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Study on Critical Conditions of Generation and The Functions of Medium-Scale Bedforms in Mountain Rivers

山区河流中型地貌生成临界条件及作用研究

基本信息

批准号：
11650519
负责人：
HASEGAWA Kazuyoshi
金额：
$ 1.6万
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：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11650519/
关键词：
mountain river bedform alternating bars linear instability analysis sand waves alternating sorting waves Talbot sediment size distribution steep channel experiment with heterogeneous bed materials 砂礫堆分級波急勾配水路実験

项目摘要

The aim of the research is to elucidate the properities of medium-scale bedforms evolving on mountain rivers from view points of the critical condition for generation and the functions to other bedforms and flows. Following results were obtained from steep channel experiments with heterogeneous materials and analyses within the research term :1. It was found from the linear instability analysis for the system of sediment and flow, that there are two significant solutions for maximum growth rate of the perturbations of bed displacement, velocity etc. One corresponds to the growth of alternating bars and the other corresponds to sorting waves of bed gravel and sand.2. A wavelength of an alternating bar growing on a steep channel bed with heterogeneous materials has a tendency to become 3 times longer than a wavelength of bar on an alluvial bed. The alternating bars concentrate the flow with sorting the gravel and sand on the bed to form step-pools.3. Under the hydraulic condition of high shearing stress such the sorting instability dominates the bed elevation instability, a flat bed grows on the bed to form alternating fractions of large size pebbles with spacing in 1.5 times of a bar wavelength.4. Sediment discharge to the two kind of bed form is not clearly different each other.5. Very similar bedform to steps and pools in a natural stream evolved in the experimental channel when ribs superposed alternating bars. The bedform was seen applicable to a fish way as a new type.6. In the experiment of high discharge, multiple rows bars rose on the bed. When a small discharge flow was run on this bed, braided channels occurred with medium-scale bars and ribs ; the morphological feature was very close to that of a natural mountain river.7. Large-scale bed undulation caused by the multiple rows bars and change of the braided channels give a great influence to the discharge of sediment at the end of the experimental channel.

研究目的是从形成的临界条件和对其它床型及水流的作用等方面阐明山区河流中尺度床型的演变特征。通过对陡槽非均质材料试验和分析，取得了以下成果：1。通过对水流-泥沙系统的线性不稳定性分析发现，河床位移、流速等扰动的最大增长率存在两个显著解，一个对应于交错沙坝的增长，另一个对应于河床砾石和沙粒的分选波.在具有非均质物质的陡河床上生长的交替沙坝的波长有变成冲积河床上沙坝波长的3倍长的趋势。交错的沙坝使水流集中，分选河床上的砾石和砂，形成阶梯状的滩槽。在高剪应力条件下，分选失稳主导床面高程失稳，在床面上形成一个平床，形成间距为1.5倍沙条波长的大粒径卵石交替级配.两种床型的输沙量差异不明显.在实验水道中，当棱纹叠置在交替的沙洲上时，形成了与天然河流中的台阶和水池非常相似的底形。该底模作为一种新型底模，可应用于鱼道.在大流量试验中，床面上设置了多排竖栅。当小流量流经该河床时，形成中等规模的沙坝和肋状辫状河道，其形态特征与天然山区河流非常接近.多排拦门沙和分汊河道的变化引起的大尺度河床起伏对试验河道末端的输沙量有很大的影响。