Collaborative Research: Observation and Modeling of Inner Shelf Sediment Dynamics and Large-Scale Sorting: Cross-shelf or Alongshelf Transport?

合作研究：内陆架沉积物动力学观测和建模以及大规模分选：跨架还是沿架运输？

• 批准号: 0452178
• 负责人: Brad Murray
• 金额: $ 15.28万
• 依托单位: Duke University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0452178&HistoricalAwards=false
• 关键词: Collaborative; Research; Observation; Modeling; Inner

Under this award the PIs will investigate the origin and significance of rippled scourdepressions or sorted bedforms. These are found on the inner continental shelves in relatively coarse sediment, which extend kms in the cross-shore direction and are on the order of 100 m wide. Previously these have been interpreted to indicate concentrated cross-shelf currents, which transport sediment away from shore during storms. However, recent observations strongly suggest that they are associated with sediment transport along-shore. A new hypothesis for the origin of these features begins with the observation that where a shallow seabed is covered by coarse material, that sediment is sculpted into large wave-generated ripples. Wave motions interacting with these large roughness elements will generate large-scale, energetic turbulence. This enhanced turbulence will tend to enhance the entrainment of fine sediment, and to inhibit its redeposition locally. Then, any mean current will tend to advect the fine sediment to a location where the bed is finer, the wave-generated ripples are smaller, and the turbulence is less energetic. Starting from a nearly homogeneous seabed, these interactions will tend to preferentially remove fine sediment where the bed is coarser, and to preferentially deposit it where the bed is finer, producing accumulations of fine material separated by self-perpetuating coarse domains. Research to test the hypothesis that this feedback and subsequent interactions between sorted features could produce large-scale sorted patterns with the characteristics observed in nature will consist of two linked parts: 1) field measurements of turbulence and suspended sediment concentrations, using tripod-mounted instruments located in both coarse and fine domains on a well-studied shoreface off Wrightsville Beach, North Carolina; and 2) development of a numerical model simulating these processes and the evolution of the seafloor. The field program will rigorously characterize interactions between coarse concentrations and sediment entrainment and deposition. Field data would subsequently be used to direct and constrain model development. This model will investigate what sediment-transport relationships that arise from the small-scale processes, and what environmental conditions, are sufficient to produce bedforms similar to the features observed.

根据这项裁决，PIS将调查涟漪状天灾洼地或分类床型的起源和意义。它们是在内陆架上相对较粗的沉积物中发现的，这些沉积物沿海岸方向延伸千米，宽约100米。此前，这些被解释为集中的跨陆架洋流，在风暴期间将沉积物从海岸上运走。然而，最近的观察强烈表明，它们与沿岸的泥沙输送有关。对于这些特征的起源，一个新的假说始于这样的观察：在浅海海床被粗糙的物质覆盖的地方，沉积物被雕刻成巨大的波浪产生的涟漪。与这些大粗糙度元素相互作用的波动将产生大范围、高能量的湍流。这种增强的湍流将倾向于增强细颗粒泥沙的夹带，并抑制其局部再沉积。然后，任何平均水流都将倾向于将细小的沉积物平移到一个位置，在那里河床更细，波浪产生的涟漪更小，湍流的能量更小。从近乎均匀的海床开始，这些相互作用将倾向于优先清除海床较粗的地方的细小沉积物，并优先将其沉积在海床较细的地方，产生由自我延续的粗域分隔的细小物质的堆积。为了检验这一假设，即这种反馈和分类特征之间的随后相互作用可以产生具有自然界中观察到的特征的大规模分类模式，这项研究将由两个相互关联的部分组成：1)使用安装在北卡罗来纳州莱特斯维尔海滩附近经过充分研究的海岸面上的三脚架安装的仪器，对湍流和悬浮泥沙浓度进行现场测量；2)开发一个模拟这些过程和海底演变的数值模型。现场计划将严格描述粗浓度与泥沙夹带和沉积之间的相互作用。随后，现场数据将用于指导和约束模型开发。该模型将研究小尺度过程中产生的泥沙-输运关系，以及什么环境条件足以产生与所观察到的特征相似的河床形态。