ANALYSIS OF STREAMFLOW-GENERATING MECHANISMS BASED ON RAINFALL-RUNOFF RESPONSES AT A HILLSLOPE

The effects of water discharging from landscape units, such as hillslope and riparian, on runoff generation at catchment-scale are poorly understood. We analyzed the streamflow-generating mechanisms at a catchment outlet (103ha) based on rainfall-runoff responses at a hillslope (0.65ha) in a headwater catchment. On rising limb of streamflow hydrograph, the streamflow was closely related to saturation excess overland flow from spring area at the hillslope bottom, and peak discharge of streamflow depended on 30-min rainfall amount just before the time of peak discharge. These indicated that the dominant component of the peak discharge of streamflow is saturation excess overland flow from the near stream channel. On recession limb of streamflow hydrograph, baseflow discharge and recession coefficient depended on saturated subsurface flow above soil-bedrock interface at the hillslope and its decreasing rate, respectively. We conclude that hillslopes and riparian play discrete roles in runoff generation at the catchment outlet, and well-observed hillslopes can be useful for understanding the runoff generation.