Effects of weathered granitic bedrock on runoff processes in a small headwater catchment

Recent studies have suggested large influences of bedrock groundwater on runoff generation, water chemistry, and landslides occurrences in headwater catchments. In order to clarify physical water flow process between soil and shallow bedrock, and its effect on storm and base-flow discharge processes in a small headwater catchment underlain by weathered granite, this study conducted hydrometric observations using soil and bedrock tensiometers combined with numerical simulation analyses. Results showed that, in an unchanneled 0.024- ha headwater catchment, saturated and unsaturated infiltration from soil to bedrock is a main hydrological process at the soil-bedrock interface. Annual bedrock infiltration ranged 35 to 55％ of annual precipitation and increased as precipitation increased, suggesting a large potential of bedrock infiltration, which was partly explained by a large buffer capacity of soil layer overlying the bedrock. Physical property of soil layer was an important factor to control generations of bedrock infiltration and saturated lateral flow over the bedrock