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Long-term morphodynamics of a large estuary subject to decreasing sediment supply and sea level rise
Global and Planetary Change ( IF 3.9 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.gloplacha.2020.103212
Bing Yuan , Jian Sun , Binliang Lin , Fanyi Zhang

Abstract Globally the sediment supply from rivers to estuaries is decreasing and the mean sea level is rising, while the effects of these changes on the long-term estuarine morphodynamics have not been fully explored. An idealized one-dimensional model was utilized to investigate the long-term morphodynamics of a large estuary subject to the changes in the sediment supply and sea level. Simplifications involved the use of a 560 km long funnel-shaped channel with fixed banks, constant input water and sediment fluxes, a single grain size and a semi-diurnal tide. A range of values of changes in the sediment supply (50–90% reduction) and sea level (1–5 mm/yr increase) were considered. Starting from an equilibrium state for an initial sediment supply, the estuary shifts to a new equilibrium for the considered changes. The shift is completed on a timescale of millennia, while 50% of the bed level change occurs within several hundreds of years. A larger decrease in the sediment supply results in a stronger bed erosion, while the corresponding adjustment time has minor changes in its range for the considered sediment reduction. In addition to the reduced sediment supply, under sea level rise the erosion is weakened and the adjustment time is shortened. The equilibrium under the considered rates of sea level rise is characterized by a bed level keeping pace with the sea level and a significant amount of sediment being trapped in the estuary. Additional numerical experiments that use the real geometry and more realistic forcing of the Yangtze Estuary show that overall erosion of the estuary is expected in the coming centuries.

中文翻译:

受沉积物供应减少和海平面上升影响的大型河口的长期形态动力学

摘要 在全球范围内,河流向河口的沉积物供应量在减少,平均海平面在上升,而这些变化对河口长期形态动力学的影响尚未得到充分探讨。利用理想化的一维模型来研究受沉积物供应和海平面变化影响的大型河口的长期形态动力学。简化包括使用 560 公里长的漏斗形渠道,固定堤岸、恒定输入水和沉积物通量、单一粒度和半日潮。考虑了沉积物供应(减少 50-90%)和海平面(每年增加 1-5 毫米)的一系列变化值。从初始沉积物供应的平衡状态开始,河口转变为考虑到的变化的新平衡。这种转变是在数千年的时间尺度内完成的,而 50% 的床位变化发生在数百年内。输沙量减少幅度越大,河床侵蚀越强烈,而相应的调整时间在其考虑的减沙量范围内变化较小。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。而50%的床位变化发生在数百年内。输沙量减少幅度越大,河床侵蚀越强烈,而相应的调整时间在其考虑的减沙量范围内变化较小。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。而50%的床位变化发生在数百年内。输沙量减少幅度越大,河床侵蚀越强烈,而相应的调整时间在其考虑的减沙量范围内变化较小。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。输沙量减少幅度越大,河床侵蚀越强烈,而相应的调整时间在其考虑的减沙量范围内变化较小。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。输沙量减少幅度越大,河床侵蚀越强烈,而相应的调整时间在其考虑的减沙量范围内变化较小。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。除了泥沙供应减少外,海平面上升时侵蚀减弱,调整时间缩短。在所考虑的海平面上升速率下,平衡的特点是河床水平与海平面同步,大量沉积物被困在河口。使用真实几何学和更真实的长江口强迫的其他数值实验表明,预计在未来几个世纪,河口将被整体侵蚀。
更新日期:2020-08-01
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