渤海湾高强度开发对潮波系统的累积影响机制

Cumulative impacts of high intensity reclamation in Bohai Bay on tidal wave system and its mechanism

渤海湾2003年以来在不到十年内因高强度开发岸线形态变化极大,然而目前对此背景下潮波系统累积变化过程及其响应机制认识不足.选取渤海湾2003年、2006年、2012年、远期规划、0 m围填以及-5 m围填等6个代表围填阶段,利用二维潮波数学模型,通过对比整体围填与逐一累加围填对潮波系统变化的影响以及对比围填岸段潮差大小与潮波系统变化的对应关系,揭示了潮波系统累积变化过程及变化的主导机制,为认识人类对潮波系统的影响提供了客观依据.研究显示,渤海湾不同围填阶段对M_2分潮影响远大于对K_1分潮影响,且对黄河口外M_2分潮无潮点影响明显;围填规模增加使得该M_2分潮无潮点先向东南移动再向东北移动,海湾西部潮差先变大再减小,潮波传播速度先加快至0 m围填后趋于稳定,-5 m围填阶段潮波系统虽变化明显但湾内潮汐性质不变.从北向南逆时针方向逐一增加围填直至远期规划围填全部实施,该无潮点将先向西南再向东南移动.受旋转潮波控制的半封闭海湾,围填所在岸段潮差越大,对潮波系统影响越明显.持续围填将使海湾沿岸低地有被淹没的危险,使得湾内流速减缓,水交换减弱,还会影响黄河口附近冲淤以及海岸防护和设计标准.

Contiguous mudflats exist along the coast zone of the Bohai Bay in the western part of the Bohai Sea of China. They are generally suitable for land reclamation, which can ease the contradiction between land resource shortage and the demand for development, because mudflats are important geomorphological systems which provide land resources. The shoreline at the Bohai Bay has experienced significant changes since 2003 due to high intensity reclamation. Environmental impacts of reclamation at different stages, especially on the tidal wave system, have attracted worldwide attention. However, there is still a lack of understanding on the cumulative response process of the tidal wave system and its response mechanism to high intensity development of mudflats. In this study, six periods were selected as representative reclamation stages in the Bohai Bay： 2003, 2006, 2012, future planning, and 0 m and -5 m reclamation stages. A two-dimensional tidal wave mathematical model was developed to analyze the cumulative changing process and dominant mechanism of the change of the tidal wave system by comparing effects of reclamation of the entire bay and cumulative effects of sequential reclamation projects, as well as studying the relations between the tidal wave change and tidal range on the shore segment where the reclamation project is located. Based on the analysis results, the influence of reclamation in the Bohai Bay on the M2 constituent tide was much greater than that on the K~ constituent tide, especially on the M2 constituent tide amphidromic point outside of the Yellow River mouth. The movement distance of the M2 constituent tide amphidromic point outside the Yellow River mouth for the aforementioned reclamation stages compared to its location in 2003 was about 1, 10, 22.5, 27.3, and 83.8 kin, respectively. In contrast, the maximum movement distance of the other M2 constituent tide amphidromic point outside Qinhuangdao and the unique Kt constituent tide amphidromic point in the Bohai Sea for the aforementioned reclamation stages compared to their conditions in 2003 were about 5.9 and 6.3 km, respectively. With the increase of the reclamation scale, the M2 constituent tide amphidromic point outside of the Yellow River mouth first moved southeastward, and then moved northeastward, and the tidal range of the western Bohai Bay first increased and then decreased, while the speed of tidal wave propagation first accelerated and then stabilized during the 0 m reclamation stage. During the -5 m reclamation stage, the tidal wave system experienced obvious changes, however, the tidal properties inside the bay remained the same. The average tidal current velocity of the bay decreased with the increase of the reclamation scale, and the tidal current velocity of 2003, 2012, future planning and -5 m reclamation stages were 0.33-0.37, 0.3-0.34, 0.29-0.31, and 0.16-0.17 m/s, respectively. When reclamation projects were performed one by one counterclockwise from Caofeidian （future planning） in the north to south until all the future planned reclamation projects were completed, the M2 constituent tide amphidromic point first moved southwestward, and then moved southeastward. In semi-closed bays influenced by rotational tidal wave, the impact intensity of reclamation projects to the tidal wave system depends mostly on the tidal range of the coast where the reclamation projects are located. The greater the tidal range, the more obvious the effects of the reclamation projects will be on the tidal wave system. Continuous reclamation will increase flooding risks and tendency of siltation in the bay, weaken the water exchange rate in the bay, affect scouring and silting, as well as impact the design and defense standards of coastal engineering projects near the Yellow River mouth.