A stud on the mechanism of the formation of multiple and braded bar channels

通过实验、数值和理论研究了多沙洲和辫状流的产生和形成机理。清水利用可动床水槽进行了一系列的物理实验。首先提供排水，形成天然条形池床地形。然后把草籽撒在棒子上，几个星期后就形成了。继续供水，考察植被对河床和堤岸侵蚀的影响。成功地建立了一个数值模型来重现实验中观察到的沙洲形成和河岸侵蚀。应用该数值模型对2003年8月阿佩津河洪水的流量和河床变形进行了研究。长谷川进行了模拟辫状河中水流和泥沙转移和转换的实验。通过实验发现了交变棒特性的重要性，并提出了解释这一效应的理论。将这一结果应用于石别苏河河道改道，对泥沙输运和沙坝的形成进行了解释。Watanabe进行了一个实验，重点研究了非定常流动对棒材产生的影响。确定了水流流量曲线，以产生从交替沙洲到多沙洲的沙洲转变。研究发现，历史效应对动床河道中沙洲的变形有重要影响。在此基础上，系统地研究了多沙洲和辫状沙洲的形成框架，并提出了一种模拟冲积河流河道形成过程的理论和数值模型。

Mechanism of the generation and formation of multiple bars and braided stream were studied by experimentally, numerically and theoretically.Shimizu performed a series of physical experiment using a flume with moveable bed. At first, water discharge is supplied and natural bar pool bed topography is generated. Then grass seeds were strewed on the bar formed and grown up for a few weeks. The water supply was continued and the effect of vegetation to bed and bank erosion was investigated. A numerical model is successfully developed to reproduce the bar formation and bank erosion observed in the experiments. The numerical model is applied to study the flow and bed deformation observed during a flood of the Appetsu River of the August in 2003.Hasegawa performed an experiment to simulate the flow and sediment diversion and conversion in braided stream. The importance of the alternating bar characteristics was found by the experiment and a theory to explain this effect is proposed. This results was applied to the channel diversion of the Shibetsu River, and the sediment transport and the bar formation were explained.Watanabe performed an experiment focused on the effect of unsteady flow to the bar generation. The flow discharge hydrograph was determined to produce the transformation of bars from alternate bars to multiple bars. It was found that the historical effect is very important in for the transformation of bars in the moveable bed channels.Consequently, the framework of the generation of multiple bars and braided bars were investigated systematically and a theory and a numerical model were proposed to reproduce the actual channel formation in the alluvial rivers.