基于嵌套模型的地下水侧向径流边界刻画方法研究——以湖北碾盘山冲积平原地下水数值模拟为例

侧向径流边界的刻画方法是地下水数值模拟中的关键问题。以湖北碾盘山汉江水利水电枢纽工程为例,基于有限单元法和嵌套模型的水量转换方法,分别建立包括完整水文地质单元的区域模型和仅包含汉水Ⅰ级阶地的平原区模型;通过区域模型的分区水均衡运算,计算平原区侧向径流边界的径流量,并以区域模型水均衡为框架,分别采用二类流量边界和一类水头边界刻画侧向径流边界,建立了平原区模型;深入分析区域模型和平原区模型间参数和水量的转换关系,并对比了两类边界条件刻画方法的优缺点和适用条件。结果表明:采用嵌套模型能够得到较为准确的地下水侧向径流量;在平原区模型中采用二类流量边界刻画侧向径流边界有利于提高平原区模型的精度和稳定性;边界条件除具有双重含义外还具有双重特征,在模型建立过程中应充分认识边界条件的位置特征和数量特征,并合理概化。

Study on Characterization Methods of Groundwater Lateral Flow Boundary Condition Based on the Nested Model- A Case Study of Groundwater Numerical Simulation of Nianpanshan Alluvial Plain in Hubei Province

Lateral flow boundary condition is a key issue in numerical simulation of ground water.Taking Nianpans-han hydropower proj ect in Hubei as an example,based on the finite element method and the water transformation of the nested model,this paper sets up a regional model which contains a complete hydrogeological unit and a plain terrain model which only covers theⅠlevel terrain of Han River.Through water balance calculation in different sec-tions of the regional model,the paper confirms the flux of the lateral flow boundary.Then,in the regime of the re-gional water balance,the paper establishes the plain terrain model respectively with the lateral flow boundary depic-ted by the Dirichlet boundary condition and the Neumann boundary condition.Next,the paper analyzes the relation-ship between the two models both in model parameters and water transformation relations,and compares the pros and cons and applicable conditions between the two kinds of boundary conditions in depicting lateral flow bounda-ry.The result shows that accurate lateral groundwater runoff can be calculated by using the nested model,and using Neumann boundary condition depicting lateral flow boundary is helpful to improve accuracy and stability of the plain terrain model.It is concluded that the boundary condition has dual-characteristics along with the dual-mean-ing.In the process of building models,the position characteristics (water level)and the quantity characteristics (water volume)should be fully recognized.