| 摘要: |
| 基于2018年8月福建三沙湾湾内外共两个定点站位的船基和座底三脚架观测数据，研究了三沙湾底边界动力过程及悬沙输运特征。结果表明，三沙湾湾内湾外两个站位均表现出涨落潮历时相近但涨落潮流速明显不对称的现象，即湾内涨潮流速大于落潮流速，湾外则相反。湾内水体受淡水输入影响较大，表现出落潮期间显著的温盐层化，而涨潮期间水体混合良好；湾外水体受淡水影响不明显，表现为水体温度主导的层化。通过对底边界层动力过程的分析表明，湾内（距底0.75 m）、湾外（距底0.50 m）站位底边界层的平均摩阻流速分别是0.016 m/s、0.013 m/s，且两个站位拖曳系数基本相等（2.03×10-3），表明在相同流速下湾内站位的底部切应力更大，近底沉积物再悬浮和搬运相对湾外站位更为显著。因此观测期间悬沙浓度最大值出现在湾内站位，为109 mg/L，且悬沙在垂向上的分布可达上层水体；湾外站位悬沙浓度更低，并且底部悬浮泥沙仅能影响至距底5 m的水体。悬沙通量机制分解结果表明，三沙湾夏季的潮周期单宽悬沙从湾外向湾内方向净输运，湾内站位向湾内方向净输运74.88 g/（m·s），平流输沙占主导作用，贡献率41.7%；湾外站位向湾内方向净输运10.57 g/（m·s），主要受平流输沙和垂向净环流的控制，贡献率94.9%。 |
| 关键词: 三沙湾 底边界层 摩阻流速 悬沙输运 悬沙机制分解 |
| DOI：10.11759/hykx20210227002 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41976070）；中国地质调查局项目（DD20189505） |
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| Hydrodynamic processes of the bottom boundary layer and suspended sediment transport in the Sansha Bay in summer |
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QI Yu-kai1, TU Jun-biao1, YU Jun-jie2, FAN Dai-du1
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1.State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2.Nanjing Geological Survey Center, China Geological Survey, Nanjing 210016, China
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| Abstract: |
| In this study, a detailed field observation is conducted on the hydrodynamic processes of the bottom boundary layer and suspended sediment transport mechanisms at two sites inside and outside the Sansha Bay in August 2018. Results show that the two sites in the inner bay and the outer bay show similar ebb and flood durations but exhibit asymmetry in the ebb and flood velocity. The flow velocity of the inlet is greater than that of the ebb tide, but the opposite is true outside the bay. The water column in the bay is greatly affected by fresh water, showing significant temperature and salinity stratification during the ebb tide, while the water mixes well during the flood tide. The water outside the bay is thermally stratified and not considerably affected by the fresh water. The analysis of the hydrodynamic processes of the bottom boundary layer shows that the average friction velocity of the bottom boundary layer at the site in the bay (from the bottom of 0.75 m) and outside the bay (from the bottom of 0.50 m) are 0.016 and 0.013 m/s, respectively. The drag coefficients of the two sites are basically the same (2.03×10-3) at different heights. This indicates that the bottom shear stress inside the bay is greater than that outside the bay at the same current velocity. Thus, the resuspension and transport of near-bottom sediments inside the bay are more significant than those outside the bay. Therefore, during the observation period, the maximum suspended sediment concentration appeared at the site inside the bay (109 mg/L) and the vertical distribution of the suspended sediment could reach the upper layer. Moreover, the suspended sediment concentration outside the bay was lower, and the suspended sediment was confined in the lower from the bottom of 5 m. Results of the mechanism decomposition sediment transport indicate that during summer, the net suspended sediment transport was from the outer bay to the inner bay. At the inner bay, the dominant mechanism of the suspended sediment transport is advection, which contributes 41.7% of the total sediment flux. As a result, the net suspended sediment transport is 74.88 g/(m·s). At the outer bay, the net suspended sediment transport is 10.57 g/(m·s) from the outer bay to the inner bay, mainly controlled by advection and vertical net circulation with a contribution rate of 94.9%. |
| Key words: Sansha Bay bottom boundary friction velocity sediment transport decomposition of suspended sediment mechanism |
