三峡水库运行后荆江段河湾平面形态演变特征

River bend planform evolution in Jingjiang reach of the Yangtze since Three Gorges Reservoir operation

目前对三峡水库运行后下游水文泥沙特性变化、河道冲刷与崩岸等问题已有认识,但对河湾平面形态演变还少见论述。本项研究基于研究区枯水期遥感影像,分析了三峡水库运行10余年来荆江段枯水河湾平面形态的演变特征。结果表明,枯水河湾的中心线长度、凸岸长度、凹岸长度、弯曲率和中心轴长度存在显著变异,以下荆江段的变异程度更大,凸、凹岸及上、下荆江段在演变过程上存在非同步性。上荆江段凹岸先于凸岸发生显著变异,且平面形态演变以凹岸冲刷延伸占主导作用,下荆江段凸岸先于凹岸显著变异,并以凸岸冲刷收缩占主导。大部分河湾尤其在下荆江,表现为面积、平均宽度明显增加,而中心线长度、弯曲率与中心轴长度减小,河湾发展具有河道冲刷展宽但弯曲退缩的特征。还讨论了平面形态演变与凸、凹岸冲淤变化的关系。

Effects of the Three Gorges Reservoir （TGR） on its downstream hydrologic and sediment regimes and riverbed erosion have been much addressed, but planform evolution of river bends was less known. In this work, we studied the planform evolution of river bends in the Jingjiang reach of the middle Yangtze since TGR operation using three multi-temporal remote sensing images acquired in low water period. Results showed that （1） significant changes occurred in central-line length, convex bank length, concave bank length, sinuosity, and central-axis length of the bends, （2） that the changes in the lower Jingjiang were more remarkable, and （3） that the evolution of convex and concave banks as well as the evolution in the upper and lower Jingjiang were non-synchronous. In the upper Jingjiang, changes in concave banks occurred prior to those in convex banks, and erosion on concave banks and their extensions played a leading role in the evolution; while in the lower reach, erosion on convex banks and their shrinking were dominant and prior to the occurrence of concave bank erosion. Most of the river bends, especially those in the lower Jingjiang, showed evident increases in bend area and average width and remarkable decreases in central-line length, sinuosity and central-axis length. All this implies that since TGR operation, river bend curving has been weakening and river channels have been broadening. The relation of planform evolution to changes in concave and convex banks is also discussed in this paper.