水位波动对洞庭湖洲滩潜流带水热传输影响

Influence of Water Level Fluctuation on Water and Heat Transfer in the Island Riparian Zone of Dongting Lake

选取三峡大坝下游洞庭湖岳阳段某一洲滩作为试验场地,实时监测洲滩剖面的河流水位、水温以及洲滩地下水水位、土壤含水率变化与温度分布。通过分析洲滩内部热通量、潜流交换速率,定量描述洲滩潜流带水热传输特征,刻画洲滩潜流带与地下水位、水温和气温之间的响应关系。结果表明:洲滩内部热通量与气温具有极强的正相关性,可以用日均气温推算洲滩热通量变化;以监测井T1不同深处土壤含水率反求的潜流交换速率变化范围为-5.34×10^(-6)~6.78×10^(-5)m/s;冬季,地下水位变化会延缓洲滩内部热通量由负值转换为正值的时间;洲滩在河水和洲滩潜流带地下水互补过程中损失热量,地下水位越低,波动越频繁,损失热量越大,且主要集中在地面以下0.5~0.7 m。研究揭示了大坝运行对下游洲滩潜流带的影响规律,为河流潜流带生态影响评估提供参考。

A set of field experiments have been made in the island riparian zone of Yueyang in the Dongting Lake downstream of the Three Gorges Dam,for the real-time monitoring water level and temperature of the river,as well as the groundwater level,soil moisture content and temperature distribution of the island profile.Based on the analysis of the heat flux and the hyporheic exchange rate in the island riparian zone to describe the characteristics of the water and heat transfer quantitatively and portray the response relationship between the groundwater level,water temperature and air temperature.The results show that:there is a strong positive correlation between internal heat flux and air temperature,daily average temperature can be used to calculate the heat flux.The change range of hyporheic exchange rate obtained by the soil moisture content at different depths of monitoring well T1 is-5.34×10^(-6)-6.78×10^(-5)m/s.In winter,the change of groundwater level will delay the time when the heat flux changes from negative to positive.The island loses heat during the complementation process between the river and the groundwater of the island riparian zone,the lower the groundwater level,the more frequent the fluctuations and the greater the heat loss,the heat loss mainly concentrated at 0.5-0.7 m below the ground.The results reveal the impacts of dam operation on the downstream island riparian zone hyporheic zone,which will provide the reference for the further ecological impact assessment of the hyporheic zone.