Morphodynamic evolution of experimental cohesive deltas
Morphodynamic evolution of experimental cohesive deltas
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DOI：
10.1029/2007jf000882
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发表时间：
2009-04-23
影响因子：
3.9
通讯作者：
Sheets, B. A.
中科院分区：
文献类型：
--
作者：
Hoyal, D. C. J. D.;Sheets, B. A.
在这里，我们描述了在实验室中创建河流为主的（鸟足）三角洲强通道化的新技术。实现强自通道化的关键是向沉积物混合物中添加市售聚合物。这种聚合物增强了基底强度，增加了临界侵蚀应力，这是一个重要的地貌阈值。更重要的是，它增加了凝聚力的发生率，以解释在小规模实验中形态动力学演化的增加率。三角洲演化的周期模式。三角洲的“撕脱循环”始于河道撕脱、侵蚀和河道延长，而结束于河道萎缩和废弃。这个循环似乎是普遍的，但受到一系列的控制，包括沉积物粒度分布，沉积物浓度，衬底的凝聚力，弗劳德数。我们建议，所观察到的沉积周期的特征是一个撕脱机制，比目前的模型的河流系统，一般解释撕脱概率作为上游效应依赖于渠道超高或堤坝坡度更复杂。实验表明，在许多分流河道系统，包括三角洲，冲积，深水扇，下游介导的地形效应或“形态动力回水效应”可能会主导上游撕脱过程和控制表面力学和地层。实验观察合成到一个新的沉积模型，强调自组织和反馈的重要性，在三角洲表面的演变和地层的河流为主的三角洲。
Here we describe new techniques for creating river-dominated (birds foot) deltas with strong channelization in the laboratory. The key to achieving strong self-channelization is the addition of a commercially available polymer to the sediment mixture. This polymer enhances the substrate strength increasing the critical erosion stress, an important geomorphic threshold. More importantly it increases the rate of cohesion onset to account for increased rates of morphodynamic evolution in small-scale experiments. A cyclic pattern of delta evolution is observed. The delta "avulsion cycle'' begins with channel avulsion, erosion, and channel elongation and ends with channel backfilling and abandonment. This cycle appears to be universal but is subject to a range of controls, including sediment size distribution, sediment concentration, substrate cohesiveness, and Froude number. We propose that the observed depositional cycle is characteristic of an avulsion mechanism that is more complex than current models of fluvial systems, which generally explain avulsion probability as an upstream effect dependent on channel superelevation or levee slope. The experiments suggest that in many distributary channel systems, including deltas, alluvial, and deep water fans, downstream mediated topographic effects or "morphodynamic backwater effects'' may dominate over upstream avulsion processes and control the surface mechanics and stratigraphy. The experimental observations are synthesized into a new depositional model for river-dominated deltas which emphasizes the importance of self-organization and feedback in delta surface evolution and stratigraphy.