Upland Field Irrigation Made Available by Three Irrigation Projects in Aichi Prefecture

Abstract

This paper deals with upland field irrigation in Aichi Prefecture. In 1975, Aichi Prefecture had the highest ratio of upland fields equipped with irrigation facilities to total available upland field area. This high ratio was accomplished due to large-scale projects such as the Aichi, Nobi, and Toyokawa irrigation canal projects.At present, the degree to which the upland field irrigation sheme is successful and to which the upland field irrigation facilities are useful vary widely among the areas where the three canals are intended to benefit. For example, in the region served by the Aichi Canal (Aichi Canal Area = Aichi C. A.), the scheme's size has been reduced and, for the most part, the upland field irrigation facilities have been abandoned. The project scheme in the Nobi C.A. has been similarly unsuccessful, and, furthermore, upland field irrigation facilities lie idle. But, in the Toyokawa C.A., the scheme has been greatly expanded and maximum use is being made through the scheme's facilities.A study conducted to find the causes of such big differences in success and in usefulness clarified the following points : 1. The reaction of farmers toward the upland field irrigation project can be understood by seeing the extent they promote the project and make use of the upland field irrigation facilities after they are completed. The main factor influencing whether or not the farmers will use the irrigation facilities is based on their previous experience with upland field irrigation using small-scale facilities, not their intentions to promote upland field irrigation themselves.2. In the Aichi C.A., land has not been consolidated and, to make things worse, the surface irrigation facilities were provided with scheduled watering of upland rice. Consequently, the secondary canals and the channels located in the lower stream of the trunk canals are basically non-pressured open type channels, and channels equipped with low-pressure delivery valves are used in both paddy and upland fields. The watering method's uses are, therefore, limited, and the extent to which the upland field irrigation facilities can be used is restricted because the facilities are used jointly both for paddy and for upland fields.In the Nobi and Toyokawa C.A.s, on the other hand, pressurized closed type pipelines, used exclusively for upland field irrigation, are extensively provided. This is especially true in the Toyokawa C.A., where a complete set, consisting of farm pond, pump station, pressure increasing tank and duster, is located in each section of the upland field iriigation system. The system can, therefore, make use of various irrigation methods, depending on whether high or medium pressure delivery valves are in operation.Nevertheless, upland field irrigation facilities and land consolidation alone cannot adequately explain the differences in the extent to which the upland field irrigation facilities have been used in their respective areas. In the Nobi C.A., for example, although land was consolidated and flawless upland field irrigation facilities were made available, the facilities are still lying idle.3. As an example of a regional agricultural management base accepting upland field irrigation in the Aichi C.A., the number of part-time farmers has increased bacause of the accelerated pace of industrialization within the area. As a result, the number of agricultural laborers has noticeably decreased. In the Nobi C.A., the widespread conversion of farmland into housing lots, the widespread abandonment of farming, and the large reduction in farming area and agricultural labor, all indicate the widespread lack of enthusiasm for running farms. As explained above, the agricultural management base in both regions-the Aichi C. A. and the Nobi C.A.-is weak and fragile. Except in a few areas, this results in upland field irrigation facilities are being abandoned and have been left unused.