三峡水库蓄水运用后,清水下泄使得坝下游宜枝河段发生显著冲刷,河道过流能力也相应调整。宜枝河段(包括宜昌及宜都两河段)断面形态复杂,且过流能力沿程差异较大,河段平均的平滩流量更能反映其综合过流能力。采用基于对数转换的几何平均与断面间距加权平均相结合的方法,分别计算了宜昌及宜都河段2002—2013年各年汛后的平滩流量,分析了河床冲淤变化对河段平滩流量的影响,同时还建立了两河段平滩流量与前5 a汛期平均水流冲刷强度的经验关系。结果表明当河段冲刷时,平滩流量增大,反之则减小;宜昌河段平滩流量与水流强度相关性系数较低,为0.64,而在宜都河段为0.94,表明宜都河段对上游水沙条件变化的响应较宜昌河段更为显著。

A sharp reduction in sediment load has caused a significant process of channel degradation along the Yichang-Zhicheng Reach after the operation of the Three Gorges Project (TGP), especially in the adjustment of flood discharging capacity. In view of the complicated cross-sectional profiles and the great longitudinal variability in flood discharging capacity, the reach-scale bankfull discharges in the reaches of Yichang and Yidu from 2002 to 2013 were estimated using a combination of geometric average and weighted average method. The effect of channel erosion and deposition on the reach-scale bankfull discharge in each reach was investigated. In addition, empirical relationships were established between the reach-scale bankfull discharge and the previous five-year average fluvial erosion intensity during flood seasons for these two reaches, and it was found that bankful discharge increased with erosion, and decreased with deposition; the correlation between bankful discharge and flow intensity in Yichang was 0.64, whereas in Yidu it was 0.94, indicating that the response of bankfull discharge to the altered flow and sediment regime in the Yidu reach was more remarkable than that in the Yichang reach.