Comparative Assessment of Methods for Coupling Regional and Local Groundwater Flow Models: A Case Study in the Beijing Plain, China

Sida Liu,Mingzhao Xie,Yangxiao Zhou,Xu-Sheng Wang,Michael Mcclain

doi:10.3390/w13162229

Abstract

A coupled regional and local model is required when groundwater flow and solute transport are to be simulated in local areas of interest with a finer grid while regional aquifer boundary and major stresses should be retained with a coarser grid. The coupled model should also maintain interactions between the regional and local flow systems. In the Beijing Plain (China), assessment of managed aquifer recharge (MAR), groundwater pollution caused by rivers, capture zone of well fields, and land subsidence at the cone of depression requires a coupled regional and local model. This study evaluates three methods for coupling regional and local flow models for simulating MAR in the Chaobai River catchment in the Beijing Plain. These methods are the conventional grid refinement (CGR) method, the local grid refinement (LGR) method and the unstructured grid (USG) method. The assessment included the comparison of the complexity of the coupled model construction, the goodness of fit of the computed and observed groundwater heads, the consistency of regional and local groundwater budgets, and the capture zone of a well filed influenced by the MAR site. The results indicated that the CGR method based on MODFLOW-2005 is the easiest to implement the coupled model, capable of reproducing regional and local groundwater heads and budget, and already coupled with density and viscosity dependent model codes for transport simulation. However, the CGR method inherits shortcomings of finite difference grids to create multiple local models with inefficient computing efforts. The USG method based on MODFLOW-USG has the advantage of creating multi-scale models and is flexible to simulate rivers, wells, irregular boundaries, heterogeneities and the MAR site. However, it is more difficult to construct the coupled models with the unstructured grids, therefore, a good graphic user interface is necessary for efficient model construction. The LGR method based on MODFLOW-LGR can be used to create multiple local models in uniform aquifer systems. So far, little effort has been devoted to upgrade the LGR method for complex aquifer structures and develop the coupled transport models.

Highlights

Using a large scale regional model to simulate the local scale groundwater problems can be inaccurate and not cost-beneficial [5] and it is common that the natural hydraulic boundary is located far from to the target local study area so that the extent of the model area becomes much larger than the area of interest [6]
Three coupled models with conventional grid refinement (CGR), local grid refinement (LGR) and unstructured grid (USG) methods were compared with the original regional model [33]
Based on the regional groundwater flow model of the Beijing Plain, a coupled local groundwater flow model with finer grid resolution was constructed with three different refinement methods: the conventional grid refinement (CGR) method based on MODFLOW-2005, the local grid refinement (LGR) method based on MODFLOW-LGR, and the unstructured grid (USG) method based on MODFLOW-USG

Summary

Introduction

Using a large scale regional model to simulate the local scale groundwater problems can be inaccurate and not cost-beneficial [5] and it is common that the natural hydraulic boundary is located far from to the target local study area so that the extent of the model area becomes much larger than the area of interest [6]. In these situations, using unified global refined grids would be computationally expensive [7]

Methods

Results

Discussion

Conclusion