摘要
旁侧声纳图像和多波束水下地形测量清晰地揭示了杭州湾北岸水下岸坡4种微地貌形态,分别为冲沟、凹坑、沙波、光滑海底。金山深槽内海底扰动、切割十分强烈,微地貌以冲沟、凹坑为主,局部成沙波片发育。深槽外缘的水下平地微地貌特征主要表现为光滑海底和冲沟交替出现,局部也有沙波分布。旁侧声纳图像和底质综合分析表明杭州湾北岸水下地貌面貌是水动力和泥沙来源共同作用的结果:一方面,冲沟、凹坑和沙波代表的水流方向与涨潮流方向一致,指示了强劲的潮流对海床的侵蚀和改造;另一方面,由于底流水动力较强、底质沉积物粒径较细,冲沟得以普遍发育,而沙波仅在局部的砂质海床中出现。水下岸坡微地貌分布显示了海床侵蚀与地貌格局和水深条件密切相关,表现为主槽内冲刷和改造后再沉积作用较强,主槽外缘的水下平地冲刷作用明显变弱,出现弱能条件下的光滑海底;水下平地中,浅水区冲沟较为发育,深水区则以光滑海底为主。总体而言,杭州湾北岸水下岸坡侵蚀性微地貌广泛分布,海床处于侵蚀状态。
There are mainly four types of subaqueous microrelief（gully,hollow,ripple and smooth seafloor） on northern Hangzhou bay subaqueous slope,visibly revealed by side scan sonar records and underwater acoustic multi-beam bathymetric data.Inside the Jinshan trough,textured seafloor eroded strongly mainly consists of a series of large to small-scale gullies and hollows.Different size and scale of ripples are also found in local positions.By contrast,outside the deep trough,smooth seafloor and small-scale gullies appear alternately regularly.Ripples occurred occasionally in the near-shore water area and underwater depression on the outer edge of the trough.Combined with the analysis of bottom samples,the microrelief assemblage is decided by hydrodynamic force and sediment feature.It is noted that the direction of the flood current is coincide with that of the current indicated by the gullies,hollows and sand waves.That indicates the subaqueous microrelief could perhaps be a kind of effective index to indicate the seafloor erosion.The distribution of different types of microrelief shows that seafloor erosion is related closely with the geomorphology unit and water depth.For one thing,erosion and reformation-redeposition occurred strongly inside the deep trough indicated by gully,hollow and ripple.By contrast,relatively weak hydrodynamic condition occurred outside the deep trough,indicated by smooth seafloor.For another thing,under the similar geomorphology condition,scoured seafloor occurred in shallow water area indicated by dense small-scale gullies and smooth seafloor mainly occurred in deep water area.Overall,the seafloor is in the condition of erosion in northern Hangzhou bay subaqueous slope,indicated by the widespread eroded microrelief.
出处
《上海国土资源》
2011年第3期27-34,共8页
Shanghai Land & Resources
基金
上海市科委科技攻关计划项目(09231203300)
国家公益性行业科研专项资助项目(201011019)
