中文摘要：

受到弯曲与分汊河道的输水输沙特性的共同作用,弯曲分汊河道的河床演变过程复杂。以长江中游监利河段为例,选取9期遥感影像数据,利用Envi和Arcgis解译并提取河道的平面形态特征。结果表明,在1987-2014年间,监利两汊道宽度变化显著,左汊宽从1 041m减少至340m,右汊宽从632m增大至1 531m;与此同时,江心洲最大长度增加近900m,平均宽度缩窄200余m。在1995年前后,监利河道的水面宽度增大,江心洲的长宽比从3.59增加至4.32,河道发生主支汊易位。通过对监利站的水沙过程进行分析发现,监利汊道发生主支汊易位可能是由流量自80年代后进入中高水期而引起的水动力轴线不断右移所致。同时,为了适应来水来沙由＂沙多水少＂向＂水多沙少＂转变,监利河段的平面形态从减小江心洲宽度和增加河道水面宽度这两个方面进行调整,以减少河道的输沙能力,维持合理的输沙效率。

英文摘要：

The conveyance of water and sediment produce complex channel planform of the meandering and anabranching river pattern dominated by not only second current due to centrifugal force in the flow but also the dynamic characteristics of bifurcation and confluence regions. Nine landsat images acquired in 1987, 1990, 1994, 1996, 2000, 2003, 2006, 2010 and 2014 on Jianli reach in the middle Yangtze River were selected. Remote sensing image processing techniques and GIS were applied to interpret and extract the channel plan- form information. The results show that there are obvious changes in the channel width of two branches from 1987 to 2014, with the width of the left branch reduced from 1041m to 340 m and that of the right branch in- creased from 632 m to 1531 m. The maximum length of the island increased about 900m and the average width decreased about 200m, with the mean length-width ratio of the island increased from 3.59 to 4.32. During 1994 to 1996, the main branch switches from left channel to right channel. The yearly flow discharge and sedi- ment transport rate from 1951 to 2013 were used to explore the mechanism of channel planform evolution. It is found that the switches of the main channel from one to another may be caused by the increase of the flow dis- charge from 1980s which lead to the flow dynamic axis moving right. In order to maintain an appropriate conveyance of water and sediment, Jianli anabranching planform responds to the change in the matching regimes of flow discharge and sediment transport rate from ＇high-sediment and low-water＇ regime to ＇high- water and lowsediment＇ by narrowing the island width and increasing the surface width.