长江干流江苏段44年来河道冲淤变化的时空特征

Temporal-spatial Variation of the Channel in Jiangsu Reach of the Yangtze River during the Last 44 Years

通常认为气候变暖引起的海平面上升将导致下游河道的淤积,流域水土保持和水库建设引起的上游来沙量的减少将导致下游河道的冲刷。然而,长江下游河道是如何对海平面上升和上游来沙量的减少做出响应的,至今还没有直接的确凿的证据。在地理信息技术支撑下,对长江干流江苏段(约330km)5个时期1:25000～1:60000的河道地形图进行了数字化,建立了1959、1970、1985、1992和2003年河道数字地形图,对河道的冲淤变化进行了计算分析。结果表明,长江干流江苏段在1985年前后发生过明显的河道冲淤转换:由1959-1985年之间的平均淤积状态转变为1985-2003年之间的平均冲刷状态。主要原因是1985年以后该河段的上游来沙量的减少。1959-1985年之间长江干流江苏段河道的淤积过程,存在着由上游向下游推进的"顺流堆积"现象。1985-2003年之间,下段冲刷速率大于中段和上段。

River channel sedimentation in the lower reaches of the Yangtze River can be affected by both rising sea level due to global warming and the construction of reservoirs in the upper river that reduces the amount of sand discharge. To evaluate the dynamic changes of sedimentation and erosion of the Jiangsu reach of the Yangtze River （about 330 km in length） from 1958 to 2003, databases of five periods Digital Elevation Mode （DEM） of underwater topography were designed and constructed on the basis of the Jiangsu River Relief Map in 1959, 1970, 1985, 1992 and 2003 （1：25000-1：60000）. The result indicated that the main course of Yangtze River in Jiangsu Province had experienced an obvious switch from sedimentation to erosion around 1985 because of the decreasing amount of sediment yield from the upper Yangtze River after that year. The sedimentation process in the main course of Jiangsu reach of the Yangtze River demonstrated propulsive phenomena of ＂down-reach-ward accumulation＂. Between 1985 and 2003, the erosion rate of the lower segment was greater than those of the middle and upper segments. The reason is probably the bigger shortage of sediment yield due to the decrease of sediment source from the upper reach and the strengthening protection of the bank erosion in the lower reach.