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The interaction of buoyant coastal river plumes with mangrove vegetation and consequences for sediment deposition and erosion in a tidal environment
Continental Shelf Research ( IF 2.3 ) Pub Date : 2021-04-22 , DOI: 10.1016/j.csr.2021.104417
Hemanth Vundavilli , Julia C. Mullarney , Iain T. MacDonald , Karin R. Bryan

To identify the drivers of sediment deposition within a mangrove-lined river delta, we developed a three-dimensional numerical model in an idealized domain. Our model system is based on the Firth of Thames, a modern flat-fronted, bay-head deltaic system, in the Hauraki Gulf, in the North Island of New Zealand. The interactions of the buoyant river plume with mangroves are examined, including sediment deposition and erosion patterns. The morphological study presented here is restricted to cohesive sediments, whose patterns are observed after 4 months of morphological evolution. For the non-vegetated case, represented by a spatially uniform roughness, sediment deposited throughout the central model domain with a formation of a cuspate delta at the river mouth. However, in the vegetated case (with vegetated areas represented by an enhanced and spatially varying roughness coefficient), sediment deposition occurred in the regions of forests and flats, whereas the fringe areas experienced erosion. The sediment deposition patterns along cross-sections were qualitatively consistent with field observations from the Firth of Thames. Analysis of the across-transect and along-transect momentum balances demonstrates that the predominant balance between the bottom shear stress and baroclinic pressure gradient largely controls the sediment deposition in the riverine sections of the domain. However, close to the center of the plume, vertical advection promotes suspension of the sediments in the fringe region during the flood tide.



中文翻译:

潮汐环境中沿海浮羽与红树林的相互作用及其对沉积物沉积和侵蚀的影响

为了确定在红树林衬砌的河三角洲内沉积物沉积的驱动力,我们在理想化的领域开发了三维数值模型。我们的模型系统基于泰晤士河峡湾(Firth of Thames),这是一种现代的平地,湾头三角洲系统,位于新西兰北岛的豪拉基湾(Hauraki Gulf)。研究了浮游河羽与红树林之间的相互作用,包括沉积物沉积和侵蚀模式。这里介绍的形态学研究仅限于粘性沉积物,其形态在经过4个月的形态演化后才被观察到。对于非植被的情况,以空间均匀的粗糙度表示,沉积物沉积在整个中央模型域中,并在河口处形成尖齿三角洲。然而,在有植被的情况下(植被面积表示粗糙度系数随空间变化而变化),在森林和平坦地区发生了沉积物沉积,而边缘地区遭受了侵蚀。沿剖面的沉积物沉积模式在质量上与泰晤士河峡湾的实地观察一致。对横断面和沿断面动量平衡的分析表明,底部切应力和斜压梯度之间的主要平衡在很大程度上控制了该地区河道段的沉积物沉积。但是,在羽流中心附近,垂直对流会在洪水潮时促进边缘地区的沉积物悬浮。沉积物沉积发生在森林和平坦地区,而边缘地区遭受侵蚀。沿剖面的沉积物沉积模式在质量上与泰晤士河峡湾的实地观察一致。对横断面和沿断面动量平衡的分析表明,底部切应力和斜压梯度之间的主要平衡在很大程度上控制了该地区河道段的沉积物沉积。但是,在羽流中心附近,垂直对流会在洪水潮时促进边缘地区的沉积物悬浮。沉积物沉积发生在森林和平坦地区,而边缘地区遭受侵蚀。沿剖面的沉积物沉积模式在质量上与泰晤士河峡湾的实地观察一致。对横断面和沿断面动量平衡的分析表明,底部切应力和斜压梯度之间的主要平衡在很大程度上控制了该地区河道段的沉积物沉积。但是,在羽流中心附近,垂直对流会在洪水潮时促进边缘地区的沉积物悬浮。对横断面和沿断面动量平衡的分析表明,底部切应力和斜压梯度之间的主要平衡在很大程度上控制了该地区河道段的沉积物沉积。但是,在羽流中心附近,垂直对流会在洪水潮时促进边缘地区的沉积物悬浮。对横断面和沿断面动量平衡的分析表明,底部切应力和斜压梯度之间的主要平衡在很大程度上控制了该地区河道段的沉积物沉积。但是,在羽流中心附近,垂直对流会在洪水潮时促进边缘地区的沉积物悬浮。

更新日期:2021-04-22
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