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

我们进行了水系分析，以检验日本盆地的霍顿定律。结果表明，基于水系顺序的河道分类能较好地反映河道形态的规律性和输沙的区域性特征，是比较流域层面河流输沙特征的有效方法。并利用黑木的稳定航道理论分析了目标流域的泥沙分布。结果表明，稳定河段形态的变化能较好地反映河流输沙特征。此外，我们还研究了九州日津河上游山区基岩河道中不稳定泥沙的调节，从北海道索拉奇河河道地貌动力学估计的底质输运，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，以及日本中部大江河上游浅层滑坡的泥沙收支和产沙量。结果表明，河道泥沙蓄积对了解泥沙输移的不连续性质是最重要的，而泥沙在流域系统中的分布及其随洪水事件的变化对于了解流域层面的泥沙运动也是非常重要的。此外，重要的是要确定河道是处于供应受限的状态还是处于运输受限的状态，因为水流功率和泥沙可获得性之间的不平衡会导致泥沙储存。

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.