Assessing Channel Bank-Height Adjustments and Flood Frequency Trends in a Dynamic Channel-Levee Evolution Model

IF 3.5 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
J. Han, W. Kim, D. A. Edmonds
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引用次数: 0

Abstract

Natural levees form through sediment delivery from channels, dispersal onto floodplains, and storage at channel margins. When levees breach, they release water and sediment onto the floodplain, occasionally causing river avulsions. Despite their significance, levee growth remains poorly understood, and no existing models capture the dynamic channel-levee evolution systems. A common assumption is that levee and channel bed aggradation rates are coupled or equal; however, this cannot be true because levees do not accumulate everywhere along aggrading channel belts. Using a one-dimensional numerical model, we investigate levee growth decoupled from channel bed aggradation under flood scenarios wherein the flooded level: (a) exceeds the levee crest height (i.e., front loading); or (b) is lower than the levee crest partially inundating distal levee deposits (i.e., back loading). Front loading events initially aggrade the levee crest, which confines the channel, increases bankfull depth, and reduces flooding. During confinement, levee growth restricts flooding, and minor back loading events are more common. Over this period, the channel bed aggrades until bankfull depth decreases sufficiently to trigger larger floods. This channel-releasing process increases flood likelihood and enhances overbank accumulation, promoting front loading and re-confining the channel. Our findings suggest aggradational channels may experience confined-release phases characterized by episodic levee growth and fluctuating bankfull depth. Rapid in-channel aggradation increases flood frequency and variability with more confined-release cycles. These results imply that river avulsions and associated floods might preferentially occur when the channel bed aggrades faster than adjacent levees, whereby the channel becomes shallower and destabilized.

Abstract Image

动态河道-堤防演化模型中河道堤岸高度调整和洪水频率趋势的评估
天然堤防是通过泥沙从河道输送、扩散到洪泛区以及在河道边缘的储存而形成的。当堤坝决口时,它们会将水和沉积物释放到洪泛区,偶尔会造成河流冲刷。尽管它们具有重要意义,但对堤防增长的了解仍然很少,而且没有现有的模型能够捕捉到动态河道-堤防演化系统。一个常见的假设是堤防和河床的沉积速率是耦合或相等的;然而,这是不可能的,因为堤防并不是沿着河道淤积带到处堆积的。利用一维数值模型,我们研究了洪涝水位(a)超过洪峰高度(即前荷载)的情况下堤防生长与河床淤积解耦的情况;或(b)低于部分淹没远端堤防沉积物的堤顶(即反向荷载)。前荷载事件最初使堤防波峰淤积,从而限制了河道,增加了堤岸深度,减少了洪水。在约束期间,堤坝的增长限制了洪水,较小的反加载事件更为常见。在此期间,河床会不断淤积,直到堤岸深度下降到足以引发更大的洪水。这一河道释放过程增加了洪水发生的可能性,并增加了河岸上的堆积,促进了河道的前部负荷和重新限制。我们的研究结果表明,沉积河道可能经历以偶发性堤防增长和岸深波动为特征的受限释放阶段。河道内的快速淤积增加了洪水的频率和变异性,并增加了更多的限制释放循环。这些结果表明,当河床比相邻堤防沉降更快时,河道会变得更浅和不稳定,河流冲刷和相关洪水可能优先发生。
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来源期刊
Journal of Geophysical Research: Earth Surface
Journal of Geophysical Research: Earth Surface Earth and Planetary Sciences-Earth-Surface Processes
CiteScore
6.30
自引率
10.30%
发文量
162
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