Tidal flat erosion of the Huanghe River Delta due to local changes in hydrodynamic conditions
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摘要: 1964~1976年期间黄河经刁口流路注入渤海形成的三角洲叶瓣潮滩提供了一个理想的研究波浪荷载作用下后期堆积沉积物动态变化过程的天然实验室。1995年为开采石油在潮间带上修建的一条路堤显著改变了两旁潮间带区域的海洋水动力条件。相同的初始沉积环境、活跃的波浪荷载作用、后期不同的水动力条件、足够长的作用时间、水深很浅的潮间带环境为现场试验研究的开展提供了便利条件。在路堤的两侧分别选择一个研究区进行现场测量、取样、室内实验和数据分析计算,包括地貌资料、水动力条件、沉积物性质、粒度成分和地貌数据分维计算。观测结果表明,大风浪荷载作用居多的路堤外侧,潮滩凹凸不平、高侵蚀速率、高分形维数,而且随着计算矩阵的增大地貌分维值降低速度很快;在水动力条件较弱的路堤内侧,潮滩平坦、侵蚀速率低、地貌分维值低,随着计算矩阵的增大地貌分维值变化微小,并且当计算矩阵值趋向临界值时,不同水动力区域的地貌分维值均衡增长。两个相邻研究区潮滩地貌与沉积物侵蚀速率的显著差异,揭示了海洋水动力条件对海底地貌改造与水下三角洲侵蚀过程的重要作用。水动力差异导致的沉积物性质、粒度成分、微结构特征与矿物成分的后期分异过程对两个相邻研究区海底地貌与侵蚀过程的后期分化做出了重要贡献。Abstract: An ideal nature system for the study of post-depositional submarine mass changing under wave loading was selected in the inter-tidal platform of the subaqueous Huanghe River Delta, a delta formed during period from 1964 to 1976 as the Huanghe River discharged into the Bohai Gulf by Diaokou distributary. A road embankment constructed for petroleum recovery on the inter-tidal platform in 1995 induced the essential varieties of hydrodynamic conditions on the both sides of the road. With both sides sharing similarities in (1) initial sedimentary environment, (2) energetic wave loading, (3) differential hydrodynamic conditions in later stages, (4) enough long-range action, and (5) extreme shallow water inter-tidal platforms;the study is representative and feasible as well. Two study sites were selected on each side of the road, and a series of measurements, samplings, laboratory experiments have been carried out, including morphometry, hydrodynamic conditions, sediment properties, granularity composition, and fractal dimension calculation of the topography in the two adjacent areas. It was observed that in the outer zone, where wave loading with high magnitude prevailed, the tidal flat was bumpy and exhibited a high erosion rate and high fractal dimension. Further, the fractal dimension diminished quickly, keeping with the enlarging of calculative square size. However in the inner zone, where the hydrodynamic condition was weak, the tidal flat was flat and exhibited a low erosion rate and low fractal dimensions;the fractal dimension diminished with the enlarging of calculative square size. The fractal dimensions in the different hydrodynamic areas equalized increasingly as the calculative square size accreted to threshold, indicating that the hydrodynamic condition plays a significant role in topography construction and submarine delta erosion process. Additionally, the later differentiation of sediment properties, granularity composition, microstructure characteristics, and mineral composition induced by the different hydrodynamic conditions can also contribute to the variation of topography and sea-bed erosion in the two adjacent areas.
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Key words:
- hydrodynamic conditions
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