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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Flow in a tightly curving meander bend: Effects of seasonal changes in aquatic macrophyte cover
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Flow in a tightly curving meander bend: Effects of seasonal changes in aquatic macrophyte cover

机译：弯曲弯曲的弯道中的水流：水生植物盖层季节性变化的影响

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摘要

The effects of aquatic macrophytes on flow and turbulence were studied in a tightly curving meander bend. Three field measurement campaigns were carried out within a one year period to capture effects of seasonal changes in macrophyte cover. They comprised three-dimensional velocity measurements and mappings of vegetation cover and bathymetry. Flow accelerates and converges over the run into an axial pool in a jet-like flow pattern bordered by outer and inner bank flow separation zones. The jet and widening of the cross-section anticipate helical flow until the second half of the bend, where an asymmetric pool developed. Submerged vegetation at the riffles preserves the jet at much lower discharges during the summer period by concentrating high momentum fluid near the surface. Plants locally modify the velocity and stress patterns, reduce bed shear stresses, create zones of fine sediment accumulation and reinforce the bed and banks with roots and rhizomes. Plant patches colonising the banks and the point bar confine secondary flow cells laterally and affect shape and magnitude of the transverse flow profiles near their edges. The morphology of the bend was very stable over the observation period and neither bank erosion nor pool scouring occurred. However, fine sediments accumulate within vegetation patches and in the recirculation zones while the remaining open areas tend to erode slightly. With the decay of macrophytes in winter, sediment accumulations are mobilised again and the bathymetry levels, supporting cyclic models of morphologic change in vegetated bends. In the second part of the paper, semi-empirical models for the three predominant flow types were tested and discussed; velocity and stress models of vegetated mixing layers and plane turbulent jets, and Rozovskii's model for the transverse flow in bends.
机译：在紧密弯曲的弯道中研究了水生植物对水流和湍流的影响。一年内开展了三个野外测量活动，以捕捉大型植物覆盖率的季节性变化影响。它们包括三维速度测量以及植被覆盖和测深图。流量在整个运行过程中加速并收敛到轴向池中，呈轴向流动状，并以外部和内部堤流分离区为边界。射流和横截面的扩大将预料到螺旋流，直到弯曲的下半部分，在那里形成不对称的池。在夏季，浅滩上的淹没植被通过将高动量流体集中在地表附近，使喷流保持在较低的排放量。植物会局部改变速度和应力模式，减少床剪应力，形成精细的沉积物堆积区，并用根和根茎加强床和河床。在堤岸和点杆上定植的植物斑块横向限制次生流动池，并影响其边缘附近的横向流动剖面的形状和大小。在观察期间，弯曲的形态非常稳定，既没有堤岸侵蚀也没有池冲刷。但是，细小的沉积物会堆积在植被斑块内和再循环区域内，而其余的开放区域往往会受到轻微侵蚀。随着冬季大型植物的腐烂，再次动员了沉积物积聚和测深，这支持了植被弯道形态变化的循环模型。在本文的第二部分中，测试和讨论了三种主要流动类型的半经验模型。植被混合层和平面湍流射流的速度和应力模型，以及弯道中横向流动的Rozovskii模型。

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