Study on Effect of Characteristics of River Boundaries on Sediment Transport Process

研究冲积过程的关键是阐明水流特性、泥沙运动和河床或河道形态之间的相互作用。因此，任何泥沙运动的物理模型都必须合理地描述冲积过程的非平衡状态。从这一观点出发，近年来，人们根据对泥沙运动机理的认识，对泥沙模型进行了重新研究。在本研究中，首先探讨边界特性对流动结构的影响。特别地，对粗糙透水床面上的流速分布和湍流结构进行了研究。砾石河床具有相对淹没度小、坡度大的特点，其水流阻力和泥沙输移特性与砂床有所不同，许多冲积河道资料对砾石河床的研究不适用。水流阻力和泥沙输运力学与代表湍流结构的速度剖面密切相关。因此，在本文中，流动结构进行了讨论，特别是大粗糙度和高渗透性的床的影响，使用仔细测量的速度剖面数据。其次，特别是重视统一处理推移质，考虑到推移质运动通过起动和输移过程向悬浮的转变，并应用随机方法提出了描述非平衡状态的物理模型。进而为了预测河岸冲刷过程、护面的形成、泥石流的发生等，讨论了河道边界如边坡、泥沙混合物、透水河床等对泥沙输移过程的影响。

The key to the study of an alluvial process is to elucidate interactions between flow properties, sediment movements and bed or channel configurations. For this reason, any physical model of sediment transport is required to describe reasonably the non-equilibrium state of an alluvial process. From this point of view, the sediment model has been recently reinvestigated on the basis of knowledge accumulated on the mechanism of sediment motion. In this research, firstly, effect of the characteristics of the boundaries on the flow structure is investigated. Particularly, the special attention is paid to the velocity profile and turbulent structure over a rough permeable bed. A gravel bed is characterized by small relative submergence and steep slope, the flow resistance and the sediment transport behaviours on which are somehow different from those on a sand bed.Many informations collected for alluvial channels are on longer valid for gravel-bed rivers. The flow resistance and the sediment-transport mechanics are closely related to the velocity profile which represents the turbulent structure. Thus in this paper, the flow structure is discussed with particular reference to the effects of large roughness and high permeability of a bed, using carefully measured velocity-profile date. Secondary, Particularly, importance is attached to unified treatment of bed material load, taking into account the transition from bed load motion to suspension both through incipient motion and transport process, and a physical model for description of non-equilibrium situation is proposed by applying a stochastic approach. Further in order to predict the scouring process of river banks, formation of armor coat, incipience of debris flow, etc., the effects of channel boundaries such as side slope, sand mixtures and permeable bed on sediment transport process are discussed.