河流—地下水系统水量平衡耦合模型分析——以海河流域黎河下游为例

Analysis on water balance of river-groundwater system using coupling models. Case study of lower Lihe River in Haihe basin

为了定量分析海河流域黎河下游水位雍高后周边区域河流—地下水系统水量平衡情况,选取河道水位变幅和河流—地下水间水量交换作为传递变量,以半松散耦合方式构建HEC-RAS与MODFLOW耦合模型,同时借助Picard迭代多次调整系统水量平衡,减小流量残差,实现模型间的参数双向传递,完善模型的双向耦合。利用校验后的耦合模型对黎河下游周边区域河流—地下水系统水量平衡进行研究,结果表明:研究区内水量补给以降雨入渗补给为主,水量排泄以潜水蒸发为主;河道水位雍高使得河流对地下水的补给增大,地下水对河流的排泄减少,但是河流与地下水间的补排关系并未发生改变,与河道水位雍高前相同,即始终由地下水对河流排泄占主导。

This study develops a semi-loose coupling hydrodynamic model integrating the HEC-RAS model and MODFLOW model for quantitative analysis of the water balance in a river-groundwater system, and applies it in a case study of the surrounding area of the lower Lihe River impacted by the mainstream water level. This coupling model adopts two transfer variables： the range of variations in river water level and the volume exchange between river water and groundwater, and reduces flow residual of the system by adjusting its water balance using the Picard iteration, so that bidirectional parameter transmission between the two models and two-way coupling are successfully achieved. Application of the model to calculations of the water balance in the case study reveals that before the water level elevation, most of the water supply in the study area came from rainfall infiltration recharge while the main water discharge was phreatic evaporation. The uplift in water level increased seepage recharge and reduced groundwater discharge, but it produced no impact on the recharge-discharge relation between river and groundwater. Thus, this relation is still dominated by the groundwater discharge to the river, exactly the same as in the previous condition.