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Evaluation of MODFLOW-LGR in Connection with a Synthetic Regional-Scale Model

机译：综合区域尺度模型对MODFLOW-LGR的评估

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This work studies costs and benefits of utilizing local-grid refinement (LGR) as implemented in MODFLOW-LGR to simulate groundwater flow in a buried tunnel valley interacting with a regional aquifer. Two alternative LGR methods were used: the shared-node (SN) method and the ghost-node (GN) method. To conserve flows the SN method requires correction of sources and sinks in cells at the refined/coarse-grid interface. We found that the optimal correction method is case dependent and difficult to identify in practice. However, the results showed little difference and suggest that identifying the optimal method was of minor importance in our case. The GN method does not require corrections at the models' interface, and it uses a simpler head interpolation scheme than the SN method. The simpler scheme is faster but less accurate so that more iterations may be necessary. However, the GN method solved our flow problem more efficiently than the SN method. The MODFLOW-LGR results were compared with the results obtained using a globally coarse (GC) grid. The LGR simulations required one to two orders of magnitude longer run times than the GC model. However, the improvements of the numerical resolution around the buried valley substantially increased the accuracy of simulated heads and flows compared with the GC simulation. Accuracy further increased locally around the valley flanks when improving the geological resolution using the refined grid. Finally, comparing MODFLOW-LGR simulation with a globally refined (GR) grid showed that the refinement proportion of the model should not exceed 10% to 15% in order to secure method efficiency.
机译：这项工作研究了利用MODFLOW-LGR中实施的局部网格细化（LGR）来模拟与区域含水层相互作用的地下隧道山谷中的地下水流的成本和收益。使用了两种替代的LGR方法：共享节点（SN）方法和幻影节点（GN）方法。为了节省流量，SN方法要求校正精/粗网格界面处单元格中的源和汇。我们发现最佳校正方法取决于大小写，并且在实践中很难识别。但是，结果显示出很小的差异，表明在我们的案例中，确定最佳方法的重要性很小。 GN方法不需要在模型的界面处进行校正，并且使用的插值方案比SN方法更简单。更简单的方案速度更快，但准确性较低，因此可能需要进行更多的迭代。但是，GN方法比SN方法更有效地解决了流量问题。将MODFLOW-LGR结果与使用全局粗（GC）网格获得的结果进行比较。 LGR仿真需要比GC模型长一到两个数量级的运行时间。但是，与GC模拟相比，埋谷周围数值分辨率的提高大大提高了模拟水头和水流的精度。使用精制网格提高地质分辨率时，山谷两侧的局部精度进一步提高。最后，将MODFLOW-LGR模拟与全局精炼（GR）网格进行比较表明，为了确保方法效率，模型的精炼比例不应超过10％至15％。

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  • 来源
    《Ground water》 |2012年第1期|p.118-132|共15页
  • 作者

    Troels N. Vilhelmsen; Steen Christensen; Steffen W. Mehl;

  • 作者单位

    Department of Earth Sciences, University of Aarhus, Hoegh-Guldbergs Gade 2, 8000 Aarhus C, Denmark;

    Department of Earth Sciences, University of Aarhus, Heegh- Guldbergs Gade 2, 8000 Aarhus C, Denmark;

    Department of Civil Engineering, California State University, Chico, CA 95929,U.S. Geological Survey, Boulder, CO 80303;

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