城陵矶综合枢纽工程建设对洞庭湖水动力影响模拟研究

受流域降雨量偏枯以及三峡工程蓄水运行等综合影响,洞庭湖季节性干旱问题近年来日益突出.为缓解洞庭湖旱情,湖南省和湖北省政府提出了建设城陵矶综合枢纽工程.枢纽工程的建设,将改变洞庭湖水动力特征,影响湖区生态环境.该研究基于MIKE 21模型构建了洞庭湖二维水动力模型,模拟预测了枢纽工程建设前后洞庭湖湖体水位、流速等水动力参数变化特征.验证结果显示:水动力模拟结果与实测值吻合较好,模型计算结果有效可靠.模拟结果显示:城陵矶综合枢纽调度运行后,能够有效抬升全湖水位0.78~1.06 m,增加湖泊面积5.96%~10.84%,增加湖容31.18%~39.69%.枢纽工程对缓解洞庭湖秋季旱情、春季旱情作用明显,能够在一定程度上解决洞庭湖枯水期提前、枯水期延长、枯季水位偏低等问题.随着水位的抬升,湖体流速有不同程度的减小,退水期、枯水期平均流速由0.30 m·s-1和0.23 m·s-1降至0.28m·s-1和0.19 m·s-1,分别降低了6.67%、17.39%.城陵矶综合枢纽运行后,水流速度减缓、水体滞留时间延长,将加大湖体富营养化风险.

Impact simulation of the Chenglingji hydraulic project on hydrodynamics of Dongting Lake

In recent years, seasonal hydrological drought in Dongting lake became serious due to lower rainfall and the impoundment of Three Gorges Project etc. In order to mitigate the hydrological drought, Hunan and Hubei governments put forward the construction of Chenglingji hydraulic project (CHP). However, CHP would alter the hydrodynamics and consequently change the water ecological environment. Therefore, a two-dimensional model for Dongting lake based on the MIKE 21 software was constructed to predict the possible influence of CHP on the characteristics of water level and velocity of Dongting lake. The simulation results show that the CHP''s operation would effectively uplift the whole water level of 0.78~1.06 m, increase the lake area of 5.96%~10.84%, and raise the lake volume about 31.18%~39.69%. The verification results show that the simulation values were coincide with the measured values, which proved that the model were efficient and reliable. CHP could mitigate prominently seasonal hydrological drought (autumn, spring drought) of Dongting Lake and solve the problems to some extent, such as earlier and longer dry season and lower water level. However, the uplifting of the water level resulted in lower water velocity. The velocity would decrease from 0.3 m·s^-1 to 0.28 m·s^-1 at water-falling stage and from 0.23 m·s^-1 to 0.19 m·s^-1 at drought period. The change would extend the water retention time and then increase the risk of eutrophication in the lake.