1985 年 27 巻 4 号 p. 157-170
We discussed basic characteristics on the groundwater bearing conditions of the Dejima area in our first report. The present report is concerned with the result of subsequent detailed research on groundwater flow systems in the experimental basin.
Table 1 summarizes the major arguments of our study. At first, we divided the groundwater flow systems of this area into three category from their spacial scale. That is to say, the partial scale, the local scale and the regional scale.
The dominating factors on the groundwater flow systems are different according to the above mentioned scale. In the case of the small scale, the groundwater phenomena, for instance“ concentrated flow of groundwater”, are more intensively affected by the geological factors rather than topographic conditions.
On the other hand in the case of the regional flow system of which scale covers one drainage basin, the topographic conditions come up as the dominating factor for groundwater flow systems.
Next, in this paper, we emphasized the human activities on groundwater. Especially, irrigation to paddy fields becomes so large that it can no more be disregarded as compared to natural factors.
The examples of such case are given below.
1) In the paddy fields which are irrigated in summer season, the groundwater level rises about 2-4m compare with the other areas.
2) Ephemeral groundwater mounds or artificial groundwater mounds appear in the paddy areas within summer season.
3) The direction and velosity of groundwater flow vary with the above mentioned conditions.