Abstract
1. The groundwater of the -Zidare River alluvial fan is supplied mainly by the No River, not only in that part of the area where the stream exists, but also where there. are no. streams. In the lower half of this alluvial fan, the water of the Midare River and the Oshikiri River are added to the water of the No River. The groundwater by the Shiromizu River is very scanty.
2. In the upper continously flowing part of each river influent seepage is observed. In the lower reaches, where there are no streams, effluent seepage occurs. In the lower reaches of each river there is a mutual relation between groundwater and the influent seepage in the cases where there are streams. In cases there are no streams, there is a mutual relation between effluent seepage and groundwater.
3. The level of the groundwater has been studied in the Osanagi-go, located in the central part of the fan. This level shows a “ridge and valley-like” character.
4. The principal cause of the dearth of wells in the Osanagi-go is that they are situated in the ridge of groundwater, and that the degree of digging is small.
5. The rising of the groundwater table after a heavy rain is remarkable in the areas near the banks of the rivers and near the hillocks on the top of the alluvial fan.
