Sediment Yield Variation in Small Catchments with Different Bedrock in a Humid Temperate Region

Abstract

Sediment yield in mountainous catchments is closely associated with habitat stability of ecosystems in floodplain or valley bottom. The results of this study provide potential scenarios of future changes in sediment yield as a result of increasing rainfall due to climatic warming. We monitored stream discharge and sediment yield at four small catchments with different bedrock types and stream orders in a subalpine environment in central Japan. The results showed that bedload materials were yielded continuously in the granitic rock area, but only intermittently during the strong storm runoff in the sedimentary rock area. Our results indicate that future increase in the amount of bedload yield in sedimentary rock area will be proportional to rainfall in the granitic catchments, but may be variable in the sedimentary catchment depending on the sediment availability. The amount of bedload had no linear relation with catchment size. In the longterm, however, the impact on habitat stability can be substantial in both types of catchments, because annual amount of bedload will increase from year-to-year. Nevertheless, out results indicate that an improvement of the existing methods for predicting the trends of bedload yield is needed for the appropriate management and conservation of mountainous watersheds.