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

根据该奖项，pi将调查波纹状洼地或分类床的起源和意义。它们位于内陆大陆架上相对粗糙的沉积物中，沿海岸方向延伸数公里，宽度约为100米。以前，这些现象被解释为表明在风暴期间将沉积物从海岸带走的集中的跨大陆架洋流。然而，最近的观测强烈表明，它们与沿岸的沉积物运输有关。一种关于这些特征起源的新假设开始于对浅海底被粗糙物质覆盖的地方的观察，这些沉积物被雕刻成波浪产生的大涟漪。波浪运动与这些大的粗糙元素相互作用将产生大规模的高能湍流。这种增强的湍流倾向于增强细粒沉积物的夹带，并抑制其局部再沉积。然后，任何平均水流都倾向于将细沉积物平流到一个河床更细、波浪产生的涟漪更小、湍流能量更低的地方。从几乎均匀的海床开始，这些相互作用将倾向于优先移走河床较粗的细沉积物，并优先将其沉积在河床较细的地方，产生由自我延续的粗域隔开的细物质堆积。为了验证这种反馈和分类特征之间的后续相互作用可以产生具有在自然界中观察到的特征的大规模分类模式的假设，研究将包括两个相关的部分：1)湍流和悬浮沉积物浓度的现场测量，使用安装在三脚架上的仪器，分别位于北卡罗来纳州赖特斯维尔海滩的一个经过充分研究的海岸表面的粗区和细区；2)建立模拟这些过程和海底演化的数值模型。现场计划将严格描述粗浓度与沉积物夹带和沉积之间的相互作用。现场数据随后将用于指导和约束模型开发。该模型将研究小规模过程中产生的泥沙运输关系，以及什么样的环境条件足以产生与观测到的特征相似的河床。

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.