围填海工程对半封闭海湾水动力环境的影响

Hydrodynamical influence of reclamation projects in a semi-closed bay

为研究围填海工程对海湾水动力环境的影响,本文基于二维数值模型MIKE21,建立了东山湾附近海域的潮流模型。对比观测数据发现,大潮期间的最高、最低潮位模拟误差在6 cm以内,小潮期间的误差相对较大;流速和流向的模拟误差在9%左右,最大误差出现在转流时刻;总体来看,模拟结果与观测数据吻合良好。在此模型基础上,研究了东山湾围填海前、后潮流动力、水体半交换时间和纳潮量等水动力要素的变化。结果表明:围填海后大范围的涨落流态与围填海前保持一致,大体上仍然呈现S-N走向,涨潮流偏N向,落潮流偏S向,往复流特征较为明显;从局部流场来看,涨落潮流场发生了一定的变化,围填海区域南、北两侧的流矢变化较为明显,涨潮流矢由偏N向改为偏E向,而落潮流矢由偏S向改为偏W向,同时受到围填海区域岸线的遮蔽效应,围填海南、北两侧水域的流速也有一定减弱,而西侧的流速则有一定增强;围填海实施前的水体半交换时间为220.5 h,实施后时间为239.4 h;纳潮量变化为–2.5%左右。研究表明,围填海工程对东山湾水动力环境的影响主要集中在工程区域附近,其对泥沙冲淤、生态环境等的影响将在后续研究中进一步探讨。

Based on a two-dimensional numerical model-MIKE21,tides and tidal currents in the semi-enclosed Dongshan Bay was simulated to study on the hydrodynamical influence of reclamation projects in the bay.By comparison to observations,errors in simulated highest and lowest tidal levels are within 6 cm during spring tide,while those during neap tide are relatively larger.Errors in simulated flow velocity and flow direction are around 9%,with the maximum mainly occurs at the turning moment of tidal current.Overall,model results are well agreed with the field observations.Therefore,the tidal hydrodynamics,the water’s semi-exchange time and the tidal prism in the Dongshan Bay before and after the reclamation projects were numerically compared based on the well veri-fied model.Results show that the general type of tidal current after the reclamation stays in consistent with that before the projects.Tidal current still flows along south-north direction,with flood flows northward and ebb flows southward.The reciprocating characteristic is obvious.From the local flow field,there has been a certain change in the ebb and flow field,especially the tidal currents on the south and north sides of the reclamation area.The flood flows change from the northward to the eastward,while the ebb flows change from the southward to the westward.At the same time,due to the shadowing effect of the shoreline in the reclamation area,the flow velocity around the south and north sides of the reclamation is also weakened,while the flow velocity on the west side is enhanced to some extent.The water’s semi-exchange time before the reclamation is 220.5h,and the time afterwards is 239.4h.The change of the tidal prism is about–2.5%.The study found that the impact of the reclamation project on the hy-drodynamic environment of Dongshan Bay is mainly concentrated in the vicinity of the project area,and its impact on sediment erosion and deposition,ecological environment,etc.will be further explored in subsequent research.