三峡水库蓄水后荆江三口分流能力变化原因初探

Causes of water diversion capacity change at three outlets of Jingjiang River after impoundment of Three Gorges Reservoir

荆江三口分流分沙是驱动江湖关系演变的重要因素之一,研究三峡水库蓄水运用后荆江三口分流能力变化机制具有重要意义。基于长系列水文资料分析,探究了三峡水库蓄水运用前后荆江三口口门附近干流及三口进口段水面比降、口门水位变化与三口分流能力变化之间的驱动-响应机制。研究表明,三峡水库蓄水运用后荆江三口口门附近干流水面比降以增大为主;同流量下三口口门水位均有所下降,太平口水位降幅最大;松滋口、太平口洪道进口段水面比降均有所下降,但藕池口有所增加;太平口附近干、支流水面比降变化相反,对分流比的影响一致;藕池口附近干、支流水面比降同增或同减,对分流比的作用相互抵消,分流比主要朝干支流水面比降中变化幅度相对较大的方向变化;影响松滋口分流能力的因素众多,调整机制更为复杂,需进一步深入研究。

The diversion of water and sediment through the three outlets from the Jingjiang River is one of the key factors driving the evolution of the relationship between the Yangtze River and the Dongting Lake.It is thus of great scientific significance and application value to study the change mechanism of the water diversion capacity(WDC)at the three outlets after the impoundment of Three Gorges Reservoir.Based on the analysis of long-term hydrological data,this paper explored the driving-response mechanism between the water-surface gradient of the Jingjiang River and its three tributaries,the water levels changes and the water diversion capacity changes at the three outlets.The study found that after the impoundment of the Three Gorges Reservoir,the water-surface gradient of the Jingjiang River at each outlet increased at most discharge levels.The water level,under the same discharge,decreased at each outlet,and the Taiping Outlet decreased most.The water-surface gradient at the entrances of Songzi Outlet and Taiping Outlet declined at all discharge levels,while the water-surface gradient at the entrance of Ouchi Outlet increased.The water-surface gradient changes at the main stream and tributary near Ouchi Outlet were the opposite,and have the same effect on diversion ratio.The water-surface gradient changes at the main stream and tributary near the Ouchi Outlet have same tendency,which cancels each other’s effect on the diversion ratio.Diversion ratio develops to the side where the main stream or tributaries have relatively large water-surface gradient.There are many factors affecting the water diversion capacity of the Songzi Outlet,and the adjustment mechanism is more complicated,which needs further study.