Grid Design

A uniform 50x50x3 (row, column, layer) grid was utilized, including an area slightly larger than the region of well data included in the RSKERC Hays well database (Fig. 13). Each layer in the MODFLOW grid represents a different lithology/facies: Qt (Layer 1), Qal (Layer 2), Kc (Layer 3)where layer boundaries correspond to the contact surfaces developed in the hydrogeologic model. As such, the model results are calculated on a uniform 3-D grid, with along-layer transmissivity adjusted to reflect variations in aquifer thickness (see [McDonald and Harbaugh, 1988, p. 2-31]). This introduces error in the solution, since the faces of each cell are no longer rectangular, as is assumed in the model formulation. The total error arising from this source is typically found to be quite small [McDonald and Harbaugh, 1988]. Cells for layers 1-2 have zero thickness outside of the valley (i.e. on the Kc side of the Kc-Qt contact, Fig. 6). Material properties used in the best-fit steady-state model are summarized in Table 1.

Figure 13: Modflow model grid, Layers 1 (Qt) and 2 (Qal), Hays, KS and vicinity. Boundary conditions are shown by symbols, city water supply pumping wells indicated by labeled squares, river cells by the '+' symbol. Select image to view full-sized version.

Figure 14: Modflow model grid, Layer 3, Hays, KS and vicinity. Select image to view full-sized version.

Table 1: Material properties used in model. Hydraulic conductivity was obtained during calibration, porosity value is identical to that in earlier studies [Kraemer and Burden, 1994].

Property	Layer 1	Layer 2	Layer 3	Units
Hydraulic Conductivity	5.0	60.0	0.2	$\rm\frac{m}{d}$
Porosity	0.2	0.2	0.2
Layer Type	Unconfined	Semi-Confined	Confined