水流挟沙力变化是研究水库下游悬沙输移及河道演变的核心问题之一。以长江中游沙市—汉口沙质河段为研究对象,引入韩其为非均匀悬移质不平衡输沙中水量百分数、挟沙能力级配等概念,阐释了三峡建库前后非均匀悬移质挟沙力变化及其影响因素。建库后,沙市、监利站各流量级下床沙转为挟沙力的水量百分数均明显增加,螺山、汉口站分别超过临界流量30 000 m3/s和35 000 m3/s时,床沙转为挟沙力的水量百分数有所增加;沙市—城陵矶河段水流挟沙力减小程度大于城陵矶—汉口河段,其中沙市—城陵矶河段＜0.125 mm粒径组挟沙力大幅减小,城陵矶—汉口河段＜0.25 mm粒径组挟沙力减小。沙市—城陵矶河段水流挟沙力减小主要受挟沙力平均沉速ω*变化影响,城陵矶—汉口河段水流挟沙力减小受挟沙力平均沉速ω*和挟沙力判数U3/h的共同影响,其中螺山、汉口站分别不超过临界流量30 000 m3/s和35 000 m3/s时,挟沙力判数U3/h的贡献率较大。
Abstract
Sediment carrying capacity (SCC) is a crucial factor in the study of suspended sediment transport and channel evolution in the downstream of reservoirs. This study focuses on the river reach from Shashi to Hankou in the midstream of Yangtze River. By introducing two concepts in the non-equilibrium suspended sediment transport theory proposed by Han Qiwei, namely, the percentage of flow discharge which changes bed load into suspended load, and the particle gradations of sediments carried in flows, we examined the changes, and factors affecting the changes in the non-uniform suspended sediment carrying capacity after the construction of the Three Gorges Dam (TGD). Following the completion of TGD, Shashi and Jianli stations witnessed a significant increase in the percentage of flow discharge under various discharge levels. Specifically, when the discharge exceeded 30 000 m3/s at Luoshan station and 35 000 m3/s at Hankou station, the percentage of flow discharge increased. Shashi-Chenglingji reach experienced a more pronounced decrease in sediment carrying capacity than Chenglingji-Hankou reach. Moreover, the carrying capacity for sediment particles smaller than 0.125 mm declined significantly in Shashi-Chenglingji reach, while particles smaller than 0.25 mm reduced in Chenglingji-Hankou reach. The reduction of sediment carrying capacity in Shashi-Chenglingji reach is primarily attributed to the influence of ω* (which is the average settling velocity of sediments), while in Chenglingji-Hankou reach, it is jointly affected by U3/h (a factor of SCC) and ω*. Notably, U3/h plays a more prominent role when the critical discharge at Luoshan and Hankou does not exceed 30 000 m3/s and 35 000 m3/s, respectively.
关键词
水流挟沙力 /
不平衡输沙 /
非均匀悬移质 /
三峡水库 /
长江中游
Key words
sediment carrying capacity /
non-equilibrium sediment transport /
non-uniform suspended load /
Three Gorges reservoir /
midstream of Yangtze River
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基金
国家自然科学基金长江水科学研究联合基金项目(U2240206)
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