Modeling long-term delta dynamics reveals persistent geometric river avulsion locations
Modeling long-term delta dynamics reveals persistent geometric river avulsion locations
复制标题
DOI：
10.1016/j.epsl.2021.116786
复制
发表时间：
2021-04
影响因子：
5.3
通讯作者：
K. Ratliff;E. Hutton;A. Murray
中科院分区：
文献类型：
--
作者：
K. Ratliff;E. Hutton;A. Murray
河流三角洲是通过沉积岩瓣的反复叠加而形成的，其位置和大小由河道撕脱（河道的相对突然变化）决定。我们使用一个模型耦合河流和海岸过程，探索撕脱动力学的波能量和海平面上升率的范围内，并发现在我们的模型中的撕脱位置和三角洲瓣大小的主要控制是临界超高比（SER），相对于周围的河漫滩，需要触发撕脱的通道淤积量。首选的撕脱位置出现，因为几何约束-一个优先的撕脱节点发生在河漫滩斜坡，开发作为河流的洪水和/或海平面上升的突破。在我们的模型中，这是因为河流剖面通过线性扩散进行加积和侵蚀，而洪泛区地形的扩散仅限于幕式决口展布。这些结果是在最近的建模工作，这是出于实验室实验，并假设一个联盟之间的河道和河漫滩淤积率，并在撕脱节点的回水水动力驱动。在我们的模型中，首选的撕脱长度与实验室、现场和模型结果（不包括水动力回水效应）具有良好的比例关系。这项工作提出了一种替代机制来解释撕脱位置的三角洲洪泛区地形加格拉德和/或扩散比河道剖面更慢，它指出需要阐明河道和洪泛区连接在大的空间和时间尺度，以及如何连接不同的三角洲从一种类型到另一种。
River deltas grow through repeated stacking of sedimentary lobes, the location and size of which are determined by channel avulsions (relatively sudden changes in river course). We use a model coupling fluvial and coastal processes to explore avulsion dynamics under a range of wave energies and sea-level-rise rates and find that the primary control on avulsion location and delta lobe size in our model is the critical superelevation ratio (SER), the amount of channel aggradation relative to the surrounding floodplain that is required to trigger an avulsion. The preferred avulsion location arises because of geometric constraints – a preferential avulsion node occurs at the break in floodplain slope that develops as the river progrades and/or sea level rises. This concavity develops in our model because the river profile aggrades and erodes via linear diffusion, whereas the diffusion of the floodplain topography is limited to episodic crevasse splays. These results are in contrast to recent modeling work, which was motivated by laboratory experiments and assumes a union between river channel and floodplain aggradation rates, and where avulsion nodes are driven by backwater hydrodynamics. The preferred avulsion length in our model scales well with laboratory, field, and model results without including hydrodynamic backwater effects. This work suggests an alternative mechanism to explain avulsion locations on deltas where floodplain topography aggrades and/or diffuses more slowly than the river channel profile, and it points to the need to elucidate river channel and floodplain connectivity over large space and time scales, and how the connectivity varies from one type of delta to another.