Effects of 175 m experimental operation of the Three Gorges Reservoir on the storage capacity of Lake Dongting

长江干流与洞庭湖存在复杂的并联型分汇关系，当三峡水库调度改变长江径流过程时，会引起洞庭湖年内槽蓄量的变化，对于洞庭湖地区防洪、水资源配置和水环境保护产生显著的影响.本文建立了枝城至螺山站的荆江-洞庭湖水流模型，利用2008-2017年的三峡水库实际调度日数据，分析有、无三峡水库调度两种情况下洞庭湖槽蓄量的变化过程，同时利用建库前和近期的水位流量关系反映河道过流能力，分析了河道调整的影响.结果表明：由河道调整引起的槽蓄量变化在汛前消落期、汛期、汛末蓄水期和枯水期分别为-3.06%、0.12%、-0.01%和-13.31%.有三峡水库影响情况下，汛前消落期由于荆江三口进入洞庭湖的多年平均总径流增加23.94%，洞庭湖出口处城陵矶多年平均水位升高0.53 m，阻碍了洞庭湖出流，洞庭湖多年平均槽蓄量增长13.30%；汛期由于荆江三口分流量减少3.54%，城陵矶水位降低0.02 m导致出湖流量增多，因此洞庭湖多年平均槽蓄量减少0.20%；在汛末蓄水期，荆江三口分入洞庭湖的多年平均总径流量减少37.18%，城陵矶多年平均水位降低1.33 m，导致出湖流量增多，因而洞庭湖多年平均槽蓄量减少27.74%；在枯水期，荆江三口多年平均总径流量增加5.61%，城陵矶多年平均水位上升0.07 m，最终洞庭湖多年平均枯期槽蓄量增加2.96%.;Stem stream of Yangtze River and Lake Dongting have complicated relation of diffluence and confluence. Operation of the Three Gorges Reservoir leads to intra-year variation of runoff process and storage capacity of Lake Dongting, which is significant and profound for flood control, water resource allocation and water environmental protection in Lake Dongting area. This paper built a flow model of Jingjiang River and Lake Dongting from Zhicheng to Luoshan Station which involves three modules:the flow-split module of Jingjiang River, the main stream module and the Lake Dongting module. Based on the actual operational data of the Three Gorges Reservoir, variation of the storage capacity of the Lake Dongting with and without the influence of the Three Gorges Reservoir during 2008-2017 were calculated and analysed. The results show that the variation of the storage capacity of the Lake Dongting caused by river topography is -3.06%, 0.12%, -0.01% and -13.31% in seasons of pre-flood and main-flood, post-flood and dry period, respectively. Under the influence of the Three Gorges Reservoir, the multi-year average total runoff diverted from Jingjiang River (MARJ) increased by 23.94% in the pre-flood period, and the multi-year average water level at Chenglingji Station (MAWC) increased by 0.53 m, which hindered the flow of Lake Dongting into the Yangtze River. The annual average water storage of Lake Dongting (AWD) increased by 13.30%. In main-flood season, the MARJ and MAWC decreased by 3.54% and 0.02 m respectively, which resulted in the increase of outflow. Therefore, the multi-year AWD decreased by 0.20%. In post-flood season the MARJ and MAWC decreased by 37.18% and 1.33 m respectively, resulting in an increase in the discharge of the lake and a reduction 27.74% of the AWD. During the dry season, the MARJ and MAWC increased by 5.61% and 0.07 m respectively, resulting in the decrease of outflow from the Lake Dongting. The AWD increased by 2.96% over the years.