近30年来长江河口南港冲淤变化与微地貌特征

Three Decades of Morphological Changes and Micromorphology Features in the South Channel of the Yangtze River Estuary

利用多波束测深系统在2015年2月1~7日期间测量长江河口南港河段的河槽地貌形态,获取高精度的床面微地貌资料,结合南港河槽底质资料和1992~2019年的海图水深数据分析近期南港河段的河槽演变特征,探讨人类活动对南港河槽演变的影响.结果显示:在流域大型工程尤其是三峡大坝的影响下,长江流域到达河口的来沙量锐减,导致南港河段由河槽淤积状态(1992~2002年)转变为河槽侵蚀状态(2002~2019年);近期南港河槽上存在着常见床面微地貌形态(平滑床底、沙波和冲沟)和人为强干扰下的床面形态(疏浚痕和凹坑),沙波的波长、波高和沙波指数的均值分别为21.5、0.91和0.06m,与沙波有关的河槽糙率(Ks)是0.65;近期南港河段河槽冲刷和底质类型以细砂为主的环境有利于沙波尺度的增大和沙波发育的空间范围向下游推进.

The study investigated micromorphology of the South Channel of the Yangtze River Estuary using multi-beam bathymetric data measured during February 2015.Digitized bathymetric data during 1992~2019 were also used to access long-term morphological changes of the riverbed and how the changes were affected by human activities.Results show that the channel bed changed from aggradation during 1992~2002 to degradation during 2002~2019 due to significant decrease of sediment supply caused by the Three Gorge Dam.There are three common bedforms in natural rivers in the South Channel(i.e.,smooth surface,gully and dune).We found two micromorphology usually formed under human intervention which are hollow and dredging marks.The average length,height,and height to length ratio of the dunes are 21.5,0.91,and 0.06 m,respectively.The bed roughness(Ks)associated with the dunes is 0.65.Severe channel erosion and coarse sand supply may contribute to the growth of the dunes and the downstream movement of the dune zone.