Steep mountainous streams are often characterized by bedrock channel, which temporally causes sediment storage and scouring due to channel obstructions, such as bedrock projection and large rocks. In this paper, the influence of bedrock projection and large rocks on long�]term riverbed changes with sediment transport was statistically examined in a mountainous gorge channel, Oyabu Creek, Kyushu, Japan. This study was conducted based on the 12�]years field monitoring during 1995 and 2007 in a steep mountainous stream, and sediment deposit, scouring, and variation depth with mean bedrock projection area, bedrock relief (wetted perimeter/channel width) and the volume and number of large rocks are calculated from these data and field measurement in 2006. As a result, both of sediment deposit, scour and variation depth were increased with increasing in mean bedrock projection area and volume of large rocks rather than bedrock relief and the number of large rocks. Furthermore multiple correlation analysis of mean bedrock projection area and volume of large rocks with sediment variation depth show high correlation coefficient. Comparing changes in sediment storage depth between bedrock projection segment and non�]projection segment implies that bedrock projection segment caused considerable sediment storage with alternatively deposit and scouring dominated periods within 3 years. These results suggest that mean bedrock projection area and the volume of boulders play an important role on sediment transport providing channel bed relief in a steep mountainous stream.


Key words�Fsteep mountainous stream, bedrock channel , bedrock projection, large rocks, sediment transport