三峡建库后沙市—汉口河段悬移质分组冲淤变化规律

Variation of grouped suspended sediment deposition and erosion in Shashi—Hankou reach after the construction of the Three Gorges Dam

水库下游河道冲淤调整是一个长期复杂的过程,对防洪、航运、生态等均会产生一定影响。为探究长江中游沙市—汉口河段演变趋势并为不利变化的防控提供参考,分析了三峡建库后悬移质分组冲淤时空变化规律:建库后,沙市—监利河段各粒径组泥沙均发生冲刷,沙市流量为10000~25000 m^(3)/s时,0.125~0.250 mm粒径组泥沙冲刷量最大;以0.125 mm为粗细颗粒分界粒径,监利—螺山段呈现汛期、蓄水期“粗淤”而枯水期、消落期“冲细”现象;螺山—汉口段各粒径组泥沙均发生冲刷,且流量越大冲刷量越大。在此基础上,通过建立流量—分组输沙量关系并根据水流挟沙力公式,发现建库后沙市—监利、螺山—汉口河段冲淤受泥沙、水力因素共同作用,其中泥沙因素对沙市—监利河段影响大于螺山—汉口河段;监利—螺山河段“淤粗冲细”主要受含沙量恢复程度的影响,与上游河床冲刷补给及本河段粗、细颗粒泥沙交换有关,反映了冲刷条件下河道通过水流挟沙能力级配调整加大输沙能力。

The adjustment of scouring and silting downstream of reservoirs is a long-term complex process,which has a certain impact on flood protection,navigation and ecology.To explore the evolution trend of Shashi—Hankou reach in the middle reach of the Yangtze River and provide a reference for the prevention and control of adverse changes,the temporal and spatial changes of deposition and erosion of grouped suspended sediment after the construction of the Three Gorges Dam(TGD)are analyzed.After the construction of TGD,the sediments of each particle size group in Shashi—Jianli reach are eroded;and the 0.125—0.250 mm particle size group has the largest amount of sediment erosion when the discharge at Shashi station is 10000—25000 m^(3)/s.Taking 0.125 mm as the boundary particle size of coarse and fine particles for the Jianli—Luoshan reach,the reach is characterized by"coarse deposition"in flood season and storage period,and"fine erosion"in low water season and pre-flood falling period.The sediments of each particle size group in the Luoshan—Hankou reach are eroded,and the larger the discharge,the greater the amount of erosion.On this basis,by establishing the relationship between discharge and sediment of different particle size groups and analyzing the sediment carrying capacity formula,it is found that after the construction TGD,the scouring and silting of the Shashi—Jianli reach and the Luoshan—Hankou reach are affected jointly by sediment and hydraulic factors,and the impact of sediment factors on the Shashi—Jianli reach is greater than that on the Luoshan—Hankou reach.At the same time,the“coarse deposition and fine erosion”in the Jianli—Luoshan reach is mainly affected by the recovery degree of sediment concentration,which is related to the scour replenishment of the upstream riverbed and the exchange of coarse and fine sediments in this reach,reflecting that the sediment carrying capacity of the river channel under scour condition can be increased by grading adjustment.