Hydrology of Braided River Systems

[20755 . 56]福富拉河是一个复杂的动力系统，由多个不稳定的冲积河道组成，这些河道在沙洲和岛屿周围分裂和重新接合，并频繁地在河流的辫状平原上迁移。辫状河在低洼地区并不常见，但在高纬度地区和快速沉积地区占主导地位。在阿拉斯加和太平洋西北部等地区，它们代表着一个重大的管理挑战，因为在这些地区必须修建桥梁和管道。此外，辫状河冲积层是水、油、气、煤、砂、砾石和重矿物的重要储集层。它们的不稳定性和随机流动模式使得预测辫状河极其困难。最近的进展提出了几种分析这些复杂动力系统的新方法。现在很清楚，辫状河表现出空间和动态（时空）尺度；即，在适当的复封条件下，河网的一小部分在平台几何形状和演变方面与大部分在统计上相似。这一观察结果为统计预测罕见的、高震级的通道移动提供了可能性，这些变化可以从容易获得的较小尺度上发生的较低震级但更频繁的事件的记录中得到。同样清楚的是，至少有一些系统尺度或辫状河的“涌现”特性可以根据河流动力学的简化模型来预测。最后，最近的实验工作表明，适度的河岸植被可以显著影响辫状河的平台格局和动态；甚至有可能仅仅通过植被效应就把一条辫状河变成曲流河。在此基础上，我们建议将这三方面的研究结合起来，重点关注以下基本问题：(1)将辫状河的尺度分析扩展到第三（垂直）维度，即流量、速度、河床高程和泥沙通量的尺度分析，为现代河流的洪水、冲刷和流动以及古代沉积物的地层结构的统计预测提供依据；(2)利用水文比例尺结果作为模型度量，对现有辫状河模型进行检验和改进；(3)研究植被对辫状河的影响，重点关注水流和植被的重复循环如何导致辫状河的水流“规格化”，进入少数明确的河道，打破尺度，并可能导致第一次真正自我再生的曲流的发展。

0207556FoufoulaBraided rivers are complex dynamical systems comprising multiple unstable alluvial channels that divide and rejoin around bars and islands and migrate frequently across the river's braidplain. Although not common in lowland areas, braided rivers are dominant at high latitudes and in areas with rapid sedimentation. They represent a major management challenge in areas such as Alaska and the Pacific Northwest where bridges and pipelines must be built across them. In addition, the alluvial deposits of braided rivers are important reservoirs of water, oil, gas, coal, sand, gravel and heavy minerals. Their instability and opportunistic flow patterns make prediction of braided rivers extremely difficult.Recent advances have suggested several new ways of analyzing these complex dynamical systems. It is now clear that braided rivers exhibit both spatial and dynamic (time-space) scaling; i.e. a small part of the river network is statistically similar to a larger part, in terms of planform geometry and evolution, under appropriate resealing. This observation opens up the possibility of statistical prediction of rare, high-magnitude channel shifts from readily obtainable records of lower magnitude but more frequent events occurring at smaller scales. It is also clear that at least some of these system-scaling or "emergent" properties of braided rivers can be predicted on the basis of simplified models of the stream dynamics. Finally, recent experimental work has illustrated that the planform pattern and dynamics of braided rivers can be dramatically affected by modest amounts of bank vegetation; it may even be possible to convert a braided to meandering river by vegetation effects alone.We propose to unite and build on these three lines of research, focusing on the following basic issues: (1) extension of scaling analysis in braided rivers to the third (vertical) dimension, i.e., scaling of flows, velocities, bed elevation and sediment flux, with implications for statistical prediction of floods, scour and mobility in modern rivers, and stratigraphic architecture in ancient deposits; (2) testing and refinement of existing braided-river models using hydrologic scaling results as a model metric; and (3) study of the effects of vegetation on braided rivers, focusing on how repeated cycles of flow and vegetation can lead to the 'regularization' of braided-river flows into a small number of well defined channels, breaking the scaling and perhaps leading to the development of the first truly self-regenerating meanders.