Boechat Albernaz Marcio, Roelofs Lonneke, Pierik Harm Jan, Kleinhans Maarten G
Faculty of Geosciences, Department of Physical Geography Utrecht University Princetonlaan 8A Utrecht 3584 CB The Netherlands.
Earth Surf Process Landf. 2020 Dec;45(15):3824-3841. doi: 10.1002/esp.5003. Epub 2020 Oct 1.
Natural levees are common features in river, delta and tidal landscapes. They are elevated near-channel morphological features that determine the connection between channel and floodbasin, and consequently affect long-term evolution up to delta-scales. Despite their relevance in shaping fluvial-tidal systems, research on levees is sparse and often limited to fluvial or non-tidal case studies. There is also a general lack of understanding of the role of vegetation in shaping these geomorphic units, and how levee morphology and dimensions vary in the transition from fluvial to coastal environments, where tides are increasingly important. Our goal is to unravel the effects of fluvial-tidal boundary conditions, sediment supply and vegetation on levee characteristics and floodbasin evolution. These conditions were systematically explored by 60 large-scale idealized morphodynamic simulations in Delft3D which self-developed levees over the course of one century. We compared our results to a global levee dataset compilation of natural levee dimensions. We found that levee height is determined by the maximum water level, provided sufficient levee building sediments are available. Discharge fluctuations increased levee width and triggered more levee breaches, i.e. crevasses, that effectively filled the fluvio-tidal floodbasin. The presence of wood-type (sparse) vegetation further increased the number of crevasses in comparison with the non-vegetated scenarios. Conversely, reed-type (dense) vegetation strongly dampened tidal amplitude and reduced the accommodation space and sedimentation further into the floodbasin, resulting in narrower levees, no crevasses and limited floodbasin accretion. However, dense vegetation reduced tidal forces which allowed levee growth further downstream. Ultimately, the levees merged with the coastal barrier, eliminating the floodbasin tides entirely. Our results elucidate the mechanisms by which levee and crevasse formation, and vegetation may fill fluvio-tidal wetlands and affect estuary evolution. This brings new insights for geological reconstructions as well as for the future management of deltas and estuaries under sea-level rise. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
天然堤是河流、三角洲和潮汐地貌中的常见特征。它们是靠近河道的隆起地貌特征，决定了河道与洪泛盆地之间的联系，从而影响到直至三角洲尺度的长期演化。尽管它们在塑造河潮系统方面具有重要意义，但对天然堤的研究却很稀少，且往往局限于河流或非潮汐的案例研究。人们对植被在塑造这些地貌单元中的作用，以及在潮汐日益重要的从河流环境到海岸环境的过渡过程中天然堤的形态和尺寸如何变化，也普遍缺乏了解。我们的目标是揭示河潮边界条件、沉积物供应和植被对天然堤特征及洪泛盆地演化的影响。通过在Delft3D中进行60次大规模理想化形态动力学模拟，系统地探究了这些条件，这些模拟在一个世纪的时间里自行发育出了天然堤。我们将结果与全球天然堤尺寸数据集汇编进行了比较。我们发现，只要有足够的筑堤沉积物，天然堤的高度就由最高水位决定。流量波动增加了天然堤的宽度，并引发了更多的堤岸决口，即裂缝，这些裂缝有效地填充了河潮洪泛盆地。与无植被的情况相比，木本型（稀疏）植被的存在进一步增加了裂缝的数量。相反，芦苇型（密集）植被强烈地减弱了潮汐振幅，并减少了洪泛盆地深处的容纳空间和沉积，导致天然堤变窄，没有裂缝且洪泛盆地的淤积有限。然而，密集植被减少了潮汐力，这使得天然堤能够在更下游的地方生长。最终，天然堤与海岸屏障合并，完全消除了洪泛盆地的潮汐。我们的结果阐明了天然堤和裂缝形成以及植被可能填充河潮湿地并影响河口演化的机制。这为地质重建以及海平面上升情况下三角洲和河口的未来管理带来了新的见解。© 2020作者。《地表过程与地貌》由约翰·威利父子有限公司出版。
