长江口横沙通道冲淤变化与地形特征演变

Erosion-deposition variation and topography evolution in Hengsha Passage of Yangtze Estuary

长江口横沙通道是南北港航道的重要联络通道,研究该通道的冲淤及地形演变,对于掌握通道水动力条件及保证生产作业安全具有重要意义。采用2005~2020年长江口实测水下地形数据,利用ArcGIS建立精度为20 m×20 m的数字高程模型;通过绘制横沙通道地形图、冲淤变化图、等深线图和横断面图,对横沙通道整体地貌的演变特征和局部深坑的形成机制进行了定量及定性分析。结果表明:近期横沙通道北口出现南北长约1.85 km,最大深度达56.1 m的深坑,深坑累计扩大约380万m^(3),南延约770 m,有向深槽演变的可能。通道整体呈现“淤冲淤”的演变模式,以冲刷为主,两侧存在局部淤积,累计冲刷2880万m^(3)。深坑不断扩大的主要原因是受长兴岛北沿促淤圈围工程与青草沙水库工程建设的影响,通道北口的水动力增强,落潮流流量增加,所形成的弯道横向环流进一步加速了深坑的发育,冲刷趋势加剧。

The Hengsha Passage in the Yangtze Estuary is an important connecting passage between the North and South Channel.It is of great significance to study the erosion-deposition and topographic evolution of the passage for mastering the hydrodynamic conditions of the passage and ensuring the safety of production and operation.In this paper,the measured underwater topographic data from 2005 to 2020 in the Yangtze Estuary were used to establish a digital elevation model with an accuracy of 20 m×20 m in ArcGIS.By drawing maps about topographic,erosion-deposition change,contour and cross-sectional of the passage,the evolution characteristics of the whole landform and the formation mechanism of local pit of the passage were analyzed quantitatively and qualitatively.The results indicated that a pit with a length of 1.85 km from north to south and a maximum depth of 56.1 m,appeared at the north entrance of the Hengsha Passage recently.The pit expanded by about 3.8×10^(6) m^(3) and extended to the south by about 770 m,suggesting that it may evolve into a deep trough.The passage presented a evolution mode of‘erosion-deposition-erosion’on the whole,which was dominated by erosion.There was local deposition on both sides,and the accumulated scouring was 2.88×10^(7) m^(3).The main reason for the continuous expansion of the pit was that under the influence of reclamation engineering performed in North Changxing and the construction of the Qingcaosha reservoir,the hydrodynamic force in the north of the passage was enhanced,and the flow of the ebb current was increased,which further accelerated the development of the pit.