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由于水位的抬升,变动回水区河段一般会发生累积性淤积,而在上游修建水库后,由于来水来沙条件的变化,变动回水区河段的冲淤特性会发生变化,甚至出现逆转。以丹江口水库大孤山分汊河段为例,采用实测资料分析与理论分析相结合的方法,对比分析了上游建库前后不同时段变动回水区分汊河段的冲淤调整及其内在机理。结果表明,1968-1985年大孤山分汊段发生累积性淤积,右汊汊道内累积性淤积显著大于左汊,呈萎缩之势,支流堵河的入汇使得右汊堵河口以下淤积幅度小于右汊口门段。2003年以后,上游来沙量大幅减少,大孤山分汊段由累积性淤积转为冲刷,且右汊冲刷幅度显著大于左汊;丹江口水库坝前水位抬高之后,大孤山分汊河段成为变动回水区的下段,该河段的冲淤变化趋势将取决于水位抬高、挟沙能力下降与上游来流不饱和输沙共同作用的结果。
Due to the elevation of water level, cumulative siltation will occur in the fluctuating backwater section, and after the reservoir is built in the upper reaches, the scouring and silting characteristics of the fluctuating backwater section will change or even occur due to the change of incoming water and sediment conditions reverse. Taking the Dagushan section of Danjiangkou Reservoir as an example, this paper analyzes and analyzes the relationship between the scouring and silting in different sections of the backwater and the internal mechanism before and after the upstream reservoir construction by using the combination of measured data and theoretical analysis. The results showed that accumulative sedimentation occurred in the Dagushan section of the Dagushan Mountains from 1968 to 1985, and accumulated sedimentation in the right princes tract was significantly larger than that in the left princes. The sedimentation rate of the tributaries blocked by the tributaries was less than Right 汊 mouth door section. After 2003, the amount of sediment in the upper reaches of the Dagushan Reservoir dropped drastically. The Dagushan segment shifted from accumulative siltation to erosion and the erosion amplitude of the right 汊 was significantly greater than that of the left 汊. After the water level in front of the Danjiangkou Reservoir was raised, The segment becomes the lower part of the fluctuating backwater zone. The trend of scouring and silting in the reach will depend on the elevation of the water level and the decrease of sediment carrying capacity as a result of the interaction of unsaturated sediment transport in the upstream.