1990 年 32 巻 2 号 p. 81-90
The groundwater level in paddy field area fluctuates periodically, high in the irrigation period am low in the non-irrigation period. The magnitude of such water level fluctuation is one of the importan elements related to demands of water for agricultural use. So, it is significant to grasp the distributioi of the fluctuation from the viewpoint of agricultural water use. In this paper, the regional annua groundwater level fluctuation is estimated by the kriging technique, taking up the Echi River Fan as case where the area of paddy field is more than half of the whole area. Anisotropy in the used variogram is also examined, compared with results from simulated data. As a result, the following points be come clear :
(1) When examining variograms of groundwater level fluctuation for the four principal directions_ little anisotropy is found in the direction of Echi River flow. No remarkable differences, however, at-, found in the other three directions.
(2) The groundwater level fluctuation is greater on the left side of the Echi River than on the righ one. Comparing the top part with the end part of the Fan, the fluctuation in the latter is greater that one in the former.
(3) The average groundwater level fluctuation all over the Echi River Fan is range from 1.7m ti 2.0m during 1985-1987.