Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions
Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions
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DOI：
10.1016/j.geomorph.2018.04.016
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发表时间：
2018-08
期刊：
影响因子：
3.9
通讯作者：
I. D. Lichtman;J. Baas;L. Amoudry;P. Thorne;J. Malarkey;J. Hope;J. Peakall;D. Paterson;S. Bass;R. Cooke;A. Manning;A. Davies;D. Parsons;L. Ye
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文献类型：
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作者：
I. D. Lichtman;J. Baas;L. Amoudry;P. Thorne;J. Malarkey;J. Hope;J. Peakall;D. Paterson;S. Bass;R. Cooke;A. Manning;A. Davies;D. Parsons;L. Ye
许多海岸和河口环境主要由非粘性沙和粘性泥混合而成。在这些环境中，波纹和沙丘等底床的运移速率对于确定底质运移速率、告知和评估泥沙运移和地貌的数值模型很重要。然而，这些模型往往忽略描述天然混合沉积物中物理和生物凝聚力(由粘土和胞外聚合物(EPS)产生)的参数，这主要是因为缺乏相关的实验室和现场数据。为解决这一认识上的差距，在春季-小潮周期收集了潮间带滩涂的数据，以确定具有生物活性的混合沙泥中床型的床料输移率。随着潮汐从春季向小潮推进，床层粘性成分从低于2 Vol%变化到5.4 Vol%粘性粘土。底泥中EPS的含量与粘粒含量呈线性关系。通过多元线性回归，发现输沙率依赖于Shields应力参数和床层粘性粘土含量。当粘性粘土和聚苯硫醚含量分别低于2.8 Vol%和0.0 5 wt%时，迁移速率随粘性粘土和聚苯乙烯含量的增加而降低。超过这些界限，研究区域内的仪器无法检测到床形迁移和床料运移。这些限制与最近进行的沙-粘土和沙-EPS平台发育实验室实验是一致的。这项工作对于在混合砂土环境中应用现有的纯砂床状运移公式的情况具有重要意义，特别是因为2.8%Vol%的粘性粘土完全符合通常采用的“干净砂”的定义。
Many coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 vol% up to 5.4 vol% cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 wt%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of “clean sand”.