The constitution of the gravels consisting of the Nasuno alluvial fan, Tochigi Prefecture, is very heterogenous. Namely the river channel deposits have a large porosity and movement of ground water is rapid, but the fluviated gravels Covering the higher parts of the basements, contain generally clayey materials and they are impervious to movement of ground water. The maximum velocity of ground water which was observed in the well is about 100 meters. an hour. In not a few cases, the velocity of ground water through the gravels of the valley fill is more than 10 meters an hour. As for making use of ground water in this area, it must be important.