1956—2020年荆江三口径流变化特征及水库补水效果

荆江三口的分流对于洞庭湖区的水资源、河湖生态系统安全等均具有重要的影响.受到人类活动和气候变化双重影响，荆江三口分流发生显著变化，亟需明确其变化特征及适应性对策.基于实测数据分析了荆江三口径流变化特征，采用数值模拟评估了水库不同下泄方案对推迟荆江三口断流的影响.结果表明：荆江三口年径流量呈递减趋势，2003年以后分流比没有趋势性变化；相比1981—2002年，2003—2020年荆江三口径流汛期和退水期径流分别减少26%和40%，枯水期和涨水期分别增加了194%和17%.2003年以后，沙道观站长断流（历时>60 d）持续时间和短断流（历时≤60 d）发生频次均有所增加；弥陀寺站长断流时间有所减少，而短断流时间和频次显著增加；康家岗和管家铺站在长断流时间有所增加，短断流时间有所增加，频率有所减少.在枯水年情况下，水库增加下泄时间与推迟三口断流时间比不超过1.2，补水效率不超过0.28%，因此不推荐通过水库增加下泄流量方法推迟弥陀寺和管家铺站断流.

Characteristics of runoff in the three outlets along Jingjiang River and the influence of water supplement by the reservoirs during 1956-2020

The runoff in the three outlets of Jingjiang River had an important impact on water resources and river and lake ecosystem security in Lake Dongting area. Due to the influence of human activities and climate change, the runoff in the three outlets of Jingjiang River had changed significantly. Based on the observed hydrological data, the characteristics of runoff in the three outlets along Jingjiang River was analyzed, and the influence of water supplement of the reservoir on the cutoff in the three outlets along Jingjiang River was evaluated by numerical simulation. The results indicated that the annual runoff in the three outlets along Jingjiang River showed a decreasing trend from 1981 to 2020, whereas the diversion ratio showed no significant change after 2003. Compared with 1981 to 2002, the runoff of the three outlets of Jingjiang River from 2003 to 2020 decreased by 26% and 40% in the flood period and the decreasing stage period, respectively, while that of the dry period and the rising stage period increased by 194% and 17%, respectively. The number of days of long-break and the frequency of short-break both increased for Shadaoguan station after 2003. For Mituosi station, the number of long-break days decreased but that of short-break increased. The number of days of long-break for Kangjiagang and Guanjiapu stations increased although the number of days of short-break increased with decreased frequency. In the dry year, the number of days with increasing discharge was only 1.2 times of the days which were influenced by the replenishment, with the replenishment efficiency no more than 0.28%. Hence, we do not recommend to postpone the cutoff of Maituosi and Guanjiapu stations by increasing the discharge of the reservoirs.