Rivers in reverse: Upstream-migrating dechannelization and flooding cause avulsions on fluvial fans
Rivers in reverse: Upstream-migrating dechannelization and flooding cause avulsions on fluvial fans
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DOI：
10.1130/g49318.1
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发表时间：
2022-01-01
期刊：
影响因子：
5.8
通讯作者：
Hajek, Elizabeth A.
中科院分区：
文献类型：
--
作者：
Edmonds, Douglas A.;Martin, Harrison K.;Hajek, Elizabeth A.
河流的崩解作用形成了洪泛平原，填满了冲积盆地。我们报告了陆地卫星记录中发现的一种新型河流崩裂。我们在安第斯和新几内亚冲积盆地茂密的河流扇上发现了69个逆冲冲蚀例子。退行性冲刷是由河道堵塞引起的，例如淤塞，淤塞使泥沙填满河道，迫使水流过岸（去河道化），从而形成一个字形的洪泛格局。去信道化波以387米/年的中位数速率向上游传播，平均持续13年；许多河流在同一河段表现出多次去渠道化事件。当河流找到一条新的流道时，去通道化结束，崩解完成。我们用一个一维形态动力学模型模拟明渠流动的上游迁移去通道化。观测结果与模式结果一致，并表明在陡峭（10（-2）至10(-3)）、低流量(类似于10(1)米（3)秒（-1））的河流上，河道阻塞会导致去通道化。这说明了在生态学和地层学模型中没有考虑到的一种新的洪泛区沉积类型。
The process of river avulsion builds floodplains and fills alluvial basins. We report on a new style of river avulsion identified in the Landsat satellite record. We found 69 examples of retrogradational avulsions on rivers of densely forested fluvial fans in the Andean and New Guinean alluvial basins. Retrogradational avulsions are initiated by a channel blockage, e.g., a logjam, that fills the channel with sediment and forces water overbank (dechannelization), which creates a chevron-shaped flooding pattern. Dechannelization waves travel upstream at a median rate of 387 m/yr and last on average for 13 yr; many rivers show multiple dechannelizing events on the same reach. Dechannelization ends and the avulsion is complete when the river finds a new flow path. We simulate upstream migrating dechannelization with a one-dimensional morphodynamic model for open channel flow. Observations are consistent with model results and show that channel blockages can cause dechannelization on steep (10(-2) to 10(-3)), low-discharge (similar to 10(1) m(3) s(-1)) rivers. This illustrates a new style of floodplain sedimentation that is unaccounted for in ecologic and stratigraphic models.