Spatial variation in streamflow generation in a small forested catchment in Japan

Abstract:

Spatial variation in streamflow generation was studied in a small and steep headwater catchment to clarify the spatio-temporal water yield pattern. Streamflow were gauged at three locations in 170 m long stream, and groundwater elevations and soil moisture were also monitored in the catchment. Results showed that, for base flow, the upstream water yield surpassed the mid- and downstream water yield during the rainy season and kept higher yield during the large recession periods. The timing when the upstream water yield became larger than downstream water yield overlapped with the timing when groundwater upwelling was observed in the area where the stream starts, indicating the groundwater upwelling at the base of zero-order basin increased the relative size of upstream water yield. For the event flow, the relationship between soil moisture and streamflow was used to determine the potential connectivity between hillslope and stream. Among a total of 57 events identified in 2013, hillslope subsurface flow was generated in 13, 19 and 28 events in up-, mid- and downstream hillslope, respectively. The steeper valley structure and weathered bedrock in the downstream portion may be a factor for the more frequent establishment of connectivity. The results of this study demonstrated that the contribution of groundwater at the base of zero-order basin, longitudinal channel gradient and hillslope arrangement produced the spatial variability in streamflow generation in the headwater catchment.