Comparative study on discontinuous nature of sediment transfers and changes of watershed management in river systems

对日本流域进行了流域网分析，考察了霍顿定律。结果表明，基于流序的河道分类可以反映河道形态的规律性和区域输沙特征，可以有效地比较流域水平上河流间输沙特征。利用Kuroki的稳定通道理论，分析了客观流域的沿河道泥沙分布。结果表明，稳定河道形态的变化可以代表河流输沙的特征。研究了九州一忠河上游山区基岩河道不稳定泥沙淤积的调整、北海道Sorachi河河道形态动力学估算的河床物质输运、日本中部天龙河上游地区*的地貌特征和产沙量的时间序列运动，以及日本中部大义河上游浅层滑坡的产沙平衡和产沙量。因此，河道泥沙淤积对于理解泥沙运移的不连续特性至关重要，而流域系统中泥沙淤积的分布及其随洪水事件的变化对于理解流域水平泥沙运移动力学至关重要。此外，确定河道是否处于供应限制条件或运输限制条件也很重要，因为水流功率和泥沙可利用性之间的不平衡导致泥沙淤积。

We conducted the drainage net analysis to examine the Horton's laws in Japanese basins. As a result, it is suggested that channel classification based on the stream order is effective to compare the characteristics of sediment transport between rivers in a basin level because the classification could represent regularities of channel form and the regional characteristics regarding sediment transport. We also analyzed sediment distributions along the river course in objective basins using the theory of stable channel by Kuroki. As a result, it is suggested that the variation from stable channel forms could represent the characteristics of sediment transport in rivers. Furthermore We examined the adjustment of unstable sediment stored in a mountainous bedrock channel of the upper Hitotsuse River, Kyushu, the bed-material transport estimated from channel morphodynamics of the Sorachi River, Hokkaido, the geomorphological properties and the time series movement of sediment yield in*the upper area of the Tenryu River, central Japan, and the sediment budget and sediment yield due to shallow landslides in the upper River Oi, central Japan. As a result, it is suggested that sediment storage in channels is most important to understand discontinuous nature of sediment transfers, and also the distribution of stored sediment in a drainage system and its changes by flood events are important to understand the dynamics of sediment transport in a basin level. Furthermore it is important to identify whether a channel is in supply limited condition or in transport limited condition because the imbalance between the stream power and sediment availability causes sediment storage.