Net beach change in the swash zone: A numerical investigation
Net beach change in the swash zone: A numerical investigation
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DOI：
10.1016/j.advwatres.2012.10.002
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发表时间：
2013-03
影响因子：
4.7
通讯作者：
Fangfang Zhu;N. Dodd
中科院分区：
文献类型：
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作者：
Fangfang Zhu;N. Dodd
一系列推移质输沙公式被用来对可侵蚀的平面海滩上的一个冲刷周期进行完全耦合的地貌动力学模拟。求解了一个由浅水方程和Exner方程组成的系统，其中输沙率Q要么仅取决于深度平均流速u，要么取决于u和水深h。计算结果与等效解耦结果[2]是一致的，因为所考虑的所有输沙公式都适用于[1]事件，在整个泥沙流中产生净侵蚀。然而，与[3]一致的是，对于所有的Q=Q(U)公式，完全耦合比同等的非耦合结果产生的侵蚀要小得多。结果表明，非耦合方法和耦合方法(对于大多数公式)之间的差异在SWASH事件的过程中逐渐累积。净侵蚀量减少的主要原因是最大洪水较小。结果还表明，在全耦合模拟的推移质输沙公式中加入对h的依赖关系，可能会导致上冲刷的净淤积。由Chezy定律描述的河床剪应力被进一步包括在全耦合模拟中，以检查净海滩的变化。对于Q=Q(U)和Q=Q(h，u)，预测的最大淹没和净近海泥沙输运都将大大减少。结果表明，虽然在一次激流事件下，冲刷底部的净泥沙通量仍在近海，但当考虑床面剪切力时，特别是当反冲阻力系数比上涌阻力系数减小时，可以预测中、上冲刷的泥沙淤积，这与一些现场测量结果一致。这意味着，不仅为了获得正确的定量海滩变化，而且为了获得正确的海滩性质，必须包括床面剪应力。
A range of bed-load sediment transport formulae are used to run fully coupled, morphodynamic simulations of one [1] swash cycle on an erodible plane beach. A system comprising shallow water equations and Exner equation is solved, in which sediment transport rate q is either dependent only on depth averaged velocity (u), or on u and water depth (h). The results are in agreement with equivalent uncoupled results [2] in that all sediment transport formulae considered applied to the event of [1] yield net erosion in the whole of the swash. Consistent with [3], however, full coupling yields significantly less erosion for all the q=q(u) formulae compared to the equivalent uncoupled results. It is shown that differences between uncoupled and coupled approaches (for most formulae) accumulate over the course of the swash event. The main reason for the reduced net erosion is the smaller maximum inundation. It is also shown that including a dependence on h in the bed load sediment transport formula for fully coupled simulations can result in net deposition in the upper swash. Bed shear stress described by a Chezy law is further included in fully coupled simulations to examine net beach change. Much reduced maximum inundation and net offshore sediment transport are predicted both for q=q(u) and q=q(h,u). It is shown that although the net sediment flux at the base of the swash under one [1] swash event is still offshore, deposition in the middle or upper swash may be predicted when bed shear stress is included, particularly when the drag coefficient in the backwash is reduced compared to that in the uprush, consistent with some in-situ measurements. The implication is that bed shear stress must be included not just to obtain correct quantitative beach change, but also to obtain correct qualitative beach behaviour.