A varied class method is applied to calculate the effective discharges and their variations after the Three Gorges Dam (TGD) construction based on the mean daily flow discharge and suspended sediment concentration field data from 1981 to 2016. For comparison, the bankfull discharges are also determined according to the cross-section profiles and flow discharge-stage relations. Our results show that a bimodal effective discharge curve usually exists at the fixed sites, which generates two effective discharges (Q_e1 and Q_e2) within the moderate flow range. Under the quasi-equilibrium circumstances of the pre-dam period, effective discharges are closely related to the mean annual runoff, with a narrow range of regional variations in occurrence frequency. Our analyses draw the conclusion that the relatively higher unsaturation degrees of the pre-dam effective discharges caused by dam interception and riverbed coarsening are the primary cause of the increase in effective discharges from Yichang to Shashi, while the more frequent low and medium discharges due to flow regulation drive the decrease in effective discharges from Jianli to Datong. The slightly elevated flood levels and descending bankfull levels collaboratively result in the decrease of bankfull discharges from Yichang to Shashi, while the lowered bed elevation causes the increase in bankfull discharges from Luoshan to Datong. Overall, the bankfull discharge in the Middle and Lower Yangtze River is larger than effective discharge and approaches the 1.5- year recurrence interval discharge.

基于1981年至2016年的平均日流量流量和悬浮泥沙浓度场数据，采用变类方法计算三峡大坝（TGD）施工后的有效流量及其变化。为了进行比较，还确定了满溢流量根据横截面轮廓和流量排放阶段的关系。我们的结果表明，固定位置通常存在双峰有效放电曲线，该曲线会产生两个有效放电（Q _e1和Q _e2）在中等流量范围内。在大坝前期的准平衡条件下，有效流量与年均径流量密切相关，发生频率的区域变化范围很窄。我们的分析得出的结论是，由大坝拦截和河床粗化引起的大坝前有效排水量的相对不饱和度较高，是导致宜昌至沙市有效排水量增加的主要原因，而中，低端排水量则更为频繁。流量调节促使从建里到大同的有效流量减少。洪水位的略微升高和河岸水位的下降共同导致宜昌至沙市的河岸水流量减少，较低的河床高程导致罗山至大同的河岸流量增加。总体而言，长江中下游的河滩流量大于有效流量，并接近1.5年的复​​发间隔流量。