The Wells in the Central Section of the Nasuno-Basin : A Problem of the Regional Division (2)

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Within the central section of the Nasuno-basin which is discussed in the present paper, seven subsections A, B, C, D, E, F and G are established on the basis of the most important characteristics of the wells, i.e. the depth of the wells, the depth of the water table and the thickness of the water in the wells. The regional divisions are carried out in exactly the same way as in paper (1), taking the general relationship y=x-c into consideration. Although two observations, i.e. those surveyed on Jul.23 and on Sept.2, 1963, are analysed equally in the present paper, the same series of subsections is recognized in connection with those different surveys. Besides, considerable similarities are found between the present series of subsections and the series established in paper (1) on the basis of the observation made on Oct.1, 1950. The most noticeable difference, however, is that in the present paper F is newly delimited as a subsection which is situated between C and G and which exhibits a striking contrast with these subsections, regarding those afore-mentioned basic characteristics of the wells. In spite of this and other minor differences, the similarity as a whole between the regional division in the present paper and the division in paper (1), which divisions are practised on the basis of the different surveys carried out on the different dates, may reasonably suggest the existence of some intimate relationships between these regional divisions and the systems of the ground water. Investigations into this point will be pursued in the near future in connection with the fluctuation of the water table. As far as the present paper is concerned, however, the most important facts regarding the regional differentiations of the seven subsections which are classified here into three categories viewed from the type of regions, are summarized as follows. (1) A is the smallest among the subsections concerning those basic characteristics of the wells and is recognized as typical of the homogeneous region, i.e. the region in which those characteristics are confined within certain ranges of small extent. This subsection which is situated below the upper limit of the springs, covers the southern-most part of the central section and forms perhaps the main oldest reclaimed area within the section concerned. (2) The series of contiguous subsections C, D, E, F and G, all of which extend from the southeastern to the northwestern part of the central section toward the apex area of the fan, is strikingly contrasted with A considered from the regional viewpoint. First of all, the depth of the wells as well as the depth of the water table in these subsections are, as a rule, far greater as compared with those depths in A. The most conspicuous characteristics common to these subsections, however, are the general growing tendency of those depths toward the apex area of the fan and, as a consequence, the wide ranges between the upper and the lower limits of those depths except in newly established F. Therefore, C, D, E and G which form characteristic heterogeneous regions in opposition to the homogeneous region A, are typical of the transition region viewed from another angle, as far as the depth of the wells and the depth of the water table are concerned. The thickness of the water which remains similar among C, E and G on the one hand and between D and F on the other is considerably larger in the former group as compared with the latter. Within the series C, D, E, F and G the delimitation of the subsections is carried out in connection with the thickness of the water. The boundary line between each contiguous subsection is therefore drawn where a sharp change in the thickness of the water occurs. Only between C and E the boundary line is established as in paper (1). (3) Between A on the one side and the series of subsections C, D, E, F and G on the other, a region of a different type is recognized, i.e. a long and curved belt of B. This subsection is almost exactly determined as forming a distribution area of those depths of the wells, which change sharply within a short distance from the upper limit of the depth in A to the lower limit of the depth in the series C, D, E, F and G. Therefore, B, which is situated between A and the series, is not only typical of the transition region, but also typical of the sudden transition belt. The thickness of the water in B, which is limited within a certain range of small extent and which remains between those thicknesses in C, E and G on the one hand and those in D and F on the other, forms one of the bases upon which B is delimited from the series in question. Between this thickness in B and the thickness in A which is decisively smaller than the former, a sharp contrast is recognized especially along the northeastern boundary between these two subsections A and B. The northern limit of the springs occurs, as a general rule, through the area of B where not a few old settlements before the Meiji era were established especially beyond the northern boundary of A. The present author has to acknowledge his indebtedness to the Scientific Research Grant of the Ministry of Education for the year 1964. He is also deeply indebted to the Kanto Regional Office (Kanto Nosei-Kyoku) of the Ministry of Agriculture and Forestry for the ample facilities afforded to him to make use of the data analysed in the course of this study. His cordial thanks are also due to Miss Setsuko Okazaki for her 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 (2)

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