URBANISATION AND IRRIGATION WATER USE

Abstract

In accomplishing overall development projects within a metropolitan area, the existence of irrigation system which is prescribed as a historical inheritance cannot be ignored. Water requirement for new uses other than agriculture caused by rapid urbanisation is confronting a deep-rooted opposition in getting water from the existing irrigation system. This means that it is not only difficult to adjust technically, but also related closely to the complicated socioeconomic aspects of the farming people. This paper intends to study how remarkable changes have been taking place in the existing irrigation system through the impact of urbanisation, taking two areas located within the Hiroshima Metropolitan area. One is the area of the Yagi irrigation system, water of which supplied from the Ota River and the other is an area located downstream from Haji Dam on the Eno River. Consideration was rendered based on a field survey on these two areas with the following results. In the area of the Yagi irrigation system which is undergoing rapid urbanisation, the agricultural function of irrigation is gradually breaking down, starting from the negotiation with the authorities for the possible use of water than agriculture to the use for urban purposes as well as converting rice-fields to urban land. The fact that water use for agriculture is gradually reducing is explained by the attitude of farmers toward urbanisation. They possess their fragmented fields and want to maintain some of them as rice-fields for a long time in small patches in the urbanized land, depending upon part-time farming on one side, and they cultivate crops on their fields expecting only higher land prices. Converting rice-fields to housing and factory sites has the direct and most important relation to the irrigation system. Areal reduction of rice-fields does necessarily cause a decrease in the total amount of irrigation water. As a result of this, the maintenance cost of irrigation system, for which tax is collected by acreage of rice-field, decreases on one side and the expansion of housing and factory sites increases water pallution on the other. Maintenance of the irrigation system has become very difficult. It will be expected that irrigation canals will be used as drains or sewages in the urbanized area in due course. Conversion of irrigation canals to drains is likely to give rise ill drainage in the downstream area on account of the irrigation facilities do not fit draining function. It is important to examine such a problem from the standpoint of city planning. In the area downstream from the Haji Dam located on a fringe of the urbanized area, new requirement for water use has come into being between agricultural and urban uses. As the urbanisation of Hiroshima expanded to a great extent and the increasing demand for water is not satisfied by the supply of stream water of the Ota River, another water resource must be exploited for future water supply, and the Eno River, a different river system, has come into the scene. There developed a traditional water right by which customary irrigation methods are practiced in this area ineffectively. This is a hindrance for the creation of a higher productive organisation. Accordingly, it is necessary to keep it in mind that a new order in the distribution of water is to be created by means of readjustment of water uses in a large area such as a metropolitan area, assuming that the basic conditions in which “betterment of agricultural basement” and “the integrated use of water between agricultural and urban uses” are inevitable.