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首页> 外文期刊>Geomorphology >Two pool-to-pool spacing periods on large sand-bed rivers: Mega-pools on the Madeira and Mississippi
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Two pool-to-pool spacing periods on large sand-bed rivers: Mega-pools on the Madeira and Mississippi

机译：在大型沙床河流上有两个池池间隔期：马德拉岛和密西西比河上的巨型池

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The Madeira River thalweg includes two pool-to-pool spacing periods. First, standard pool-crossing sequences form 6 to 8 m deep pools. These pool-crossing sequences recur approximately every six channel widths (9.7 km or 6.8 W), on average. However, the Madeira study reach (between Manicore and Porto Velho in Northern Brazil) is relatively straight, making these pools more frequent than meanders. Second, much deeper pools (13 to 30 m deep) also form at relatively regular, but much longer spacing (50-60 km, about 40 channel widths apart). The deeper "mega-pools" occur where the river reaches the edge of the Holocene alluvium, encountering resistant units (e.g., granite, mud clasts, and conglomerates) in the confining Pleistocene units. These two pool scales also occur on the Lower Mississippi River (downstream of Tarbert Landing). This study identified pool formation processes responsible for these two pool-depth and-spacing scales on two large sand-bed rivers. The analyses computed pool statistics and correlated the deepest pools with planform controls. Two distinct pool formation hypotheses explain the two pool types. The standard pools are "rhythmic" features, developed by macro-turbulent feedbacks, while the mega-pools are "forced" features imposed by the regional geology. The former are fundamentally periodic; the latter are not. However, periodogram analysis indicates that mega-pools on the Madeira form a second, relatively regular pool period. The regional geology, including the confining Pleistocene bluffs and, potentially, orthogonal neotectonic lineaments, imposed periodic regularity to these mega-pools on the Madeira River that is not observed on the Mississippi River, a comparably-sized sand-bed river with mega-pools. (C) 2018 Published by Elsevier B.V.
机译：马德拉河海域包括两个池间间隔期。首先，标准的池越过序列形成6至8 m深的池。平均而言，这些池交叉序列大约每六个通道宽度（9.7 km或6.8 W）重复出现一次。但是，马德拉群岛的研究范围（在巴西北部的Manicore和Porto Velho之间）相对较直，这使得这些水池比蜿蜒的河水更为频繁。第二，更深的水池（13至30 m深）也以相对规则的形式形成，但间隔更长（50-60 km，约40个通道宽度）。较深的“巨型水池”发生在河流到达全新世冲积层边缘的地方，在封闭的更新世单元中遇到了抵抗性单元（例如花岗岩，泥屑和砾岩）。这两个水池规模也发生在密西西比河下游（塔伯特登陆的下游）。这项研究确定了在两条大型沙床河流上负责这两个池深度和间距尺度的池形成过程。分析计算池统计信息，并将最深的池与计划控件相关联。两种不同的池形成假设解释了两种池类型。标准池是由宏观湍流反馈开发的“有节奏”特征，而大型池则是由区域地质施加的“强迫”特征。前者从根本上说是周期性的。后者不是。但是，周期图分析表明，马德拉岛上的大型泳池形成了第二个相对规则的泳池期。包括封闭的更新世虚张声势，以及可能的正交新构造线在内的区域地质，对马德拉河上的这些大型水池施加了周期性规律性，而在密西西比河上却没有观察到这条河。 。 （C）2018由Elsevier B.V.发布

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