Abstract
To investigate the formation process of Horton overland flow in unmanaged Hinoki plantation, hydrometric observation and tracer approach were applied in an unchanneled catchment, Mie prefecture, central Japan. An overland flow with a total runoff rate of 15.7 mm was observed during a rainstorm with a total rainfall of 120.4 mm. The peak discharge of overland flow coincided with the peak rainfall, and major solute ion concentrations decreased obviously with runoff peak. End member mixing analysis was applied to evaluate the overland flow components using electrical conductivity and Cl- concentration as tracers. The ratio of rainfall component to the overland flow was estimated to be ranging from 24 to 84 %. Especially, the rainfall component was predominant in heavy rainfall intensity more than 2 mm/5min. The overland flow occurring in a rainstorm more than 2 mm/5min should be Horton overland flow considering the end member mixing analysis results and runoff characteristics. This shows an importance of the Horton overland flow in rainfall-runoff processes in the catchments covered by unmanaged Hinoki plantations.
