Downstream fining in contrasting reaches of the sand‐bedded Yellow River
Downstream fining in contrasting reaches of the sand‐bedded Yellow River
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DOI：
10.1002/hyp.8065
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发表时间：
2011-11
影响因子：
3.2
通讯作者：
W. Ta;Haibing Wang;X. Jia
中科院分区：
文献类型：
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作者：
W. Ta;Haibing Wang;X. Jia
与砾石层河流的下游细化相比，几乎没有现场证据支持大型细砂层河流的下游细化过程。事实上，这些河流的典型单峰河床沉积物被认为产生了粗颗粒和细颗粒的相等流动性，这可能会阻碍下游的细化。为了研究这一主题，我们在黄河两个细粒砂层河段（沙漠河段和下游河段）的河床中钻取了200个沉积物岩心，并确定了在3 m厚的河床沉积物中在粗糙的次表层（CSL）上发育的细表层（FSL）。在两个下游河段，FSL的厚度增加，而CSL的厚度减少。对两个河段的CSL和FSL的深度平均中值粒度进行比较，结果表明，CSL的下游细化程度明显依赖于中值粒度，这表明，在600 - 800 km的大尺度上，CSL显示出明显的下游细化，但FSL显示出下游粒度变化没有明显趋势。这一结果表明，来自风载沉积物和跨沙漠支流的细泥沙供应（中值粒径为0.08 mm）可中断FSL并局部粗化河床表面。版权所有© 2011约翰威利父子有限公司.
Compared to downstream fining of a gravel‐bedded river, little field evidence exists to support the process of downstream fining in large, fine sand‐bedded rivers. In fact, the typically unimodal bed sediments of these rivers are thought to produce equal mobility of coarse and fine grains that may discourage downstream fining. To investigate this topic, we drilled 200 sediment cores in the channel beds of two fine‐grained sand‐bedded reaches of the Yellow River (a desert reach and a lower reach) and identified a fine surface layer (FSL) developed over a coarse subsurface layer (CSL) in the 3‐m‐thick bed deposits. In both reaches downstream, the thickness of the FSL increased, while that of the CSL decreased. Comparison of the depth‐averaged median grain sizes of the CSL and the FSL separately in both reaches shows a distinct downstream fining dependence to the median grain size, which indicates that at a large scale of 600‐800 km, the CSL shows a significant downstream fining, but the FSL shows no significant trends in downstream variations in grain size. This result shows that fine sediment supply (0·08 mm median grain size) from wind‐borne sediments and cross‐desert tributaries can interrupt the FSL and coarsen the channel bed surface locally. Copyright © 2011 John Wiley & Sons, Ltd.