MODFLOW 2000 – Developed to Improve Solution Stability and Performance

Under contract to the USDOE, staff at SSP&A modified MODFLOW-2000 (modified-MF2K) to improve handling of cell drying and rewetting in response to a changing water table. This was accomplished by implementing robust numerical techniques including (a) an approximate unsaturated-saturated flow equation, (b) a Newton-Raphson linearization scheme, (c) back-tracking and under-relaxation techniques to provide stability and robust convergence of the flow solution, and (d) an adaptive time-stepping scheme. To achieve rapid convergence of the modified flow equations, an ORTHOMIN numerical solver was also implemented. Tests of the code suggest close agreement between results obtained by the modified-MF2K, MODFLOW-NWT, and MODFLOW-SURFACT (Bedekar et al, 2012).

REFERENCE

Bedekar, V., Niswonger, R.G., Kipp, K., Panday, S. and Tonkin, M. (2012), Approaches to the Simulation of Unconfined Flow and Perched Groundwater Flow in MODFLOW. Groundwater, 50: 187-198. doi: 10.1111/j.1745-6584.2011.00829.x

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