The planform mobility of river channel confluences: Insights from analysis of remotely sensed imagery
The planform mobility of river channel confluences: Insights from analysis of remotely sensed imagery
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DOI：
10.1016/j.earscirev.2017.09.009
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发表时间：
2018
影响因子：
12.1
通讯作者：
Simon J. Dixon;Greg . Smith;J. Best;A. Nicholas;J. Bull;M. Vardy;Maminul H. Sarker;S. Goodbred
中科院分区：
文献类型：
--
作者：
Simon J. Dixon;Greg . Smith;J. Best;A. Nicholas;J. Bull;M. Vardy;Maminul H. Sarker;S. Goodbred
河道交汇处被广泛认为是控制水和沉积物下游路线的重要地貌节点，并且是保存覆盖基底冲刷的厚河流沉积物的位置。尽管它们很重要，但对河流交汇处的地层特征或汇流形态动力学在影响地层特征和保存潜力方面的作用的研究却很少。因此，尽管众所周知汇流可以随时间迁移，但汇流地貌学和沉积学模型通常是从汇流保持在固定位置的角度提出的。由于多种原因，这是有问题的，其中最重要的是关于是否可以区分自循环过程（例如合流冲刷）产生的冲刷和由非循环控制驱动的冲刷（例如海平面变化）的持续争论。本文利用 40 年的陆地卫星图像记录来研究河流交汇处的空间流动性，以阐明大型河流交汇处冲刷可能迁移的样式、变化率和面积范围。在这些观察的基础上，提出了汇合冲刷类型的新分类，并将其应用于亚马逊和恒河-布拉马普特拉-梅格纳（GBM）盆地。该分析表明，汇合流动性的驱动因素与更普遍地驱动渠道变化的驱动因素大致相同。因此，在 GBM 盆地中，大量的沉积物供应、季风驱动流量的巨大变化以及容易侵蚀的河岸物质，导致流域内超过 80% 的大型汇流在这 40 年的时间窗口内发生移动；相反，亚马逊流域的这一数字< 40%。这些结果强调：i) 汇流冲刷的潜在面积范围比之前假设的要大得多，贾木纳河（布拉马普特拉河）上的一些汇流位置迁移的距离是支流河道宽度的 20 倍； ii) 汇合位置的广泛迁移比目前假设的更为常见，以及 iii) 汇合流动性通常与决定沉积物产量的流域盆地的岩性和水文特征有关。
River channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment, and which are locations for the preservation of thick fluvial deposits overlying a basal scour. Despite their importance, there has been little study of the stratigraphic characteristics of river junctions, or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential. As a result, although it is known that confluences can migrate through time, models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location. This is problematic for a number of reasons, not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes (such as confluence scour) and that driven by allocyclic controls (such as sea-level change). This paper investigates the spatial mobility of river confluences by using the 40-year record of Landsat Imagery to elucidate the styles, rates of change and areal extent over which large river confluence scours may migrate. On the basis of these observations, a new classification of the types of confluence scour is proposed and applied to the Amazon and Ganges-Brahmaputra-Meghna (GBM) basins. This analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally. Thus in the GBM basin, a high sediment supply, large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80% of large confluences are mobile over this 40-year window; conversely this figure is < 40% for the Amazon basin. These results highlight that: i) the potential areal extent of confluence scours is much greater than previously assumed, with the location of some confluences on the Jamuna (Brahmaputra) River migrating over a distance of 20 times the tributary channel width; ii) extensive migration in the confluence location is more common than currently assumed, and iii) confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield.