山地河川における小規模ダムの上下流区間の特性による礫移動の違い

抄録

We investigated bedload transport of marked particles (10cm, 20cm, 30cm) after an annual flood at 5 different reaches in the upper and lower sections of Kurobe dam, in a mountain river, using a radio tracer tracking technique. Marked particles moved more frequently in the lower reaches of the dam, while none was moved at the immediately upper of the dam, where channel was very gentle and wide. The size of transported particles in each reach coincided with the maximum movable size predicted by tractive force from channel gradient, width, and discharge except in cases where huge boulders affected local flow velocity. These results support our previous prediction that transport of particles with >20cm was prevented at immediately upper reach of the dam even during larger floods. Our results also suggest that a large increase in discharge by tributaries at the dam site promote particle transport and expansion of bedrock exposure in the lower reaches of the dam.