Origin of Bedforms in a Scale of Valley Width and Their Effect on the Sediment Transport in Mountain Rivers

河谷宽度尺度的河床成因及其对山区河流输沙的影响

• 批准号: 13650558
• 负责人: HASEGAWA Kazuyoshi
• 金额: $ 2.11万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650558/
• 关键词: mountain river; bedform; bifurcated channel; concentrated channel; alternation bars; sediment transport; channel blocking; alternating channel change; 河床形態; 分岐流路; 不安定堆積土砂; 交互分級波

In a mountain river, large scale bedforms to be in a scale of several times of the valley width can be seen, which closely correlate with the channel branching and gathering. Movable bed experiments were conducted by using sediment materials with mixed grain size to find the origin of the bedforms and their effects on the sediment transport in the downstream channels. The results showed :(1) Double row bars generated in the initial channel under a fully spreading flow in the whole channel width (valley width) closely resembles a natural large scale bedform, then it can be concluded that the large scale bedforms are very double row bars generated by a large flood.(2) Bifurcated and concentrated channels with large scale bedforms are deeply eroded in the portion of bends by a medium or small flow discharge. This means that large scale bedforms can be sediment resources for medium or small floods.(3) Node points were ovserved where upstream channels concentrate and bifurcate just downstre … More am. At the points, alternating change of main flow occur from one bifurcated channel to the other one to play an important role for chenge of sediment transport rate in the downstrem channels.Extracted experimental tests for bifurcated channel flows were carried out by using a Y-shape channel, in order to elucidate the mechanisms of alternating change of main flow. As the result, the followings ware found :(1) The phenomenon is caused by the effect of an alternating bar in the upstream channel. It does not occur in any case with no bars.(2) The alternating change of main flow does not arise from the migration of upstream bar, but from the storong deviation of flow toward one side bank in the upstream channel due to bar. While much sediment discharge toward one side channel drives to block the entrance, that induces change of flow course to another channel.(3) These mechanisms could be formulated by simultaneous 1-D differential equations for bed evolution, which summarized to a dumping oscillation equation. From the equation, oscillation condition was found. Less

在山区河流中，可见数倍于河谷宽度的大型河床形态，这与河道的分岔和聚集密切相关。利用混合粒度的沉积物进行移动床实验，探讨床形的成因及其对下游河道泥沙输运的影响。研究结果表明：（1）在全河道宽度（谷宽）内水流充分铺展的情况下，初始河道生成的双排坝与天然大型河床形态极为相似，由此可以判断，该大型河床是大洪水形成的双排坝。（2）大型河道的分叉集中河道，在中小流量的流量作用下，在弯道部分被深度侵蚀。这意味着大型床型可以成为中小型洪水的沉积物资源。(3)观察到上游河道集中并在下游分叉的节点。在这些点上，主流从一个分叉河道到另一分叉河道发生交替变化，对下游河道输沙速率的变化起着重要作用。利用Y型河道进行了分叉河道流量的抽提实验试验，以阐明主流交替变化的机制。结果发现：(1)该现象是由上行通道中交替条的影响引起的。在没有坝的情况下都不会发生这种情况。(2)主流的交替变化不是由上游坝的迁移引起的，而是由于坝的作用而使水流向上游河道的一侧岸发生了严重的偏离。当大量沉积物向一侧河道排放时，会堵塞入口，从而导致流向另一河道的流道发生变化。(3)这些机制可以通过床演化的联立一维微分方程来表达，该方程可概括为倾倒振荡方程。从方程中，找到了振荡条件。较少的

项目成果

目黒嗣樹, 長谷川和義, 中村健作: "山地河川における分岐流路変動と土砂移動に関する実験的研究"水工学論文集. 46巻. 755-760 (2002)

Tsugumi Meguro、Kazuyoshi Hasekawa、Kensaku Nakamura：“山区河流分支河道波动和泥沙运动的实验研究”水利工程学报第 46 卷，755-760 (2002)。

目黒 嗣樹: "山地河川における分岐流路変動と土砂移動に関する実験的研究"水工学論文集. 46. 755-760 (2002)

目黑黍：《山区河流支流河道波动与泥沙运动的实验研究》水利工程学报46. 755-760（2002）。

Meguro, H.: "Experimental Reproduction of Braided Channels and Bedforms with Three Different Scale Obserred in Mountain Rivers"Jour. of Hydroscience and Hydraulic Engineering. Vol.20 No.2. 141-153 (2002)

Meguro, H.：“在山区河流中观察到的三种不同规模的辫状河道和河床形态的实验再现”杂志。

Meguro, H.: "Experimental Reproduction of the Braided Channels and Bedforms in a Mountain River"2nd IAHR Symposium on River, Coastal and Estuarine Morphodynamics. 733-742 (2001)

Meguro, H.：“山区河流辫状河道和河床形态的实验再现”第二届 IAHR 河流、沿海和河口形态动力学研讨会。

Hasegawa, K., Hirose, K., Meguro, H.: "Experiments and Analysis on Alternating Mainstream Change in the Bifurcated Channel in Mountain Rivers (in Japanese)"Annual Journal of Hydraulic Engineering, JSCE. Vol.47. 679-684 (2003)

长谷川，K.，广濑，K.，目黑，H.：“山区河流分叉河道主流交替变化的实验与分析（日文）”水利工程学报，JSCE。