2.6.2.3.4 Model code and solver

The model was run using the MODFLOW-USG, the unstructured grid version of MODFLOW (Panday et al., 2013). Many local and regional groundwater models of CSG and coal mining in the Namoi subregion use versions of MODFLOW (see Section 2.6.2.2). MODFLOW-USG is an open-source code and meets the transparency requirements of BA. The code was assessed against the following criteria:

open source and well tested – MODFLOW-USG is open source and has been used in many groundwater models
able to run in batch-mode on high-performance computing clusters to complete the uncertainty analysis – multiple single-core MODFLOW-USG jobs may be submitted to compute clusters
able to represent both fine spatial details horizontally around mines, as well as a large regional area – MODFLOW-USG can use an unstructured grid to capture spatial detail in plan (x, y) view
able to enhance hydraulic conductivity around longwall mines – changes in the hydraulic properties above longwall mines caused by subsidence can be simulated in MODFLOW-USG using the Time Varying Materials package
numerically stable so that certain parameter combinations encountered in the uncertainty analysis do not cause the program to crash – user experience with conventional MODFLOW is that sometimes-certain parameter sets cause it to fail. MODFLOW-USG has enhanced features and flexibility in the design of the model grid that helps to achieve better stability.

In conclusion, MODFLOW-USG has the features necessary to build a fit-for-purpose groundwater model of the Namoi subregion.

Last updated:

6 December 2018

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