Spatial Variation in Specific Discharge of Base Flow in a Small Catchments, Oe-Yama Region, Western Japan.

Abstract

Base flow from 66 tributaries in watersheds underlain by serpentinite, granite, and Paleozoic shale were measured in Oe-yama region, Kyoto Prefecture, Western Japan. The base flow measurements sufficiently after rainfall were conducted during the snowmelt season (April) and summer dry season (August). Spatial variation of specific discharge was greater in the serpentinite basins than those in the granite and the Paleozoic shale basins. In addition, there are many tributaries without discharge in serpentinite basins, even though they have large drainage areas and well-defined valleys. On the contrary, the specific discharges in the granite and the Paleozoic shale basins are relatively constant among tributaries. The average specific discharges in the serpentinite basin are smaller in August than that in April, whereas little difference between base flow discharges of April and August were observed in both the granite and the Paleozoic shale basins. These findings suggest that the seasonal variation of groundwater table level in bedrock is larger in serpentinite mountainous region than that of the granite and Paleozoic shale areas. Hence, we expect that lithology has a crucial effect on spatial variation, quantity and seasonal change of base flow.