Modeling Shoreline Morphological Evolution

许多沿海地区正在经历巨大的形态变化，导致栖息地和生计的恶化，并改变了陆地和海洋之间的交换。例如，在马萨诸塞州玛莎葡萄园岛的卡塔玛湾附近，沉积物的运输和形态演变正在影响水质、牡蛎养殖场、旅游业以及住宅和建筑。飓风艾琳和桑迪带来的海浪加上强劲的水流在卡塔玛湾附近造成了2.5米的侵蚀和堆积。此外，入口每年迁移数百米，最终会关闭，直到风暴再次打破将海湾与海洋分开的屏障海滩。该项目将结合现有的实地观测和数值模型模拟来确定这种形态演变的原因。通过调查潮汐、波浪和水流对玛莎葡萄园岛动态海岸的影响，该研究项目将使人们更好地了解在海洋海滩和入口或附近推动海岸线演变的过程。该团队将与美国地质调查局的科学家合作开发模型，以解决一系列未来的情景，并将与当地的利益相关者和管理者合作，提供模拟和信息，以应对不同的强迫和管理选择，以及帮助规划进水口关闭和相关的水质变化。该项目还将为高中生制作有关STEM主题的视频课程。该研究将解决以下假设：(1)入口的迁移是由于大型东北风和飓风的组合，更频繁，但更温和的波浪事件，以及强烈的潮汐流；(2)相对于洪水和退潮的风暴时间和风暴持续时间对形态演化很重要；(3)海湾内的增生是由沿岸携带的沙子引起的，随后在洪水期间被运送到入口。（iv）当一场大风暴与一次或多次大潮同时发生时，进水口会关闭，将沙子带入进水口。大的形态信号与现有的波浪、洋流观测和不断变化的水深测量相结合，使该站点成为解决海岸线形态演变假设的理想场所，可以校准、测试和改进模拟观测到的演变的数值模型，并使用模型预测不同情景下的未来变化。虽然这项研究将集中在玛莎葡萄园岛，那里有大量的观测数据和模型基础设施，但结果将适用于广泛的海岸线系统，无论是否有进水口。主导过程可能因地而异，但纳入模型的基本物理原理是相似的。

Many coastal areas are undergoing tremendous morphological change, resulting in deterioration of habitats and livelihoods, and altering the exchanges between land and ocean. For example, near Katama Bay, Martha's Vineyard, Massachussetts, sediment transport and morphological evolution is affecting water quality, oyster farms, tourism, and homes and structures. Waves from Hurricanes Irene and Sandy combined with strong currents caused 2.5 meter of erosion and accretion near Katama Inlet. In addition, the inlet is migrating hundreds of meters per year, and eventually will close until a storm again breaches the barrier beach separating the bay from the ocean. This project will use a combination of existing field observations and numerical model simulations to determine the causes of such morphological evolution. By investigating the effects of tides, waves, and currents on the dynamic coast of Martha's Vineyard, this research project will lead to an improved understanding of the processes driving shoreline evolution on ocean beaches and in or near inlets. The team will collaborate with U.S. Geological Survey scientists on model development for addressing a range of future scenarios and will work with local stake holders and managers to provide simulations and information about possible changes to the shoreline in response to different forcing and management choices, as well as to help plan for inlet closings and the associated changes in water quality and access. The project will also produce video lessons for high school students on relevant STEM topics.The study will address the hypotheses that: (i) migration of the inlet is owing to a combination of large nor'easters and hurricanes, more frequent, but more moderate wave events, and strong tidal flows, (ii) the timing of storms relative to flood and ebb flows and the storm duration are important to the morphological evolution, (iii) accretion inside the bay is caused by sand carried alongshore and subsequently transported into the inlet during flood flows, and (iv) closure of the inlet occurs when a large storm coincides with one or more spring flood tides, carrying sand into the inlet. The large morphological signal combined with existing observations of waves, currents, and the changing bathymetry make this site an ideal location to address hypotheses for shoreline morphological evolution, to calibrate, test, and improve numerical models that simulate the observed evolution, and to use models to predict future changes for different scenarios. Although this study will focus on the Martha's Vineyard site where there is substantial observational data and model infrastructure, the results will be applicable to a wide range of shoreline systems, with or without inlets. The dominant processes may differ from site to site, but the fundamental physics incorporated in the model are similar.