Time scale changes in elements of water utilization at irrigation districts after notifying habitual water right

The water utilization for irrigation based on the habitual water right was criticized in 1994 when there was a water shortage because it obstructs the effective water use and flexible interchange of water among water users under the condition of water shortage. The background of these criticisms is that the actal condition of water utilization for irrigation based on the habitual water right are unclear. In other words, the water utilization for irrigation based on habitual water right still continues the way to take water by means of old water utilization method, even if the agricultural environment has been changed greatly. Therefore, in this study, the changes of irrigation elements are analyzed for the period from the time when the habitual water right was notified (1965's) by the River Low to now. Investigation areas are 182 districts arbitrarily selected over the country. Results are shown as follows. (1) Irrigation area The present mean irrigation area has decreased to 88 % of the notified value in 1965's. Five elements that influences the change of the irrigation area are listed below in the important order. 1) type of public facility improvement project carried out the past, 2) mean water requirement in winter, 3) scale of notified irrigation area, 4) mean irrigation requirement in irrigation period, 5) regional agricultural type. (2) Irrigation requirement The mean irrigation requirement in irrigation period is 79 % of the value notified, and it has no synchronization with the change of irrigation area directly. Five elements which influences the change of the irrigation requirement are listed below in the important order. 1) mean irrigation requirement in irrigation period, 2) regional agricultural type, 3) use ratio of regional water resources, 4) type of public facility improvement project carried out in the past, 5) scale of notified irrigation area. By comparing the present irrigation requirement with the notified values, it is revealed that in 44.5 % of the investigated areas, the notified irrigation requirement can be regarded as the same as the mean of the present irrigation requirement. And, in 76.5 % districts of the remained 56.4 % areas, the mean values of present irrigation requirement are less than the notified irrigation requirement. However, because the analysis of irrigation requirement in this paper is only based on the data in 1996, it is necessary to use the data in other years to make the results universal. (3) Winter water intake In 77.5 % of the investigated areas, winter water intake is carrying on, 86.5 % of them use the water for regional water utilization in rural area. 78 % of the regional water utilization are for the purpose of fire prevention, other leading purposes are dilution against polluted flow and environmental conservation. Five elements that influences water intake in winter are listed as follows in the important order. 1) intake method from river, 2) type of manager, 3) irrigation area per farmer, 4) mean irrigation requirement in irrigation period, 5) scale of notified irrigation area