Running Visual MODFLOW with a two-layer model & topography

Start Visual MODLFOW. Click on File and open a new model.  Call it whatever you like.

In the model parameters window leave the dimensions as 20 x 20 with 0 to 1000 in both the X and Y direction.  Change Layers(k) to 2 and set Zmin = -35 and Zmax = 35.  Change conductivity units to cm/sec.  Hit Create.

Click on Properties and then Conductivity.  Set the conductivity for the upper layer to 0.01 cm/s in the X and Y directions and 0.005 in the Z direction.  Set Specific storativity (Ss) to 0.005, Specific yield (Sy) to 0.20, and the two porosity values to 0.20 and 0.25.

Click on Boundaries and then on Constant Head.  Establish a Constant Head boundary at the top of the drawing by clicking on Assign and then Line.  Using the mouse draw a line across the top row of cells (from left to right), and then click the right mouse button in the top-right square.  Enter the following values: Stop time: 500 days, Start Pt. 25, End Pt. 25.

Establish another Constant Head boundary at the bottom of the drawing by clicking on Assign and then Line.  Using the mouse draw a line across the bottom row of cells (from left to right), and then click the right mouse button in the bottom-right square.  Enter the following values: Stop time: 500 days, Start Pt. 1, End Pt. 1.

Click on Boundaries and then on Rivers.  Establish a River boundary along the left side of the drawing by clicking on Assign and then Line.  Using the mouse draw a line down the left row of cells and then click the right mouse button in the bottom-left square.  Enter the following values: Stop time: 500 days, Start Pt.: Stage 25, River bottom 24, Conductance 100, End Pt.:  Stage 1, River bottom 20, Conductance 100. 

Establish a similar river boundary along the right hand side of the drawing.

Set the Recharge value by clicking on Boundaries then Recharge and setting the values to Stop time 500, Recharge rate 200 mm/y. (Assumes a 20% infiltration rate and a total rainfall of around 1000 mm/y)

To establish a different conductivity for the lower layer click on Properties then Conductivity.  Click the Next button to switch to the lower layer, then click on Assign.  and Window.  Using the mouse draw a window that covers the entire map area.  In the Assign K Property window click New, and then assign Kx and Ky of 0.001 and Kz of 0.0005.

The topography data is stored in the following file: elev-with-creek.txt.  Right click this link and download the file to your computer.  Go and find the file and change it's name from "elev-with-creek.txt" to "elev-with-creek.asc". To input the topography hit F10 then Input.  Click the Import Elevation button and then go and find the “elev-with-creek.asc” file that you just saved.

The model is now ready to run.  Click F10 to go to the main menu, then click on Run and make sure that the Steady State Flow button is selected.  Then click on run again, check the Modflow box and click Translate & Run.

If everything has gone according to plan the model should run properly and you can look at the results by clicking on Output.  Click the Velocities button to see the groundwater flow directions and relative rates.  You can look at the model in plan view (by default) or in cross section by clicking on the View Column or View Row buttons.  After selecting one of these you need to use the mouse to pick a column or row to view.  If you change the vertical exaggeration to something between 5 and 10 you‘ll get a better view of what is happening.  You can scroll through the model row by row or column by column using the Next or Previous buttons.