荆江三口分流分沙及洞庭湖出口水沙输移的变化规律

荆江三口分流分沙及洞庭湖出口水沙输移的变化，不仅关系到洞庭湖区防洪、航运及水资源利用等，而且影响到长江与洞庭湖关系的变化趋势。利用三峡工程蓄水前后的最新实测资料分析荆江三口分流分沙及洞庭湖出流水沙变化规律，得到以下成果与结论：三峡工程蓄水以来荆江三口分流分沙比无明显变化趋势，但荆江三口分沙量大幅度地减少，其中三口五站断流天数也无明显变化，除弥陀寺、康家港断流时长江干流临界流量略有减少外，其它三站干流临界流量均变化不大。三峡工程蓄水后七里山年均输沙量减少幅度不大，但洞庭湖排沙比显著增大，甚至部分年份洞庭湖排沙比超过100%。此成果对于深入研究江湖关系调整规律和预测长江与洞庭湖的变化趋势均具有重要意义。

Variation of Split-Flow and Sediment Diversion at the Three Outlets along Jingjiang River and Water and Sediment Transport at the Outlet of Dongting Lake

The variation of flow and sediment diversion at the three outlets along Jingjiang river and the change of water-sediment transport at the outlet of Dongting Lake are studied on the basis of field data before and after the impoundment of Three Gorges Reservoir. The above changes influence the flood control, navigation and water resources utilization of Dongting Lake, and affect the relationship between the Yangtze River and the Dongting Lake as well. Results indicate that ratios of split-flow and sediment diversion at the three outlets saw no obvious change since the impoundment of the reservoir; whereas the amount of sediment diversion reduced by a large margin. The days of zero-flow at five stations barely changed, with the critical flow in mainstream Yangtze River reduced slightly during zero-flow days at Mituosi station and Kangjiagang station, and changed little at the other three stations. The average annual sediment load had no big decrease at Qilishan station, while the sediment delivery ratio of Dongting Lake increased remarkably, larger than 100% in some specific years.