ON THE LANDSCAPE OF “SHIMABATA” (ISLAND-LIKE UPLAND FIELDS) IN THE KUJUKURI COASTAL PLAIN—WITH SPECIAL REFERENCE TO THE RECLAIMED LAND OF CHINKAI LAGOON—

Abstract

The Kujukuri Coastal Plain located in Chiba Prefecture is a narrow elevated coastal plain stretching approximately 60 kilometers in length and 7_??_9 kilometers in width. Topography of this plain consists of sandy beach ridges (or sand banks) running in parallel to the coastline and marshy lowlands lying between these parallel ridges. Until recent it was said that, largely in conformity with these topographical features, the sandy beach ridges were used for settlements, upland fields, etc., while the marshy lowlands were used for paddy cultivation, creating such a characteristic land use of this coastal plain. On the basis of 1 : 10, 000_??_1: 3, 000 large-scale maps, the present author carried out an investigation into the land use of this plain, and came to the conclusion that this view hitherto held as general knowledge was erroneous. In other words, the view that the sandy beach ridges are used by upland fields or that there are no paddy fields there is a fallacy. As a matter of fact, most of the sandy beach ridges include many island-like upland fields or “shimabata”, therefore even here, there are many paddy fields. Stating it in other terms, numerous paddy fields are found not only in the marshy lowlands but also in the sandy beach ridges. As clearly presented by the author's survey on the distribution of “shimabata” in Japan (see Geographical Review of Japan, Vol. 41, No. 4, 1968), the Kujukuri Coastal Plain is an area noted for the distribution of “shimabata” landscape. The main purpose of the present paper is to clarify the reasons for the large-scale development of this type of land-scape. Lagoons in the marshy lowlands and a few irrigation reservoirs built in dissected valleys of the diluvial uplands bordering the western boundary of the plain have long been used for paddy cultivation. However, paddy fields that could be irrigated by these sources amount to only a small proportion of the total paddy fields in the marshy lowlands, and so the majority were rainfed ones. Even if the sandy beach ridges were only slightly higher than the marshy lowlands by 50 centimeters or so, it was impossible to make any paddy fields unless the elevation of the ground surface was lowered. In order to expand paddy fields into the sandy beach ridges, the farmers dug the lower parts of the ridges. Cultivation was practiced on piled up spots, while in the dug places, paddy fields were realized. The result was the island-like upland field landscape where upland fields and paddy fields are found alternately. Groundwater table is generally high in the Kujukuri Coastal Plain, and so if rain falls at suitable intervals, rice can be grown well in rainfed paddy fields. The reclaimed land of Chinkai Lagoon is located in the northern part of the Kujukuri Coastal Plain. This reclaimed land was created in the early years of the Tokugawa Period. This is an area always suffering from shortage of irrigation water. There is a wide distribu-tion of “shimabata” on this reclaimed lands, too. Blank parts enclosed by dotted lines in Fig. 2 indicate places where “shimabata” are found. The distribution pattern corresponds to the shallow lagoon bottoms that were reclaimed. Two sample areas were taken from the distribution areas of “shimabata” in Figs. 3 and 4. The black parts are “shimabata”, while blank parts show paddy fields. A complicated pattern shown in Fig. 3 is surprising. Difference in elevation between “shimabata” and paddy fields is, in general, 30 to 40 centi-meters. Slightly higher lands (about 50 cm) in this reclaimed land, the ground water table is relatively low. In order to have it closer to the groundwater table, earth should have been dug to make paddy fields. The result is the landscape of “shimabata”.Figure. 4 shows the narrow “shimabata” made alternately with narrow paddy fields.