三峡水库运行下洞庭湖盆冲淤过程响应与水沙调控阈值

以1951-2011 年洞庭湖区及荆江段干流主要控制站实测径流输沙量资料为依据，分析三峡水库不同蓄水阶段及不同调度方式下洞庭湖盆冲/淤响应，并提出上游来水来沙调控阈值。结果表明：① 荆南三（四）口流量与枝城站流量、荆南三（四）口输沙率存在极显著正相关（p < 0.0001），决定系数r2分别为0.859 及0.895。② 与三峡水库蓄水运用前（1999-2002）相比，一、二期蓄水阶段及全面试验性蓄水阶段（2008.10-2011.12）洞庭湖盆年均冲淤量由+4796.4×10⁴ t 依次递减为+684.1×10⁴ t、+449.8×10⁴ t 及-559.6×10⁴ t，湖盆冲淤率由+70.25%分别降至+31.13%、+23.56%及-42.64%。③ 预泄调度及蓄水调度期，湖盆泥沙均由以淤积为主转变为以冲刷为主，防洪补偿调度期湖盆泥沙表现为淤积，而在补水调度运用期则表现为冲刷。④ 洞庭湖盆处于冲/淤临界平衡状态时的荆南三口平均流量、输沙率及含沙量分别为970.81 m³/s、466.82 kg/s 及0.481 kg/m³。并认为，为增强湖泊调蓄功能，必须进一步优化三峡水库调度方式，合理调控下泄水沙量。

Silting/scouring process responses of Dongting Lake basin to the operations of TGR and thresholds of water-sediment regulation

Based on measured runoff and sediment discharge rate of major control stations in the Dongting Lake basin and the Jingjiang River section, Yangtze River, from 1951 to 2011, this paper analyzes silting/scouring process responses of the Dongting Lake basin to different impoundment phases and different dispatching modes of the Three Gorges Reservoir (TGR). Results are shown as follows: (1) Significant correlations were found between flow rate of the Zhicheng Station and flow rate of the Three (Four) Outlets of the Southern Jingjiang Rivers (r²=0.859, p<0.0001), flow rate and sediment deliver rate of the Three (Four) Outlets (r²=0.895, p<0.0001), indicating that flow rate and sediment deliver rate of the Three (Four) Outlets were strongly influenced by upstream Yangtze River flow rate. (2) Compared with period before operation of the TGR (1999-2002), sediment silting/scouring amount of the Dongting Lake basin during the TGR impoundment phases I, II and the TGR in comprehensive operation phase (2008.10-2011.12) dropped from +4796.4×10⁴ t to +684.1×10⁴ t, +449.8×10⁴ t, -559.6×10⁴ t, and sediment silting/scouring rate dropped from +70.25% to + 31.13%, +23.56%, -42.64% successively. The results present notably positive effects due to operation of the TGR. (3) During pre-discharge dispatch and water-storage dispatch period, the lake basin changed from silting to scouring mode. For flood-storage dispatch and water-supplement dispatch period, the Dongting Lake basin was mainly controlled by silting and scouring processes, respectively. (4) The calculated optimum thresholds of annual mean flow rate, sediment transport rate and sediment concentration of the Three Outlets were 970.81 m³/s, 466.82 kg/s and 0.481 kg/m³, respectively, while the Dongting Lake basin were under the state of neither silting nor scouring. The thresholds could provide practical references for operation regulation of the TGR.