User's guide of Proceessing Modflow 5.0

216 Processing Modflow
< To define the aquifer type
1. Select Grid < Layer Type …
2. In the Layer Options dialog box, click on Type and select Unconfined, it is ok to browse
through the rest of this dialog box, but leave all the values as the default ones.
3. Click OK to leave the Layer Options dialog box.
Flow boundaries
MODFLOW uses an array called the IBOUND array to determine if a particular cell is active,
inactive (no flow) or a fixed-head cell. Cells values within IBOUND are as follows:
active = 1 (or other positive integers)
inactive = 0
fixed-head = -1 (or other negative integers)
These values are assigned to cells as required in the Data Editor. By default and convention
the area outside the model domain is deemed to be a “No Flow Zone” and as such it is not
necessary to set this area to inactive.
< To specify the IBOUND data
1. Select Grid < Boundary Condition < IBOUND (Modflow)
2. Ensure the cell selected is [1,1,1] and click the right mouse button to open the Cell Value
dialog box. Since this is going to be a fixed-head boundary enter -1, and click OK to exit
the dialog box. The cell should now have a blue color signifying that it has been set as
fixed-head.
To save doing this for the remaining fixed-head cells it is possible to copy the value (in this
case -1) to any other cell.
3. Click on the Duplication Button , duplication is activated if the relief of the button is
sunk.
4. Simply click the left mouse button in any cell that you want to specify as a fixed-head cell.
If you make a mistake, turn off the Duplication Button and click the right mouse button in
the cell where you have entered the wrong value and replace it with the desired value.
5. Complete specifying the entire North boundary and the portion of the South boundary west
of the mountain as fixed-head cells. We will assign a head value to these cells a little later.
Areas at the model extents are assigned as No Flow by default. However, the mountain area in
the south corner of the domain needs to be explicitly assigned as No Flow (ie. IBOUND=0).
6.1.1 Tutorial 1 - Unconfined Aquifer System with Recharge