围填海对伶仃洋水流动力的短期影响模拟研究

利用已经过验证的高分辨率三维海洋动力模型FVCOM,根据1984—2014年内伶仃洋的围填海变化情况,结合情景模拟案例,研究分析围填海对伶仃洋水流动力的影响,探究截流式和顺流式围填海对伶仃洋不同季节的水平余流场、垂向环流结构以及潮汐变化过程的影响。研究结果表明,围填海对伶仃洋的余流流向没有明显影响,但对余流速有较大的影响。在水平方向上,截流式围填海使得周边海域的余流速明显增大,增幅在0.02~0.25 m/s不等,其中口门区域受到的影响最大;相较于底层流场,表层流场受围填海的影响相对更大,围填海以南的较远海域在表层出现一条强度逐渐减弱的流速减小带,减幅在0.02~0.15 m/s不等,且影响范围与流场的分布密切相关,在夏季向南延伸,在冬季向西南延伸。顺流式围填海的影响则主要分布在伶仃洋两侧沿岸,并且不同季节的影响特点有一定区别,在夏季使得内伶仃洋东岸海域流速增大,但在冬季使其流速减小,变化幅度均在0.02 m/s以上。在垂直方向上,围填海使口门区域余流的纵向流速梯度增加,并且改变了伶仃洋余流的垂向分布情况,总体表现为远离围填海的海域表、底层余流的流速减小,中上层余流的流速增大;与此同时,围填海大幅度改变了周边海域的横向流速,并且在伶仃水道、矾石水道等区域产生了新的横向环流。围填海使得河口至围填海的余水位明显上升,使得伶仃洋海域的余水位下降,余水位梯度的增大是围填海周边余流速增大的主要原因。另外,围填海影响了伶仃洋的潮汐变化过程。在大潮期间,围填海改变了伶仃洋海域涨落潮时的潮流流速,使得周边海域落急流速增加,较远海域落急流速减小,而涨急流速都减小;同时,围填海使得海域涨落潮时的潮位受到一定影响。围填海最终使得伶仃洋的潮汐相位提前了20~35 min。

A model study on the short-term impact of reclamation on the hydrodynamic processes in the Lingdingyang Bay

According to the changes of the reclamation in the Lingdingyang Bay during 1984-2014, the impact of reclamation on the hydrodynamic in the Lingdingyang Bay was investigated using a validated high-resolution FVCOM model. The effects of two different types of reclamation on the horizontal residual currents, vertical circulation structure and tidal process in different seasons in the bay were explored. The results show that the reclamation has no significant effect on the direction of the residual currents in the bay but has a notable impact on the velocities. In the horizontal direction, the blocking-currents reclamation increases the residual velocities significantly, ranging from 0.02 m/s to 0.25 m/s in the surrounding sea area, and the river outlets are most affected. Compared with the bottom currents, the surface currents are more affected by the reclamation. In the sea area far away from the reclamation, a decreasing velocity zone with a gradually weakening intensity appears at the surface, ranging from 0.02 m/s to 0.15m/s. The range of influence is closely related to the distribution of the flow field, extending southward in summer and southwest in winter. The effects of downstreams reclamation are mainly distributed on both sides of the Lingdingyang Bay, and there are different characteristics in different seasons. The residual flow velocities in the eastern shore of the bay are increased in summer but reduced in winter. Both the variation range are above 0.02 m/s. In the vertical direction, the reclamation of the sea increases the longitudinal velocities gradient of the residual flow in the entrance area and changes the vertical distribution of the residual flow in the bay. In general, the residual flow velocities of the surface and bottom layer are reduced and the velocities of the upper middle layer are increased in the sea areas far away from the reclamation. At the same time, the reclamation greatly changes the lateral velocities of the surrounding waters, and new lateral circulations are generated in some area such as the Lingding and Fanshi waterways. The reclamation causes the residual water level to increase significantly from the river outlets to the reclamation areas and causes the water level to reduce in the sea areas. The increase of the residual water level gradient is the main reason for the increase of the residual flow velocities around the reclamation areas. In addition, the reclamation changes the tidal process. During the spring tide period, the reclamation changes the flow velocities during the flood and ebb tide, which increases the peak velocities during ebb tide surrounding sea but reduces it on the farther sea. The peak velocities during flood tide are reduced in the whole sea area. Meanwhile, the reclamation has affected the water level during the flood and ebb tide. Eventually, the reclamation makes the tidal phase of Lingdingyang arrive at 20 to 35 minutes in advance.