摘要
天然河道中坝田滞水区的低速环流特点能够促进泥沙淤积,延长营养盐滞留时间,为水生植物提供良好的生长环境。关于滞水区水动力学的研究已有诸多成果,然而植被影响下的滞水区流场分析却鲜有报道。本文采用模型试验研究了挺水植被作用下滞水区水流结构与泥沙落淤问题,其中,在清水条件下采用粒子图像测速法(PIV)测量了流场结构,在浑水条件下采用拍照、称重以及粒度分析等手段调查了淤沙现象。试验结果表明:植被群落可以削弱滞水区环流速度,并造成环流模式发生变化,即从无植被条件下的双环流结构调整为有植被条件下的单环流结构;另外,植被会抑制混合层拟序涡的发展,导致涡体尺寸明显减小。由于丁坝群的连续挑流作用,主渠泥沙主要以细颗粒悬移质形式进入滞水区,包括两种途径,一种是跟随环流结构进入空腔,另一种是跟随交界面紊动涡体扩散到空腔。由于泥沙运动受制于水动力特性,无植被与有植被两类工况下,水流结构的不同会导致滞水区淤沙结果存在一定区别,即同等历时内,无植被滞水区的淤沙颗粒粗,落淤质量大,淤积物主要集中在主环流区域;在植被化工况中,植被群落的约束作用会降低Kelvin-Helmholtz剪切层摆动强度以及抑制空腔-主渠之间的水体交换过程,导致滞水区泥沙颗粒细,淤沙少,淤积物几乎均匀地分布在整个滞水区。这些差异在上游滞水区(即水力特性沿程发展的过渡阶段)体现尤为明显。
The low-velocity circulation pattern in groyne fields could promote the sediment deposition and lengthen the mean residence time of nutrients, thus creating a favorable growth environment for aquatic plants. Although flow hydrodynamics in cavity zones had been well studied,vegetation effects on the recirculating flow were rarely considered. Laboratory experiments were adopted to investigate the flow structure and sediment deposition in groyne fields with emerging vegetation, where the PIV(particle image velocimetry) was employed to measure the velocity vector in clean water and the combined method of photo, weighing and particle size analysis was used to investigate the sediment phenomenon in muddy water. The results revealed that the presence of vegetation reduced the circulation velocity and rearranged the circulation systems inside the cavity, i.e. from the double gyres to a sing one. In addition, the plants suppressed the evolution of coherent eddies in the mixing layer, with a distinct decrease in the eddy scale. Due to the deflecting effect of consecutive groyne on the main-stream, sand in the main channel was transported into the groyne field in a form of fine suspended load through two ways, i.e., by the circulation structure and by the turbulent vortex at the interface. As the sediment transport was subject to hydraulic characteristics, different flow structures between the non-vegetated and the vegetated cases could lead to the difference of sediment deposition. Under the same diachronic condition, the deposition with the coarse particle size and the relative large weight was mostly concentrated in the primary circulation area in the non-vegetated case;but for the vegetated condition, as the restriction effect of vegetation community could reduce the oscillation intensity of Kelvin-Helmholtz shear layer and the water exchange coefficient between the cavity and the main channel, the deposition with the fine size and the small weight was almost evenly distributed in the whole groyne filed. Such differences were particularly evident in the upstream groyne fields(i.e., the transitional stage of of hydraulic characteristics).
作者
向珂
杨中华
XIANG Ke;YANG Zhonghua(State Key Lab.of Water Resources and Hydropower Eng.Sci.,Wuhan Univ.,Wuhan 430072,China)
出处
《工程科学与技术》
EI
CAS
CSCD
北大核心
2021年第1期85-93,共9页
Advanced Engineering Sciences
基金
国家自然科学基金面上项目(51879199
51679170)。
关键词
滞水区
植被
模型试验
水流结构
泥沙落淤
groyne fields
vegetation
model experiment
flow structure
sediment deposition
作者简介
向珂(1991-),男,博士生.研究方向:环境及生态水力学.E-mail:kxiang@whu.edu.cn;通信作者:杨中华,E-mail:yzh@whu.edu.cn。
