决口扇沉积物发育过程中的水槽实验:从不对称几何形状到对称几何形状的转变

IF 2 4区 地球科学 Q1 GEOLOGY
Taichi Kato, Masaki Yamada, H. Naruse, Sakai Yuichi
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引用次数: 0

摘要

决口扇沉积物在重建过去洪水事件的规模和了解河流系统的行为方面发挥着重要作用。尽管对决口扇沉积物的几何形状和相进行了广泛的研究,但对其时空发育过程仍知之甚少。本研究采用比例水槽试验,研究决口扇发育过程与其特征之间的关系。在水槽中设置了一个实验水槽,以模拟2019年日本中部千驹河洪水。为了模拟跨岸水流,在水槽壁的一侧创建了一个开口,水流通过该开口淹没在水平丙烯酸板上。实验中使用的沉积物由粒度约为0.3和0.1毫米的颗粒组成,通过尺寸分析确定这些颗粒相当于真实规模河流中的推移质砾石和悬浮沙。实验结果揭示了三个重要发现:(1)决口扇沉积物最初在主河道下游形成不对称形状,但逐渐呈现对称几何形状。河流主流最初影响淹没水流的方向,但沉积物堆积后的河道分叉后来将八字的几何形状改变为更对称的形状。(2) 决口扇沉积物发育在两个不同的区域(近端和远端扇),分别对应于推移质和悬移质的沉积物输送。这两个区域通常在实际场尺度中观察到。(3) 最初的跨岸流是一种没有通道的片状流,这导致粗粒沉积物分布在广阔的区域。随后,发育河道内部的粗砂堆积导致近端扇上游的细粒沉积物堆积。因此,近端扇沉积物在下游变得稍微粗糙,而在与远端扇的边界处则迅速变细。这些发现表明,决口扇沉积的特征随地形发育阶段的不同而不同,从而为解释其沉积相提供了依据。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Flume experiments in the development of crevasse-splay deposits: transition from asymmetric-to-symmetric geometry
Crevasse-splay deposits play an important role in the reconstruction of the magnitude of past flood events and in understanding the behavior of river systems. Despite the extensive studies conducted on the geometry and facies of crevasse-splay deposits, their spatiotemporal developmental processes have remained insufficiently understood. In this study, scaled flume experiments were conducted to study the relationship between the developmental processes of crevasse splays and their characteristics. An experimental flume was set up in a tank to simulate the 2019 Chikuma River flood, Central Japan event. To model the overbank flow, an opening was created on the side of the flume’s wall through which the flow flooded onto a horizontal acrylic plate. The sediment used in the experiments consisted of particles with grain sizes of approximately 0.3 and 0.1 mm, which were determined to be equivalent to bedload gravel and suspended sand in a real-scale river using dimensional analysis. The results of the experi ments revealed three important findings: (1) Crevasse-splay deposits initially developed an asymmetric shape extending downstream of the main river channel but gradually showed a symmetric geometry. The river mainstream initially influenced the direction of the inundation flow, but channel bifurcations after the deposition of the sediment piles later changed the geometry of splays into a more symmetric shape. (2) Crevasse-splay deposits developed in two distinct regions (proximal and distal splay), corresponding to sediment transport by bedload and suspended load, respectively. These two regions are commonly observed in the actual field scale. (3) The original overbank flow was a sheet flow without channels, which caused coarse-grained sediments to be spread over a wide area. Subsequently, the accumulation of coarse sands in the developed channel interiors resulted in the buildup of finer-grained sediments upstream of the proximal splay. Thus, the proximal splay deposits became slightly coarse downstream, whereas they rapidly became fine at the boundary with the distal splay. These findings indicate that the characteristics of crevasse-splay deposits vary with the landform’s development stage, thus providing a basis for interpreting their depositional facies.
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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