In order to clarify the rainfall-runoff processes in a granitic mountain catchment, we conducted hydrological observation in a soil degradation catchment of Setouchi Region. Streamwater, soilwater and rainwater were collected as well as runoff observation. In addition, electrical sounding were carried out at many plots on recharge area by four pole method. The relative resistances at the inside of a mountain changed heterogeneously. Relative resistance variations at the depth of 15m indicated groundwater recharge exists through fissures. NO3-N and SiO2 tracers showed the storm runoff is composed of other component as well as mixing water of soilwater, rainwater and shallow groundwater. These results including the observed recharge process suggest that this component is composed of deep groundwater via fissures. The SiO2 concentration in streamwater decreased with increase of the runoff amount. Counterclockwise hysteresis was found between the SiO2 concentration and the higher concentration appeared in the later events. It suggests the contribution ratio of deep groundwater increases at the latter half of each event and in the later events.
