| Research Abstract |
The field evidence collected in the 1970's showed that in forested hillslopes, infiltration capacities almost always exceeds the rainfall intensities. In Japan, Hinoki (Chamecyparis Obtusa) plantation distributes widely because of the expensive log price. In unmanaged Hinoki plantations, understory vegetation decreases and the litter of Hinoki is known to be likely to move downward. Therefore, from the field observation, Hortonean overlandflow may occur. In addition, the soil erosion in Hinoki plantation has been the serious problems in Japan. In this study, we monitored the runoff in small catchments in unmanaged Hinoki plantations to understand the importance of Hortonean overland flow for understanding the human impact on hillslope stormflow path in Japan.
The study catchments locate in Ohmiya village, Mie Prefecture, central Japan. We installed two Parshall flumes in unmanaged Hinoki plantations, and one in broad leave tree area. Electrical conductivity of runoff water is monitored continuously and in selected storm events, in situ water sampling was conducted 1 or 2 hour interval and dissolved ions were analyzed. When the rainfall intensities were high, runoff peaks coincide with rainfall peak in unmanaged Hinoki plantations, but runoff peaks were low and sometimes delayed to the rainfall peak in the broad-leaf forest. The storm hydrograph in Hinoki plantations were separated into two or three components, using electrical conductivity and Cl ions. When rainfall intensity was high, rainfall components occupied 49-67% of the storm hydrograph. This shows that the importance of the rainfall components in overland flow during rainstorm in unmanaged Hinoki plantations
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