丹江口库区大孤山分汊段冲淤变化及趋势分析

Fluvial processes of Dagushan braid reach in the Danjiangkou reservoir after construction of reservoirs in the upstream

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。

Cumulative deposition usually occurs in variable backwater reach after water level rising in a reservoir. Characteristics of deposition and erosion in variable backwater reach would certainly change,or even reverse after construction of reservoirs in the upstream,owing to changes of incoming water and sediment conditions. The Dagushan braided reach of Danjiangkou reservoir was used as a research object to analysis the adjustment of erosion and deposition of braided channel in variable backwater zone before and after the construction of reservoirs in the upstream of Hanjiang River by using observed data analysis and theoretical analysis.The results show that cumulative deposition had taken place in the Dagushan braided reach during 1968-1985. The right branch took on a shrinking tendency as the result of the significantly larger cumulative deposition than the left and the deposition amount of the upper part was larger than the downstream reach because of the inflow from Duhe River. The situation of Dagushan braided reach changed from deposition to erosion,and the erosion magnitude of the right branch was significantly greater than that of the left because of significantly decrease amount of upstream incoming sediment after 2003. Dagushan braided reach will become the downstream reach of backwater area after the elevation of water level raising further at the Danjiangkou Reservoir dam. Erosion trends of Dagushan braided reach will depend on results of mutual restraints,such as the elevation of water level,decrease of sediment carrying capacity of flow and unsaturated upstream flow.