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Investigating Physical Processes Associated with Chesapeake Bay and Changjiang Estuary

机译：切萨皮克湾和长江口相关的物理过程研究

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摘要

Coastal and estuaries are landforms that not only have great impacts on large marine ecosystem, but also play a significant role in moderating or aggravating natural hazards and erosion risks that are expected to increase with climate change. This dissertation explores some of the concerns associated with coasts and coastal systems. In the second chapter, a thirty seven year wave hindcast (1979--2015) in Chesapeake Bay using NCEP's Climate Forecast System Reanalysis (CFSR) wind is presented. The long-term significant wave heights are generated by the third-generation nearshore wave model SWAN, which is validated using the wave height measurements at buoy stations inside the bay. Validation results show a good agreement between simulations and measurements. Statistical analyses on the simulated wave heights are carried out. Firstly, an Empirical Orthogonal Function (EOF) analysis is performed to study the temporal and spatial variability of significant wave heights in the bay. Secondly, the long-term changing trends of extreme wave heights are examined using regression analysis and empirical cumulative distribution function approach, which reveal a steady increase of extreme wave heights in most parts of the Chesapeake Bay in the past several decades. Finally, extreme value analyses based on generalized extreme value and generalized Pareto distribution functions are applied to evaluate design wave heights with different return periods. The effects of key parameters including threshold value, time span and data length on the design wave heights are extensively studied. Through the comparisons of different distribution functions evaluated by Bayesian Information Criterion and Akaike Information Criterion, it is found that Gamma distribution function and generalized extreme value analysis provide the best fit for annual and monthly data, while generalized Pareto distribution function gives the best fit when peak-over-threshold analysis is conducted. In the third chapter, sediment deposition in the north passage of the Changjiang Estuary, where the Deep-water Navigation Channel (DNC) is located, has been studied. To understand the suspended sediment dynamics and the effects of sediment-induced stratification on sediment flux in the navigational channel, field data on tidal ow and suspended sediment concentration (SSC) are collected and analyzed in this study. It is shown that net sediment transport is dominated by ebb currents in the study area. The net sediment flux is generally toward the ocean and the maximum value is found to be in the middle reach of the passage. In the lower reach of the passage, the net sediment flux is landward in the lower layer and seaward in the upper layer of the water column due to the two-layer feature of the estuarine circulation. Advective flux plays a significant role in transport of sediment in upper and middle reach of the passage by carrying 70~100% of the suspended sediment. However, this amount is reduced to 30~60% in lower reach of the passage where tidal effects become more important. The suspended sediment induced stratification in the north passage is examined by calculating eddy viscosity. It is found that suspended sediment can reduce eddy viscosity by 10~30%. The highest depth-averaged SSC is located in the middle reach of the north passage, where the averaged SSC is 4~15 times higher than that in the upper reach. In this region, bed shear stress is larger at ebb while SSC is higher at food. It is inferred that suspended sediments in the DNC during food are partially transported from a neighboring shoal, which plays an important role in sediment dynamics in the north passage.
机译：沿海和河口是不仅对大型海洋生态系统有重大影响的地貌，而且在缓和或加重预计随着气候变化而增加的自然灾害和侵蚀风险方面也起着重要作用。本文探讨了与海岸和沿海系统有关的一些问题。在第二章中，介绍了使用NCEP的气候预报系统再分析（CFSR）风在切萨皮克湾进行的37年海浪后预报（1979--2015）。长期的重要波浪高度是由第三代近岸波浪模型SWAN生成的，该模型使用海湾内部浮标站的波浪高度测量结果进行了验证。验证结果表明仿真和测量之间有很好的一致性。对模拟波高进行统计分析。首先，进行了经验正交函数（EOF）分析，以研究海湾中重要波高的时空变化。其次，使用回归分析和经验累积分布函数方法研究了极端海浪高度的长期变化趋势，这揭示了切萨皮克湾大部分地区过去几十年来极端海浪高度的稳定增长。最后，基于广义极值和广义帕累托分布函数的极值分析被应用于评估具有不同返回周期的设计波高。广泛研究了关键参数（包括阈值，时间跨度和数据长度）对设计波高的影响。通过贝叶斯信息准则和Akaike信息准则评估的不同分布函数的比较，发现伽玛分布函数和广义极值分析最适合年度和月度数据，而广义帕累托分布函数最适合峰值时的拟合。 -阈值分析。第三章研究了深水航道（DNC）所处的长江口北通道的沉积物。为了了解悬浮泥沙动力学和泥沙诱导分层对航道中泥沙通量的影响，本研究收集并分析了潮汐流和悬浮泥沙浓度（SSC）的现场数据。结果表明，研究区的净沙流主要由退潮控制。净沉积物通量通常朝向海洋，并且最大值位于通道的中部。在河道的下游，由于河口环流的两层特征，净沉积物通量在水柱的下层向内，在水层的上层向海。正向通量通过携带70〜100％的悬浮泥沙而在通道的中上游输送泥沙中起着重要作用。但是，在潮汐影响变得更加重要的较低通道范围内，该数量减少到30％至60％。通过计算涡流粘度来检查北通道中悬浮沉积物诱发的分层。发现悬浮的泥沙可以使涡流粘度降低10〜30％。最高平均深度的SSC位于北通道的中段，平均深度比上游的高4〜15倍。在该区域，床的剪切应力在退潮时较大，而在食物中的SSC较高。可以推断，食物中DNC中的悬浮沉积物是从邻近的浅滩中部分运走的，这在北通道的沉积物动力学中起着重要作用。

著录项

  • 作者

    Niroomandi, Arash.;

  • 作者单位

    Old Dominion University.;

  • 授予单位 Old Dominion University.;
  • 学科 Civil engineering.;Climate change.;Physical oceanography.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 103 p.
  • 总页数 103
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 古生物学;
  • 关键词

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