潟湖的悬沙输运特征与机制分析:以海南岛新村、黎安港为例

根据2013年8月在海南岛新村和黎安港潟湖定点站位进行的水位、流速和悬沙浓度的全潮测量数据, 分析了双湖的流速结构和悬沙浓度的时空分布特征; 同时, 利用机制分解法研究湾内悬沙输运特征和机制, 并探讨了双湖沉积动力过程与地貌特征的关系。结果表明, 新村、黎安港海域受不规则全日潮控制, 潮流为往复流, 落潮流略强于涨潮流; 本区悬沙浓度较低, 且变化不大, 属于低悬沙浓度、弱潮流作用的沙坝潟湖海岸。通量分解结果显示, 欧拉余流和潮汐捕捉效应是此海域悬沙输运的主要贡献项;其中, 新村港的悬沙输运以欧拉余流输运为主, 黎安港以潮汐捕捉效应和重力环流作用占优, 两湖悬沙均有向外海输运的趋势。

THE CHARACTERISTICS AND MECHANISM OF SUSPENDED SEDIMENT TRANSPORT IN LAGOON: A CASE STUDY FROM XINCUN AND LI-AN HARBORS,HAINAN ISLAND

The Xincun Harbor(i.e.18°23'~ 18°28'N, 109°57'~ 110°02'E) and Li-An Harbor(i.e.18°24'~ 18°27'N, 110°01'~ 110°04'E) were located in the southeast of Hainan Island.They were typical barrier-lagoon systems.Xincun Harbor covered an area of 19.43km2, with an average depth of 5.7m.The bottom sediment was characterized by sand.Li-An Harbor was smaller with an area of 7.92km2.It was connected to the South China Sea with a width of 60m inlet.Both Xincun and Li-An Harbors were lack of obvious runoff.As a result, the major hydrodynamic factors here were waves, tides and tidal currents.Previous research focused on hydrodynamics and tidal inlet evolution; few researchers had studied the mechanism of suspended sediment transport in the study area.In this study, we had four observation stations, i.e. S1 (18.410°N,109.984°E), S2 (18.424°N,110.014°E), S3 (18.408°N,110.056°E), and S4 (18.430°N,110.050°E), in order to measure the water level and current velocities by using ADCP and Valeport, and to collect multi-layer water samples during a tidal cycle in August, 2013.Then we analyzed the suspended sediment concentration by the filtration method in our laboratory.On such a basis, we got the current velocity structures and suspended sediment distribution patterns.Then we used Dyer's method to analyze the mechanisms of suspended sediment transport.The results showed that the Xincun and Li-An lagoons were mainly under the control of irregular diurnal tide.The tidal flow here was rectilinear.The ebb current was stronger than the flood current.In general, both Xincun and Li-An harbors were observed with weak tidal currents at the inner lagoon, but strong currents at the entrance(e.g. an maximum tidal current of 0.75m/s at the Li-An entrance).Further, residual currents were no greater than 0.043m/s.Eulerian residual currents played a dominant role in the total of Lagrange residual currents.In general, the suspended sediment concentration, ranging from 0 to 17.2mg/L, showed a vertical stratification.The suspended sediment was transported towards the open sea due to the time-velocity asymmetric characteristics.The analysis of transport mechanisms suggested that the Eulerian residual currents and tidal trapping effects controlled the suspended sediment transport pattern in the two lagoons.In Xincun Harbor, the Eulerian residual currents were dominant, whilst in Li-An Harbor both the tidal trapping effect and the gravity circulation worked greater than the other mechanisms.These observations indicated that under normal hydrodynamic conditions the two lagoon systems are both characterized by weak sediment transport.