Abstract:
The Variably Saturated Flow (VSF) Process enables MODFLOW (MF2K v15) to simulate three dimensional variably saturated flow in porous media. The VSF Process includes five packages unique to unsaturated flow; the Richards' Equation Flow (REF1) Package, the Seepage Face (SPF1) Package, the Surface Ponding (PND1) Package, the Surface Evaporation (SEV1) Package, and the Root Zone Evapotranspiration
... (RZE1) Package. Additionally a new Adaptive Time-Stepping (ATS1) Package is introduced for use by both the Ground-Water Flow (GWF) Process and VSF. Processes may be active or inactive, depending on simulation objectives; however, not all processes are compatible. For example, the Observation, Sensitivity and Parameter Estimation Processes are not compatible with VSF. The VSF computer code was tested against two published one-dimensional simulations, two published two-dimensional simulations and against an existing two-dimensional model (VS2DT).
[Summary provided by the USGS.] 
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