摘要
山区河流受暴雨洪水、滑坡和泥石流等灾害的影响,漂石颗粒在河床不断集聚,从而改变局部区域的河床形态及其水流结构。作者基于对野外典型漂石河段的调查和室内概化水槽试验,指出了河床变形及水流运动对漂石的突变响应特征。试验床面分别预铺粒径为2.5和7.0 mm的均匀沙,并在其上放置粒径为15.7 cm的天然漂石,利用声学多普勒测速仪和全站仪测量漂石局部区域的水流结构及河床冲淤地形。试验分析表明:漂石河床局部调整受相对淹没度和床沙粒径的影响,随着相对淹没度的变化,冲坑深度及范围也随之调整,但淤积的最大高度值则趋于稳定;床沙粒径与冲坑深度、范围呈现出较好的线性正相关关系,但其对后者的影响要远大于前者。漂石河床的局部响应主要是因为漂石的存在促使其局部区域的水动力条件变化。在无床沙工况下,漂石局部近底流速分布随着相对淹没度的变化而变化,而在有床沙工况下,其对相对淹没度的变化却并不敏感,但它们都较为符合对数分布。漂石局部的紊动强度及紊动耗散均在漂石下游的Δx≤1.5D范围内出现陡增现象,且随着床沙粒径的增加,紊动强度陡增的幅度变小,其影响范围也随床沙粒径及相对淹没度的变化而变化。因此,山区河流河床漂石对水流运动及河床变形的作用主要表现在局部近底水流结构及紊动统计特征出现陡变特征,从而引起局部冲淤程度加剧,对河床的水沙运动及其稳定形态产生较大影响。
There is a higher frequency of rainstorm flood,landslide and debris flow occurring in mountainous area,causing the accumulation of boulders on river beds,changing locally the bed form and flow structure.The experiments were conducted in a moveable channel bed made of sorted sediments with D1=0.025 m and D2=0.07 m,respectively.A down-looking Son Tek acoustic Doppler velocimeter(ADV) was equipped to record the rapidly responding flow movement so as to analyze the field turbulence and sediment transport.The bed topography was measured by total station.From the experimental results,it can be concluded that the relative submergence and sediment size exerts a strong control on channel morphology in the vicinity of the boulder,such as the depth,range of scour hole and the deposition height downstream,and there are good linear correlations among the sediment size,the depth,and range of scour hole.The analysis of the experimental data reveals that the velocity in the bottom portion of the flume(down to 0.2 of the relative flow depth(y/h)) preserves logarithmic law:in clear water,and the increase of the relative submergence leads to the reduction of the related parameters of velocity distribution;while the velocity in the bottom portion of the flume is insensitive to the relative submergence with grain underlying.Besides,the mixing process downstream of the boulder causes a considerable variation in the wall-wake zone,which exhibits a steep rise in turbulence intensity and turbulence dissipation at the range of the 1.5 times of the boulder distance downstream,and a gradual recovery with distance downstream of the boulder.The amplitude and region of influence of boulder on turbulence changes with the bed material grain size and the relative submergence.As a summary,the boulders result in dramatic increase of statistical characteristics of near-bottom flow structure and turbulence,which enhance the scouring and siltation,and have an important influence on the water-sediment movement and its stable form.
出处
《四川大学学报（工程科学版）》
CSCD
北大核心
2017年第3期22-28,共7页
Journal of Sichuan University (Engineering Science Edition)
基金
国家重点研发计划重点项目(2016YFC0402304-1)
国家自然科学基金资助项目(51579163
51639007)
关键词
山区河流
漂石
河床突变响应
水流结构
紊动强度
mountain river
boulder
channel mutation response
flow structure
turbulent intensity
