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assn2_2011 - Assignment 2 2D steady-state models and...

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Assignment 2. 2D steady-state models and introduction to MODFLOW and Groundwater Vistas Presentation of modeling report Jan 12 (Monday). Assignment due. Jan. 14. 60 points. Objectives: Become familiar with the BASIC and BLOCK-CENTERED FLOW packages in MODFLOW, and MODFLOW/Groundwater Vistas input and output. Understand how boundary conditions and convergence criterion affect the results of steady-state simulations. Learn more about modeling from previous modeling reports. In this problem, you’ll be simulating regional flow patterns in a simplified cross- section view (Toth,1963) using MODFLOW and Groundwater Vistas. As you do the assignment, be sure to explore Groundwater Vistas. Try out the various views and methods to input parameters. There are often different ways of doing things, and you will likely be able to find ways that you like better than the way that I suggest. When you installed the software, you also install the Groundwater Vistas manual, GW Vistas tutorials, and MODFLOW (and other program) manuals in the same folder. I don't recommend printing them out (they are hundreds of pages) but start using the manuals as a resource when you run into questions. Keep in mind that in MODFLOW (as in the spreadsheet models), you must use consistent units. For this problem use m and days. Although the Toth problem simulates a cross-section, we will set it up in one MODFLOW “layer”. Start Groundwater Vistas. Select File and New to open the "Initialize Model Grid" dialog box. For this model, specify 10 rows, 21 columns, and uniform x and y spacing of 50 m. Select 1 layers (vertical direction) and set the bottom elevation to 0 and the top elevation to 1 m. Set Kx and Ky to 500 m/day. You'll be running a steady-state simulation, so you do not need to specify storage. The other boxes in the dialog box can also be ignored for now. You’ll use some of these in later assignments. Also, Groundwater Vistas can run other codes as well as MODFLOW, so has many choices that don’t apply to MODFLOW simulations. When you click OK, your grid will appear. The bottom view shows a layer and the top view shows a cross-section. For this part of the assignment, the cross-section won’t look like anything, since you assigned a z dimension of 1 m. Note the numbering scheme for rows and columns starts at 1,1 in the upper left hand corner. Boundary Conditions If you do not enter a boundary condition for the model boundaries, MODFLOW assumes "no flow". So you do not have to do anything to the left, right, and bottom boundaries. To set the top boundary condition, go to the “AE” pull down menu. Choose polyline boundary, and draw a line across the model top row from left to
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right. A dialog box will then open. Enter the head at the beginning (100) and the end
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