Irrigation Systems in Japan I. Introduction Rice Cultivation Has
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Geographical Review of Japan Vol. 60 (Ser. B), No. 1, 41-65, 1987 Irrigation Systems in Japan Aklra TABAYASHI* This paper portrays the distribution pattern of irrigation systems in Japan and then analyzes the pattern with respect to elements of the natural environment and of the irrigation development process. Irrigation systems in Japan are classified into (1) river, (2) pond, (3) lake, (4) ground water, (5) torrent, and (6) other systems. River irrigation systems dominate overwhelmingly and occur widely, but especially in eastern Japan. Pond irrigation systems are important in western Japan, centered on the Inland Sea. Various types of irrigation systems exist together in the Kanto district, and torrent systems are common in mountainous areas. The basic features of irrigation systems in western Japan were formed during the Kofun and Nara periods (300 to 800 A. D.). On the other hand, the main systems in the east were built largely in the Sengoku and Edo periods (1450 to 1867 A. D.). In the large systems, a hierarchical structure of water management coopera tives and water delivery methods that accords with the branchlike network of canals was established in the Edo period (1600 to 1867 AD.). hold economy. Irrigation systems not only I. Introduction influenced rice cultivation but also production of crops other than rice. Farmers' life styles Rice cultivation has long been the core of and cultures were similarly affected by irriga agricultural activities in Japan. The high tion systems. Although rice cultivation is productivity of rice per hectare of fields in a much less important in rural life and the humid and temperate environment has made farming economy today, irrigation systems it possible to support a large population on a play a major role in shaping the structures of small land area. That Japanese rice cultiva Japan's agricultural regions. tion enjoys high yields in comparison with As an agricultural geographical study seek other Asian countries owes also to sophisticated ing to describe and explain spatial variations irrigation systems created by huge labor and in agricultural activity on the earth's surface capital investments for land improvement (GRIGG,1984, pp. 13-18), an analysis of rural works over many centuries (NAGATA,1971, regions from the viewpoint of areal differences pp. 24-33). in irrigation systems has a significant meaning. The evolution of rice producing regions has This paper classifies irrigation systems in been closely related to progress in the develop Japan, and describes and analyzes the dis ment of irrigation systems, for irrigation tribution patterns of the main types of systems. systems have played an important role in It also examines the development processes supporting successful rice production in Japan. of the main types of irrigation systems. Although about 86 percent of all farm house holds are part time farmers today, and farm II. Main types of irrigation systems ing itself is not an important source of income in Japan. for them, until the 1950s most farm households 1. Classification of irrigation systems lived on farming, especially rice cultivation. In contrast to crops grown on dry fields such Geographers have described and explained as peas, beans, wheat, millet, barley and sweet regional characteristics of irrigation systems in potatoes, the higher monetary value of rice Japan by examining such features of the per hectare was very important for the house systems as their sources of water, their water * Institute of Geoscience , The University of Tsukuba, Ibaraki 305, Japan. 42 A. TABAYASHI carrying and water division structures, their divided into ones with several ponds and ones customary water use practices, their water with a single pond. Pumping irrigation sys management organizations, and their land tems encompassed those using groundwater scape locations. However, in Japan the type and those using surface water. Creek and of water source often strongly influences other ganat systems belonged to the category of features of an irrigation system (TAMAKIand other irrigation systems. HATATA,1974, pp. 228-229). Therefore, the Geographers YAMAGIWA(1928), INOKI(1935), present study focuses attention on water MATSUI(1964) and others discussed river, sources, and irrigation systems are classified pond, groundwater and spring irrigation sys on the basis of their water sources. Terms tems. Books recently published by TAKEUCHI such as river irrigation, pond irrigation and (1980, 1984) describe pond, groundwater,lake, groundwater irrigation are common in the and river irrigation systems. They also ex Japanese literature because they connote more amine rain-fed terraced paddy fields and creek information than simply the source of water. irrigation systems in the Saga plain of Kyushu For example, groundwater irrigation is almost along the Ariake Sea. HORIUCHI(1983) has always small scale because the area served by been engaged in research on