Mechanics of Stable Straight Channel or Braided Channel Formation

研究了直流道达到稳定平衡状态的过程。这一过程可分为两类：(1)当初始河道宽度大于稳定河道宽度时，由于岸坡冲刷引起的河道加宽过程；(2)由于水流不稳定而引起的水边泥沙淤积而引起的河道变窄过程。日本建设省公共工程研究所的研究人员通过实地调查报告了这两个过程。在这项研究中，模拟的过程是在一个实验水槽。建立了数值模拟模型来了解这一过程，并研究了辫状河网的形成过程。对裸露坡面上的河网形成和水槽中的辫状河形成进行了试验研究，重点考察了这两个过程之间的相似性。其机制已被理解。例如，地下水流在这种形成中起着重要的作用。还获得了一些其他有趣的信息。在实验研究的基础上，建立了有限条件下的数值模型。这将在未来扩展到更复杂的版本。正如作者在最初方案中所预期的那样，上述两个过程的机制都得到了明确的阐述。

The process in which a straight channel reaches a stable equilibrium state was investigated. The process is classified into a following two categories ; (1) channel widening process due to a bank erosion in case that the initial channel width is larger than the stable one, (2) channel narrowing process due to a sediment deposition around a water margin which is caused by the unsteadiness of water discharge. Such two processes were reported through the field investigations by the researchers in Public Works Research Institute, Ministry of Construction, Japan. In this study, the processes were simulated in an experimental flume. Numerical simulation model was also constructed to understand the process itself.The process in which a braided channel network forms was also investigated. Channel network formation on a bare slope as well as a braided river formation in a flume was studied experimentally with a focus attention on the similarity between these two processes. The mechanism was understood. For example, subsurface flow plays an important role in such formation. Some other interesting information was also obtained. Besides the experimental investigation, numerical model was developed in some limited conditions. This will be extended in more sophisticated version in future.The mechanisms of the above two processes were made clear as the author expected in the initial plan.