近期长江口北槽河段河槽演变对人类活动的响应

利用多波束测深系统在2014年11月期间测量长江口北槽河段的河槽地貌形态,获取高精度的床面微地貌资料,结合北槽河槽底质资料和1979～2019年期间的海图水深数据分析近期北槽河段的河槽演变特征,探讨人类活动对北槽河槽演变的影响。结果表明:在人类活动的强烈干扰下,1979～2019年的40年期间,北槽河段(上段至口外段)以河槽侵蚀为主,净冲刷的泥沙体积达0.36×10~(8 )m~3,平均每年冲刷0.009×10~(8 )m~3,北槽河段水深增大可能加剧了盐水入侵;在流域大型工程尤其是三峡大坝的影响下,长江流域输送到河口的沙量持续减少,致使近期严重的河槽侵蚀发生北槽河段口外段;在深水航道治理工程的影响下,近期北槽河段(上段至下段)总体上呈现主槽侵蚀、两岸淤积和深水航道泥沙回淤严重的特征;北槽床面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、凹坑和洼地);在北槽中段和下段发育的沙波的波长的均值分别为39.41和11.11 m,波高均值分别为0.48和0.33 m,与沙波有关的河槽糙率(Ks)的值分别是0.14和0.19,且此次观测到的小范围沙波为首次在北槽河段(长江河口最大浑浊带)观测到的沙波微地貌。

Morphological Change of North Passage of the Yangtze Estuary in Response to Human Activities

Abstract：Multi-beam bathymetric measurements made during November 2014 were used to investigate micromorphology of the North Passage of the Yangtze River estuary. The physical properties of the micromorphology were assessed by grain size analysis of bottom sediment samples collected. The morphological changes of the riverbed channel were assessed by the digitized bathymetric data. Results show that channel erosion occurred in the North Passage from 1979 to 2019 because of human activities. net volume loss and mean annual net volume loss reached 0.36 × 108 m ³ and 0.009 × 108m ³ yr ^-1 in the North Passage. Increase of depth water in the North Passage may aggravate the saltwater intrusion. The sediment supply at Datong Hydrological Gauging Station showed a declining trend because of the influence of the Three Gorge Dam (TGD), which may have contributed to channel erosion of the outer estuary. Channel erosion occurred in main channel and distinct accretion occurred in the northern side and southern side because of the Deepening Waterway Project. In addition to three kinds of common bedforms: smooth surface, gully and dune, there are also two kinds of micromorphology under the human intervention: hollow, low-lying land and dredging mark. The mean length and mean height of dunes in the middle reach is 39.41 and 0.48 m, respectively, and the mean length and mean height of dunes in the lower reach is 11.11 and 0.33 m, respectively. The value of bed roughness (ks) associated with the dunes in the middle reach and lower reach is 0.14 and 0.19, respectively. A small area of dunes in the middle and lower reaches of the North Passage was observed for the first time in the turbidity maximum zone of the Yangtze River Estuary.