The Three Gorges Reservoir operation during small and moderate flood stage changed the process of flood runoff in middle and lower Yangtze River , which will has an obvious influence on the hydrological boundary conditions of flow diversion at the three entrances in Jingjiang reach , as well as to change the backwater effect at the export of Dongting Lake . As a result , the inflow and outflow of Dongting Lake was to be greatly changed , and the flood situation in this area varied at the same time . By using the mathematic model of the river -lake nets , and taking the inflow and outflow of Three Gorges Reservoir as the boundary conditions , the influence of the Three Gorges Reservoir operation (2009-2012 ) on water throughput of Dongting Lake during small and moderate flood stage was analyzed . The results shows that , influenced by the operation , the flow diversion of the three entrances in Jingjiang reach was reduced to certain extent , and the water level of the Yangtze River and Dongting Lake area was declined . This can effectively relieve the flood pressure of Jingjiang reach and Dongting Lake area .%三峡水库中小洪水调度运用改变了长江中下游汛期的径流过程，这一方面使荆江三口分流入洞庭湖的水文边界条件发生了变化，另一方面也改变了长江对洞庭湖出流的顶托作用，导致洞庭湖的吞吐水量发生一定的变化，区域防洪形势也随之改变。以江湖河网水流数学模型为技术手段，以三峡入库与出库流量过程为边界条件，计算分析了三峡水库2009-2012年中小洪水调度对洞庭湖吞吐水量的影响。计算结果表明，三峡水库进行中小洪水调度期间，荆江三口分流量均有一定幅度的减少，长江干流及洞庭湖区水位均有所下降，洞庭湖的出流条件有所好转，能有效缓解荆江及洞庭湖区的防洪压力。
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