急勾配大規模扇状地にみられる流路形態に流域地質が及ぼす影響

抄録

According to the past experiment by Kodama et al. (1987), it was revealed that the grain size distribution could influence the feature of channel morphology. This study aims to verify this result from the fields’ condition. In this study, five alluvial fans include three basin geology, were selected. The channel morphology was analyzed by organizing past studies, materials, and topographical maps, and the bed materials were measured from fan’s apex to toe. The result shows that in the granite rock basin, all channels diverge from the joint fan-head trench due to the repetition of erosion and sedimentation in fan-head trench. Conversely, in the volcanic rock basin, because of lack of fine material, sheet flood domains on alluvial fan leads all channels to diverge from the fan-head. Finally, in the accretionary complex basin, the bed material is finer than other basins so that shallow channels diverge from the fan-head. It makes overflow occurs along the channels, and the main channel swings laterally to spread small channels all over the alluvial fan.