Modelling of bed sediment composition changes at the lower shoreface of the Sand Motor
Modelling of bed sediment composition changes at the lower shoreface of the Sand Motor
复制标题
DOI：
10.1016/j.coastaleng.2017.11.007
复制
发表时间：
2018-02-01
影响因子：
4.4
通讯作者：
Stive, M. J. F.
中科院分区：
文献类型：
--
作者：
Huisman, B. J. A.;Ruessink, B. G.;Stive, M. J. F.
海岸线上的大扰动，如荷兰海岸的“沙马达”营养（类似于2100万米(3)），可以引发下海岸海床中位粒度（D-50）的相当大的时空变化。通过数值模型（Delft3D）评估了大规模营养条件下D-50异质性发展的水动力条件的相关性，该模型需要根据2.5年的D-50测量结果进行验证。该方法可以很好地反映所观测到的D-50的空间格局，而不依赖于2DH或3D方法和床层D-50的初始条件。采用了五种沉积物粒度馏分和床层组成的多层管理。床层粗化的程度和幅度与水平潮汐的速度有关，而在高能条件下（即H-mo >= 3 m），粗化的程度要小得多。不同粒径组分之间的不同悬浮行为（它们都在床上被动员起来），导致细粒沉积物（沿海岸方向）优先从较低的岸面（即MSL -6米的向海方向）的沙马达转移。由于所有颗粒的动员和与相对较细的基材混合，风暴条件可能导致粗的顶层部分去除。模拟还表明，细砂组分的输运范围比中砂和粗砂组分深得多。因此，在评估大型海岸结构或土地复垦的环境影响和下滨面沉积物运输时，需要具有多种沉积物组分的模型。
Large perturbations in the coastline, such as the 'Sand Motor' nourishment (similar to 21 million m(3)) at the Holland coast, can initiate considerable spatial and temporal changes in the median grain size (D-50) of the sea bed on the lower shoreface. The relevance of hydrodynamic conditions for the development of the heterogeneity in D-50 at large-scale nourishments was assessed with a numerical model (Delft3D), which required a validation against 2.5 years of D-50 measurements. A good representation of the observed spatial pattern of D-50 was obtained independent of a 2DH or 3D approach and initial condition for the D-50 of the bed. Five sediment size fractions and a multi-layer administration of the bed composition were used. The extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide, while a far less pronounced coarsening takes place during energetic conditions (i.e. H-mo >= 3 m). Differential suspension behaviour between the size fractions, which are all mobilized at the bed, causes a preferential transport of fine sediment (in alongshore direction) away from the Sand Motor at the lower shoreface (i.e. seaward of MSL -6 m). Storm conditions may induce a partial removal of the coarse top-layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material. Simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions. Models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large-scale coastal structures or land reclamation's and sediment transport on the lower shoreface.