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Paleodischarge reconstruction using oxbow lake sediments complicated by shifting hydrological connectivity
Quaternary International ( IF 2.2 ) Pub Date : 2021-07-08 , DOI: 10.1016/j.quaint.2021.07.004
Zhixiong Shen 1 , Molly Aeschliman 1 , Nicholas Conway 1
Affiliation  

Alluvial sedimentary records attract great attention for quantitative paleoflood studies because they may preserve continuous high-resolution archives in lowland floodplains that are most vulnerable to inland flooding. The coarse-grained flood deposit in oxbow lakes emerges as a promising paleoflood proxy due to its sensitivity to flood magnitude and high preservation potential. Previous work has established a coarseness-discharge correlation for the instrumental period that was subsequently used to retrodict paleodischarge of older flood deposits. However, it has not been tested whether this correlation applies to older deposits that may represent different lake hydrological connectivity due to plug-bar growth and river migration. Furthermore, overbank sedimentation is known to be episodic and may not scale with flood magnitude. Here we investigate this issue by comparing peak annual discharge and the coarseness of a two-stage infill sequence of a ~60 yr old oxbow lake in South Carolina, USA. We found that local morphology had the first-order control and was responsible for the sedimentation shift in the lake. There is a strong linear coarseness-discharge correlation in the upper section of the lake infill. However, this correlation overestimated the flood magnitude for flood deposits in the lower section. This finding suggests that oxbow lake sediments can be greatly useful for paleoflood reconstruction, but this may be complicated by shifting hydrological connectivity. Therefore, the stratigraphic context of an oxbow lake needs to be well understood to derive paleodischarge from the sediments properly.



中文翻译:

牛轭湖沉积物与水文连通性变化复杂的古排水重建

冲积沉积记录引起了定量古洪水研究的极大关注,因为它们可以在最容易受到内陆洪水影响的低地漫滩中保存连续的高分辨率档案。牛轭湖中的粗粒洪水沉积物因其对洪水规模的敏感性和高保存潜力而成为有希望的古洪水代理。先前的工作已经建立了仪器时期的粗度-流量相关性,随后用于追溯旧洪水沉积物的古流量。然而,尚未测试这种相关性是否适用于可能代表不同湖泊水文连通性的较旧沉积物,这些沉积物可能因塞杆生长和河流迁移而产生不同的湖泊水文连通性。此外,众所周知,河岸上的沉积是偶发性的,可能不会随着洪水的大小而变化。在这里,我们通过比较美国南卡罗来纳州一个约 60 年历史的牛轭湖的年流量峰值和两阶段填充序列的粗糙度来研究这个问题。我们发现局部形态具有一级控制作用,是造成湖泊沉积变化的原因。在湖泊填充物的上部有很强的线性粗度-流量相关性。然而,这种相关性高估了下部洪水沉积物的洪水规模。这一发现表明牛轭湖沉积物对古洪水重建非常有用,但这可能会因水文连通性的变化而变得复杂。因此,需要很好地了解牛轭湖的地层背景,才能正确地从沉积物中获得古排放。

更新日期:2021-07-08
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