三峡建库前后长江中游河道输沙率变化分析

Changes in Sediment Transport Rate in the Midstream of Yangtze River Before and After the Construction of Three Gorges Reservoir

三峡建库后,水库下游河道含沙水流长期处于严重次饱和状态,输沙由相对平衡状态转变为不平衡状态,输沙强度较自然条件下发生显著变化。根据三峡水库蓄水运用前后(1992—2017年)长江中游主要水文站断面、床沙与水文资料,从输沙率变化、床沙粒径变化、平滩流量等角度研究长江中游河道复式断面输沙强度问题,得出以下结论:三峡水库蓄水运用后,进入下游河道的泥沙大幅度较少,长江中游沿程水文站同流量级输沙率明显减少;床沙粒径沿程出现不同程度的粗化,其中荆江河段粗化最为明显,螺山至武汉河段略有粗化;螺山站和汉口站在自然条件下平滩流量附近输沙强度出现峰值,对应的水流挟沙能力为极大值。

After the construction of the Three Gorges Reservoir(TGR),sediment-containing flow in the downstream channel of the reservoir had been in a severe sub-saturation state for a long time.The sediment transport changed from a relative equilibrium state to an unbalanced state,and the sediment transport intensity varied significantly compared with that in natural condition.Based on the cross sectional data,bed sediment and hydrological data of major hydrological stations in the midstream of the Yangtze River before and after the operation of the TGR(1992-2017),we looked into the sediment transport intensity of compound cross sections from the perspectives of sediment transport rate,bed sediment particle size,and bankfull discharge.We found that after the impoundment operation of TGR,the sediment that enters the downstream channels reduced remarkably,and the sediment transport rate of the same flow level at hydrologic stations along the midstream of Yangtze River decreased obviously.The bed sediment was coarsened in different degrees along the river.Such coarsening was most obvious in the Jingjiang reach and less obvious in the Luoshan-Wuhan reach.At hydrologic stations of Luoshan and Hankou,the sediment transport intensity in the adjacent of bankfull discharge reached the maximum under natural conditions,and the corresponding sediment carrying capacity reached peak.