1973～2017年扬中市江岸冲淤遥感监测及古河道塌江分析

Erosion and Siltation Monitoring Along the River Bank of Yangzhong City During 1973-2017 by Remote Sensing and Analyzing the Bank Collapse

江心岛沿江地区的泥沙淤积、水流侵蚀以及江堤坍塌对江心岛面积形态、滩涂围垦、航道变化、河口生态等都会产生重大影响。以长江干流第二大江心岛——扬中市为研究对象,基于遥感影像监测了1973～2017年沿江区域冲淤变化和塌江区域,结合多种资料分析变化成因。结果表明:(1) 1973～2017年扬中市沿江地区冲淤变化分3个阶段,不同阶段淤积和冲蚀特点鲜明;(2)经过经纬度定位,扬中市塌江区域发生在1930年扬中市主岛太平洲右侧两个江心岛之间的夹江与西南—东北向的一条古河道的交汇处;(3)塌江事件与常规水流冲刷无关,古河道出口被堵形成水压,沿江区域江底"深槽"引发"旋流"掏空底部泥沙,加上汛期后江水下泄,内外压力差加大直接引发塌江。

The sediment deposition,water erosion and bank collapse will have a great influence on the shape of Jiangxin island,the reclamation of tidal flat,the change of channel and the ecology of estuary. In this study,Yangzhong,the second large island of the Yangtze River is taken as the research object. The erosion and siltation along the river bank of Yangzhong during 1973 and 2017 and the bank collapse in 2017 are monitored by remote sensing images. Furthermore,the reasons of dynamics are discovered by combining multiple data. Results show that:( 1) the erosion and siltation along the river bank of Yangzhong are divided into three stages and characteristic differences of different stages are obvious;( 2) after position identification,the bank collapse of Yangzhong is located in the intersection of two ancient rivers. One of them is on the right side of Taiping Island,the other is nearby it and in the southwest to northeast direction;( 3) There is no obvious relationships between bank collapse and water erosion. Blocked ancient river outlets generate water pressure and grooves in river bottom induce rotational water flow then carry off sediment. In addition,river discharge after flood season aggravates the water pressure and then results in bank collapse directly.