STUDY OF THE IRRIGATION SYSTEM IN THE KINOKAWA PLAIN

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The Kinokawa Plain spreads gradually below Hashimoto City in Wakayama Prefecture ; it lies delta-shaped ranging about 40 kilometers eastward to westward ; it reaches about 2.5 to 5km in width on the right bank area, but only about 0.5km on its left. Here follows a study of historical geography of the Kinokawa Plain to give some regional characteristics of its irrigation system ; however, this study is stressed about the right bank area. The features of irrigation in the Kinokawa Plain are as follows: 1. The Kinokawa Plain yields the highest rice crop in Wakayama Prefecture. The lower parts along the banks of the Kinokawa were cultivated into the paddy fields by using brooks and ponds in the early days, but later around the middle of the Tokugawa Era, when of the Kinokawa began to be used for irrigation, there were also more and more paddy fields developed in the terraced area. Thus, the paddy fields now stretch long and narrow from east to west along the Kinokawa, the lower being applied to river-irrigation and the upper to pond-irrigation. 2. The Kinokawa is the second greatest river in Wakayama Prefecture. The water of the Kinokawa began to be utilized for transportation and irrigation in early days. Dams were built for utilization of the water in agriculture and the long flumes running from them supply the water of the Kinokawa from upstream to downstream or from the upper to the lower. Long flumes and a wide area of irrigated land are characteristic of the irrigation of the terraced land ; the Kinokawa is its typical example. The earliest water-supply by dam was afforded when ‘Mlyal Dam’ was constructed down-stream of the Kinokawa from 1346 to 1361. It irrigated the neighborhood of Wakayama City. After that, ‘Arai Dam’ was built in 1667, ‘Fujisaki Dam’ in 1696, ‘Rokko Dam’ in 1697, ‘Oda Dam’ in 1707 and, thus, ten of them were made in all. They were, however, so imperfect that they were destroyed every time when the Kinokawa was flooded. The reparation for flood damages caused a lot of labour and expense to the farmers. Each flume was often extended after the construction, and therefore, the area of irrigated land gradually increased. It was after the middle of the Tokugawa Era, when civil engineering advanced, that the great Kinokawa itself began to be utilized. By dint of civil engineering works there was a rapid cultivation of paddy fields along the Kinokawa, and thus, the Kinokawa Plain came to yield the highest rice-crop in Wakayama Prefecture and attained economical prosperity. 3. Every flume runs long and crooked along the higher part of the irrigated land ; the flume flowing from ‘Oda Dam’ is 32 km long, the longest one from ‘Fujisaki Dam’ 18km, and the shortest one from ‘Anrakugawa Dam’ is 3.5km ; it takes a great deal of labor to keep up these long flumes. ‘Oda Dam’ irrigates the largest area of land i.e. 1, 072 h. a. and ‘Shichigo Dam’ the smallest i.e. 126 h. a. The flumes run on such a sandy and conglomeratic land that they lose 37.5% to 50% of the water on their way ; therefore famers have invented all the possible devices to keep the water of paddy field from being lost. In making the plan for reconstruction of many dams destroyed by the flood in 1953, they decided to give a complete improvement on the old dams. These old dams were integrated into the present four ones of modern concrete type; moreover, the flumes are also being rebuilt into concrete type to prevent water-escaping. 4. The water-supply from the Kinokawa starts on June 15 and lasts to the middle of September. There is a strict provision on sharing of the water-supply. The flumes are equipped with a lot of facilities for distribution of the water. The share of the water-supply is decided by special persons.