Mechanics of Stable Straight Channel or Braided Channel Formation

研究了直线通道达到稳定平衡状态的过程。该过程分为以下两类；(1)初始河道宽度大于稳定河道宽度时，由于河岸侵蚀导致河道加宽；(2)排水不稳定时，由于水缘周围泥沙淤积导致河道变窄。这两个过程是由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的。在本研究中，在实验水槽中模拟了这一过程。并建立了数值模拟模型来了解过程本身。研究了编织通道网络的形成过程。本文对裸坡上河道网的形成和水槽内辫状河的形成进行了实验研究，重点探讨了这两种过程的相似性。机理被理解了。例如，地下流体在这种地层中起着重要作用。还获得了一些其他有趣的信息。在实验研究的基础上，建立了一些有限条件下的数值模型。这将在将来以更复杂的版本进行扩展。上述两个过程的机制如作者在初始计划中所期望的那样明确。

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.