Field observations of wave-averaged suspended sediment concentrations in the inner surf zone with varying storm conditions

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Marine Geology Pub Date : 2024-05-04 DOI:10.1016/j.margeo.2024.107302
P.P.J. van Wiechen, S. de Vries, A.J.H.M. Reniers
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Abstract

During extreme conditions, the transport of the wave-averaged suspended sediment concentrations in the inner surf zone affects dune erosion. Although large-scale laboratory experiments have provided insight in what drives these sediment concentrations, corresponding field data are lacking. To fill this gap, novel field observations of suspended sediment concentrations are compared to drivers that govern sediment suspension during storm conditions known from literature. A total of 128 time intervals of 20 min are analysed, spread over 10 different high water events with different hydrodynamic conditions. For each time interval, the wave-averaged (i.e. 20 min mean) suspended sediment concentration is computed and compared to three suspension drivers. The studied drivers are (1) bed shear due to near bed velocities that originate from mean currents in combination with wave-induced orbital flow, (2) the horizontal pressure gradients under steep wave fronts that increase the forces on the bed material, and (3) bore-induced turbulence that is generated at the free surface and reaches the bed. The derived bore-induced turbulence generates the greatest correlation with the mean suspended sediment concentrations (r = 0.74, p = 4.47E-23). Samples that deviate from this correlation correspond to time intervals with lower values of derived bore turbulence, less wave energy saturation in the inner surf zone, and stronger mean currents. The correlation with the mean suspended sediment concentrations increases when the shear stress originating from mean currents is used for these time intervals (r = 0.83, p = 1.63E-33). For time intervals during which more energetic conditions persist and the wave energy is saturated in the nearshore, bore turbulence was the dominant mechanism in stirring up sediment. The outcome of this study suggests that, based on the events analysed, dune erosion models may achieve more accurate results if computations of suspended sediment concentrations include a bore-induced turbulence term, or if already included, properly address the relative importance of bore-induced turbulence when compared to bed shearing.

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对不同风暴条件下内冲浪区海浪平均悬浮沉积物浓度的实地观测
在极端条件下,波浪平均悬浮沉积物浓度在内侧冲浪区的传输会影响沙丘侵蚀。虽然大规模的实验室实验已经让人们了解了这些沉积物浓度的驱动因素,但却缺乏相应的实地数据。为了填补这一空白,我们将对悬浮沉积物浓度的新实地观测结果与文献中已知的风暴条件下控制沉积物悬浮的驱动因素进行了比较。共分析了 128 个 20 分钟的时间间隔,这些时间间隔分布在 10 个具有不同水动力条件的不同涨水事件中。在每个时间间隔内,计算波浪平均值(即 20 分钟平均值)的悬浮泥沙浓度,并与三种悬浮驱动因素进行比较。所研究的驱动因素包括:(1) 源自平均水流的近床速度与波浪诱发的轨道流相结合产生的床面剪切力;(2) 陡峭波浪前沿下的水平压力梯度增加了对床面材料的作用力;(3) 在自由表面产生并到达床面的孔隙诱发湍流。得出的钻孔诱导湍流与平均悬浮沉积物浓度的相关性最大(r = 0.74,p = 4.47E-23)。偏离这一相关性的样本对应于导出孔湍流值较低的时间段、内冲浪区波浪能量饱和度较低以及平均海流较强的时间段。如果在这些时间段使用平均海流产生的剪应力,则与平均悬浮沉积物浓度的相关性会增加(r = 0.83,p = 1.63E-33)。在近岸持续存在较强能量条件且波浪能量饱和的时间段,钻孔湍流是搅动沉积物的主要机制。这项研究结果表明,根据所分析的事件,如果在计算悬浮沉积物浓度时加入钻孔引起的湍流项,或者如果已经加入钻孔引起的湍流项,则适当考虑钻孔引起的湍流与床面剪切相比的相对重要性,沙丘侵蚀模型可能会获得更准确的结果。
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来源期刊
Marine Geology
Marine Geology 地学-地球科学综合
CiteScore
6.10
自引率
6.90%
发文量
175
审稿时长
21.9 weeks
期刊介绍: Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.
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