TIDAL CURRENT MOVEMENT AND ITS BEARING ON SEDIMENT TRANSPORTATION ON LIAODONG SHOAL
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摘要: 渤海东部的辽东浅滩是由一系列大致平行的线性沙脊和沙脊间沟槽共同组成的现代潮流地貌。根据辽东浅滩海域表层沉积物、脊-槽海流与悬浮泥沙同步观测和水深地形测量等资料,研究了沙脊和沟槽表层沉积物分布、海流及悬浮泥沙分布特征,分析了沉积物输运趋势,探讨了沙脊-沟槽地貌分布对潮流的响应。结果表明:辽东浅滩沙脊脊部表层沉积物为砂,沟槽表层沉积物为砂质粉砂和粉砂质砂,具有脊部粗、沟槽细的分布特征。受脊槽地形的控制,沙脊区潮流流速由表层至底层逐渐减小,沙脊脊部表层流速小于沟槽表层流速,而近底层则相反,沙脊脊部底层流速大于沟槽底层流速,其变化的临界深度约0.7 H(H为水深值)。沙脊区沉积物运移方向为NNE向,在一个潮周期内,沙脊脊部表层沉积物约有8.5~10.5 h可以被起动,而沟槽内沉积物只在高低潮流速较大的1h期间可以被起动。在长期的往复潮流作用下,沙脊脊部遭受侵蚀,沟槽淤积,沙脊逐渐退化,脊-槽高差减少,脊-槽地形趋于夷平,但沙脊退化的过程是缓慢的,目前的脊-槽地貌格局仍具有一定的稳定性。Abstract: Parallel linear sand ridges and troughs are widely distributed on the Liaodong Shoal in the eastern Bohai Sea.Based on the distribution data of surface sediments,the simultaneous observation of sand ridges, current movement and suspended sediment transportation as well as the bathymetric survey on the Liaodong Shoal,the distribution pattern of surface sediments on sand ridges and in troughs are studied together with the movement of the tidal currents and suspended sediments.The transport trend of sediments, the response of sand ridges and troughs distribution to tidal current are discussed.The results show that coarse sands occur mainly on sand ridges,while sandy silt and silty sand dominate troughs. Controlled by submarine topography,the current speed upon sand ridges is lower than that in troughs on the surface layer,but opposite near the bottom,and the critical depth is about 0.7 H (H is water depth). The sediments migrate on sand ridges along the direction of NNE.In a tidal cycle,the surface sediments on sand ridges may be kept in moving for 8.5~10.5 hours,while in troughs the sediments can only move for 1hour during the flood and ebb tide when the currents speed is high.Under the long-term cyclic actions of tidal current,sand ridges will be gradually eroded,while sedimentation happens in troughs,resulting in degeneration of sand ridges,and the height difference between sand ridges and troughs decreases so that the seabed terrain become flat eventually.However,this process takes time and the current geomorphic pattern of the Liaodong Shoal will remain stable for a long period.
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Key words:
- sand ridges /
- sediment movement /
- sediment transport /
- Liaodong Shoal
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