various types of a well is small. As such, groundwater irriga irrigation systems in the Kinki district and tion systems are managed by single farmers in particular has analyzed river, pond and or small groups of farmers, and water manage groundwater systems. In addition, he has ment procedures are simple. On the other described features of a system pumping water hand, many river irrigation systems are large. from Lake Biwa to nearby paddy fields. ARAI Their main canals gradually decrease in size (1986) classified paddy field irrigation systems as they are tapped by branch canals. A part into river, pond, vertical well and horizontal of a branch canal may serve most or all the well systems. land of an entire village. Thus, a single river The present study classifies irrigation systems irrigation system is commonly managed along in Japan into categories called (1) river, (2) parts of its branch canals by villages, along pond, (3) lake, (4) groundwater, (5) torrent, branch canals or parts of its main canal by and (6) other (Table 1). River irrigation groups of villages, and along its main canal systems include subtypes on alluvial fans and at its water source by a municipality. where water flows by gravity, and on deltas Within such a large irrigation system, all where gravity irrigation is impossible. Creek farmers have an interest not only in the pattern irrigation systems are essentially a variation of water flow in their local branch canal but of the delta subtype. In addition, river also in the main canal and the water source. systems are subdivided according to the size Water management procedures at the system of rivers, small, medium or large, from which or district level may be extremely complex they take water. because of competition among subdistricts Pond irrigation systems encompass two sub (TAMAKI,1983). types, parent-child pond systems in which a The Department of Agricultural Land of the large pond distributes water to smaller ponds, Ministry of Agriculture and Forestry in 1960 and single pond systems. Water in both sub classified irrigation systems into river, pond types flows by gravity. Traditionally, lake and creek systems, and rain-fed paddy fields. irrigation systems involved small scale water NAGATAet al. (1982) discussed recent agricul tapping using such devices as buckets handled tural changes in areas irrigated by rivers, by two persons, dragon pumps and foot pro ponds and creeks. HIRASHIMA(1984) divided pelled water wheels to irrigate fields within irrigation systems into categories called river, just a few meters of the lake. However, large pond, pumping and other. He further sub scale pumping stations that have appeared divided river irrigation systems into those mainly since the 1920s enable water to be with a diversion dam and reservoir on a river lifted and then transported several kilometers and those diverting water directly from the upcountry from a lake. The groundwater river. Pond irrigation systems were sub category of irrigation systems has two sub Irrigation Systems in Japan 43 Table. 1 Types of irrigation systems in Japan Table. 2 Hectarage of paddy fields by main sources of irrigation water (1000 hectares) * included in others Source: K. NAGATA,1971; Nogyo suiri kenkyukai,1980 types, an ordinary vertical well and a hori are low enough to reach groundwater level and zontal well. Formerly, sweep-well buckets rain fed paddy fields. and windmills were used for pumping water Table 2 shows the hectarages of paddy from vertical wells, but they were replaced fi elds in Japan by main source of irrigation by motorized pumps mostly after world War water in the years 1907, 1942, 1955, and 1977. II. The horizontal well called manbo is a All irrigation types mentioned above are not long tunnel-like excavation on a natural in represented in the table owing to lack of data. cline in which ground water is collected for The figures indicate that about 75 percent irrigation purposes. Torrent irrigation sys of all paddy fields now depend on river irriga tems utilize small mountain streams as sources tion, followed by pond irrigation which sup of water. Terraced paddy fields on steep plies water for about 14 percent of paddy slopes may be supplied with water by such fi elds. Groundwater and torrent irrigation systems. In a sense, torrent systems are a systems together serve about one percent. subtype of river systems. However, they The total area of irrigated land has grown by are considered a separate category here be about 20 percent and the area of river irrigated cause special facilities and methods are required fi elds has increased by about 35 percent in to catch the water torrents and direct them to this century. In 1970, over 60 percent of all fi elds. The category of other irrigation systems villages were served mainly by river irrigation includes dug down paddy fields whose surfaces systems, 15 percent by ponds, and 10 percent 44 A. TABAYASHI Table. 3 Number of villages by main source of irrigation water Source: Agricultural Census, 1955, 1970 by torrent systems (Table 3).