荆江三口分流变化及三峡水库蓄水影响

长江中游荆江的水沙通过三口洪道分流入洞庭湖，三口分流是荆江-洞庭湖关系调整的驱动因子，为揭示其变化特征及三峡工程运用的影响，基于大量的原观数据，系统研究了近60年三口分流比的变化过程，提出其显著调整特征及诱发因素，引入径流还原计算方法，量化了三峡水库不同运用方式对三口分流量的影响幅度。结果表明:①特大洪水及重大人类活动等诱发因素作用下，三口分流比出现4~5年持续性减小的趋势调整期，之后进入分流比稳定恢复的平衡调整期；②2003-2014年，三峡水库汛前枯水补偿调度使得三口分流量年均增加8.000亿m3，汛后蓄水使得三口分流量年均减小29.00亿m3，对三口分流综合影响量为年均减少21.00亿m3，占同期三口年均分流量的4.29%。

Runoff diverted from the Jingjiang reach to the Dongting Lake and the effect of Three Gorges Reservoir

As the water and sediment of the Yangtze River are diverted at the three outlets into the Dongting Lake, the relationship of rivers and lakes in the middle Yangtze River is mainly determined by the changes of the flow diversion ratio at the three outlets (FDRTO). To reveal the variation characteristics of FDRTO, average daily discharge of hydrometric stations both in the Jingjiang reach and the diversion channels in recent 60 years are employed. Abnormal hydrological conditions and major human activities have been proved as the main factors induced the FDRTO changes. Besides, Reduction calculation of runoff at Yichang station considering without TGR water was conducted based on balance approach, by compared with the field data, the influence of TGR on the diversion flow can be estimated. The studies show that ① catastrophic flood and major human activities cause a 4 to 5-year trend-adjustment period of the FDRTO, the flow diversion ratio was continuously decreased during such period, and then became stable in the following balance-adjustment period; ② From 2003 to 2014, the runoff diverted from Jingjiang reach increased by 0.800 0 billion cubic meter every year under the low compensation operation of TGR in dry season, but decreased by 2.900 billion cubic meter every year effected by impounding water of TGR after the flood season. The comprehensive influence of TGR on the diversion flow of the three outlets is about 2.100 billion cubic meter every year, accounted for 4.29% of its total annual runoff.