him in analysing the data.
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松井勇
Department Of Geography Faculty Of Literature And Education Ochanomizu University

The Wells in the Central Section of the Nasuno-Basin : A Problem of the Regional Division

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