南黄海辐射沙洲地区奇异潮汐的时空分布特征和动力学机制研究

Co-oscillating tide, also called "odd-tide" is a kind of abnormal phenomenon of high tide. It usually comes without any sign and the associated flood roars on, swift and violent. The South Yellow Sea Radial Sand Ridges are featured by broad beaches and large tidal amplitude. The "odd-tide" happens frequently here. Previous studies tended to focus only on case-study analysis while lacking the summary on the local characteristics of space and time, as well as the exploration of the factors and generation mechanism for the "odd-tide". This study will focus on the "odd-tide" in the South Yellow Sea Radial Sand Ridges. It will start from collecting historical documents, hydrological records, and measured data, to standardize the definition of "odd-tide" in this area; parameterized its waveform and kinematics characteristics. A three-dimensional hydrodynamic model will be employed to cover the hydrodynamics over the South Yellow Sea Radial Sand Ridges. It will be used to quantify the integrity tendency and regional features of "odd-tide". By establishing the idealized models, the tests will be operated to find out the sensitivity of the "odd-tide" to a variety of external elements； multidimensional regression models will be built to interpret the correlations between the external motivation factors and the characteristic parameters of "odd-tide". Starting from the momentum balance equation, by means of combining theoretical analysis and numerical simulation, this study will analyze how the associated momentum terms, such as advection, secondary bottom friction, Coriolis force, influence the water level gradient; in order to reveal the dynamic mechanism of the formation, development and decline of the "odd-tide".

奇异潮汐，又称“怪潮”，是一种异常高潮位现象，它的出现没有征兆且来去迅猛，对沿海居民的人身和财产安全威胁极大。南黄海辐射沙洲，滩涂宽广，潮汐振幅大，是奇异潮汐的多发地区。但前人的研究往往注重个案分析，对当地奇异潮汐的时空分布特征、诱发因素和产生机制还缺乏总结和探索。因此本课题拟以发生在该海域的奇异潮汐为研究对象，从历史文献、水文记录、实测资料出发，拟标准化该地区奇异潮汐的定义，参数化其波形和运动学特征，通过构建覆盖南黄海辐射沙洲的三维水动力模型，量化奇异潮汐在南黄海的整体性态势和区域性特征；拟通过建立多维回归模型，诠释外部动力因素与其特征参数的相关性，并通过建立理想化数值模拟实验，测试其对外部各要素的敏感度；从动量平衡方程出发，通过理论分析和数值模拟相结合的手段，研究对流项、二次底部摩阻、科氏力等各项对水位梯度的影响，拟以此揭示该海域奇异潮汐产生、发展和衰败的动力学机制。

本项目针对南黄海辐射沙洲地区奇异潮汐，对该海域潮波运动进行了系统研究。通过收集实测资料和历史文献对潮形畸化进行定量分析，定义了奇异潮汐的相关参数；通过参数化奇异潮汐事件，分析了其具体表征；同时对可能触发奇异潮汐的因素进行排查。研究发现南黄海辐射沙洲地形要素对奇异潮汐的影响显著，同时研究发现近岸潮波运动规律、潮形畸化和动力学特征对岸线变迁的反响强烈，得到的主要结论有：奇异潮汐是一种普遍存在的近岸高频水位扰动现象，而并非南黄海辐射沙洲所独有。之所以在南黄海所闻名，与该地区潮滩宽广、滩涂作业量多、所造成的人生安全事故多有关。通过对气象因子的排除，初步判定该现象的生成机制与地形要素相关。南黄海辐射沙洲的辐射沙洲地形是影响这里潮波形态、潮流流速、潮能通量、潮能耗散的关键因素。潮波进入辐射沙洲系统后波形发生了严重的形变，落潮历时大于涨潮历时，且这种差异在潮流水道的顶端和沙脊的顶端最明显，涨落潮潮差也随之增大；该非线性现象由潮波进入辐射沙洲后在前进过程中与地形相互作用而产生，且越接近近岸，水深越浅，这种差异也越大。南黄海辐射沙洲近30年来岸线变化显著。本研究通过遥感数据及水动力模型，系统性地研究了该海域潮波特性对岸线变化的响应。研究发现岸线变化对潮波运动规律的影响显著。其中，M2/M4与M2/S2/MS4、K1/O1/M2的相互作用是该海域潮形畸化最主要的三个因子。在北部海域，潮形畸化的产生主要源于天文潮汐组合的非线性交互作用，并受制于M2潮能通量的直接变化。而在南部海域，M4和MS4浅水分潮主导了这里的潮形畸化，而浅水分潮的相位、振幅对滩涂或潮滩的规模和位置、刚性岸线的布局等在辐射沙洲地区非常敏感，以致于局地的岸线变迁会带来浅水分潮在此海域大格局的变化，从而改变了此地潮形基本特征。本研究可为后续的围垦规划提供科学依据，具有重要的学术价值和工程应用价值。