The grid in MODFLOW uses block-centered nodes; the locations at which calculations are made are at the centers of blocks. Unlike PHAST, in MODFLOW the layers are not required to be flat. Instead, the top and bottom of each cell can be different (fig. 2). In MODFLOW the grid is numbered with 1, 1, 1 in the furthest upper left corner (fig. 3).
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Figure 2. Side view of a MODFLOW grid showing non-uniform layer boundaries. |
In ModelMuse, groups of layers can be defined in the MODFLOW Layer Groups dialog box. Each group of layers shares a variety of common properties. If the model is to be a quasi-3-D model, some layer groups can be designated as nonsimulated in the MODFLOW Layer Groups dialog box. Data sets (described in the next section) are used to define the bottom of each layer group. An additional data set is used to define the top of the model.