| 摘要: |
| 海底沉积物运动可由重力作用引起，它常以水下滑坡的形式出现，对高含水量的细颗粒物质尤其是如此(林振宏等，1990)；在陆架和陆坡区，水下滑坡可由于地震等事件而诱发。此外，海底稳定性还与水流作用引起的沉积物运动有关，沉积物输运造成相应的堆积和冲刷，从而改变海底的形态。在许多环境中，沉积物输运是控制海底稳定性的主要因素。海底某处高程在一定时段内的变化系由活动层厚度、冲淤量和底部地貌形态(Bedforms)迁移造成的变化等3部分构成(图1)，故海底稳定性可分解为以下3个问题：(1)沉积物活动时间(即在一定时段内海底沉积物处于运动状态的时间长度或百分比)和活动层厚度(图1A)；(2)沉积物运动所造成的冲刷、淤积及其速率(图1B)；(3)底部地貌形态的迁移速率及其造成的海床高程变化(图1C)。
海底沙丘和潮流沙脊是常见的海底地貌形态，有关专家认为(Ashley et al., 1990)，海底沙丘是大沙波(波长>30m)、小沙波(波长6-30m)、大波痕(波长0.6-6m)等形态的总称，它可以在沉积物供给充足、大潮流速达到0.6-1.0m/s的海底形成(Stride，1982)。潮流沙脊的规模大于海底沙丘，其高度可达20m以上，两脊之间相距10km左右，形成的流速条件为0.7-1.3m/s，其脊线几乎平行于潮流流向。海底沙丘和湖流沙脊的空间分布上往往具有重现性，即可以形成一系列的沙丘或沙脊。据沉积动力学研究的初步结果，这种周期性的分布与潮流流场特征(如潮流长短轴之比，主流流速、主流不稳定性等)和海底沉积物平面分布的非均匀性有关(Huthnance，1982a, 1982b；Hulscher et al.，1993；Liu，1997)。潮流沙脊可与海底沙丘伴生(Stride，1982；Amos et al.，1984)，此类形态的存在说明海底是处于活动和演变的状态，这往往给海洋工程带来一系列的问题。
本文应用水动力学、沉积动力学数学模型方法对砂质海底的上述3个问题分别提出解决方案，从而建立海底稳定性的评估方法。本文还叙述了来自海南岛西部海域的一个算例，以说明该方法的应用步骤和结果解译。 |
| 关键词: 沉积物输运 砂质海底 沙脊 |
| DOI： |
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| 基金项目:中国科学院海洋研究所调查研究报告第4098号。国家杰出青年科学基金资助项目，49725612号。 |
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| METHODOLOGY FOR EVALUATING THE STABILITY OF SANDY SEABED CONTROLLED BY SEDIMENT MOVEMENT, WITH AN EXAMPLE OF APPLICATION |
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Gao Shu, Fang Guohong, Yu Kejun, Jia Jianjun
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Institute of Oceanology, Chinese Academy of Sciences
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| Abstract: |
| Sediment movement patterns control the stability of sandy seabed in three aspects: (ⅰ)the sediment edibility time and the thickness of the moving layer; (ⅱ)seabed accretion/erosion and their rate; and (ⅲ)seabed elevation changes in response to bedform (e.g. underwater dunes and tidal ridges) migration. These problems can be solved by the following procedures. Firstly, the sediment erodibility time and the rate of bed-load transport are calculated using an appropriate equation which takes into account the combined effect of waves and tidal currents. Secondly, the moving layer thickness and the accretion/erosion rate are estimated using the transport rate data. Finally, the information on the migration velocity of dunes/ridges and the resultant seabed elevation changes is obtained using the transport data and the geomorphic data of the bedform. As an example for its usage, we applied the method to the assessment of seabed stability over an area to the west of Hainan Island. The results show that the seabed material is highly mobile, with active sediment movement. The rate and amplitude of seabed elevation changes are both relatively large, in response to rapid bedform migration. These characteristics must be taken into account in the development of the natural resources of the region. |
| Key words: sediment movement stability sandy seabed |
