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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Life of a bifurcation in a gravel-bed braided river
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Life of a bifurcation in a gravel-bed braided river

机译：砾石层辫状河中分叉的寿命

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Channel bifurcation is a key element in braided rivers, determining the water and sediment distribution and hence controlling the morphological evolution. Recent theoretical and experimental findings, as well as field observations, showed that bifurcations in gravel-bed braided rivers are often asymmetrical and highly unstable. In this paper field data are presented on a bifurcation in the Tagliamento River, northeast Italy. The planform configuration of the bifurcation and its temporal evolution was monitored by an automatic digital camera during a series of seven floods with different magnitudes. This remote sensing technique allowed a high temporal resolution (pictures were acquired every hour) that was proved to be essential in a highly dynamic system as the one considered here. Digitized maps of the channels provided information on the location of the bifurcation, the width of the anabranches, the angle between them, along with the occurrence and migration of sediment bars. Data were acquired at two different water levels, giving the possibility to compare low and high flow conditions. The monitored bifurcation is largely unstable and shows sudden changes in the water distribution, mainly driven by the bar migrating in the upstream channel and entering the distributaries. A relationship between width asymmetry and flood magnitude was observed, confirming previous analyses. Moreover, recent theoretical findings were applied, in order to test the possibility to estimate general trends in bifurcation evolution. The analysis pointed out the relevance of a correct assessment of the characteristic temporal scales, as the bifurcation evolves on a timescale similar to that of bar migration and flood duration. Understanding the interactions between these processes is therefore crucial in order to increase the ability to model and predict the morphological evolution of a braided network.
机译：河道分叉是辫状河流中的关键因素，它决定了水和沉积物的分布，从而控制了形态演变。最近的理论和实验发现以及实地观察表明，砾石层辫状河的分岔常常是不对称的，并且高度不稳定。在本文中，现场数据是在意大利东北部的塔格利亚门托河分叉处给出的。分叉的平面形式及其随时间的变化是由一台自动数码相机在一系列七次大小不一的洪水期间进行监测的。这种遥感技术可以实现较高的时间分辨率（每小时获取图像），事实证明，这种高分辨率对于高度动态的系统至关重要。通道的数字化地图提供了有关分叉的位置，分支的宽度，它们之间的角度以及沉积条的发生和迁移的信息。在两个不同的水位采集数据，从而有可能比较低流量和高流量条件。受监控的分叉在很大程度上是不稳定的，并且显示出水分布的突然变化，这主要是由在上游通道中迁移并进入分水器的钢筋驱动的。观察到宽度不对称性和洪水幅度之间的关系，证实了先前的分析。此外，最近的理论发现被应用，以检验估计分叉演化总体趋势的可能性。分析指出了正确评估特征时间尺度的相关性，因为分叉的发展时间与条形迁移和洪水持续时间相似。因此，了解这些过程之间的相互作用对于提高建模和预测编织网络形态演变的能力至关重要。

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