HW #8 - MODFLOW Conceptual Model, Part 2
Note: You may work in pairs on this assignment.
In this exercise, you will create another MODFLOW simulation using the conceptual model approach using the tools in the GMS Map Module. Before beginning the exercise, right-click and download the following zip archive. Unzip the resulting file to a new empty directory.
Before describing the model, we will read in the TIFF image of the site map.
1) Import and register the background TIFF image
a) Select the File|Open command and read in the file: sitemap.tif.
b) Position the three registration points on the three red squares in the TIFF image and use the coordinates shown on the image for the real world coordinates of the registration points.
We will build a single layer unconfined model. The model consists of three wells in the locations shown on the background image. The boundary with the inlet will be modeled as a specified head boundary with a head equal to 0.0. The creeks will be modeled as drains. The black line represents a no flow boundary corresponding to groundwater divides and parallel flow lines. We will do a steady state simulation.
Perform the following basic steps:
2) Generate a conceptual model.
a) Create a MODFLOW conceptual model object.
b) Create a coverage named “boundary” and create a set of arcs around the boundary of the model area. Use this as a template for all of your other coverages.
c) Copy the boundary coverage to create a MODFLOW coverage containing sources and sinks.
d) Create the wells. Assign the following values:
Well #1: Q = -25,000
Well #2: Q = -100,000
Well #3: Q = -35,000For all three wells, define refine point data and set the cell size = 100, bias = 1.2, max size = 500.
e) Assign the specified head arc and node attributes.
f) Create drain arcs for the streams and assign the attributes. Visually interpolate elevations from the contours. Each contour line equals 100 ft. Use a conductance value of 300.
g) Build a polygon from the arcs.
h) Copy the boundary coverage to create a coverage to be used for recharge. Assign a recharge value of 0.002 to the entire area.
i) Copy the boundary coverage to create a coverage to be used for hydraulic conductivities. Create three hydraulic conductivity polygons as shown below.
j) Create a Grid Frame. Orient the grid frame along the major longitudinal axis of the conceptual model (NW to SE).
3) Create the grid. Use one layer.
4) Initialize the MODFLOW data.
5) Inactivate the cells outside the coverage.
6) Map the conceptual model to the grid.
7) Define the top and bottom elevations:
a) Open the files: tops.txt and bottom.txt. Use the Text Import Wizard to create 2D scatter points from these files.
b) Interpolate from the scatter points to the MODFLOW layers.
c) Interpolate the top elevations to the Starting Heads array.
8) Select the SIP solver (seems to work better than PCG for this model). Increase the maximum number of iterations in the SIP Package dialog.
9) Check your model for errors and then save and run the simulation.
10) You should see a few dry cells on the left side of the model. Go into the SIP package and lower the acceleration parameter to 0.1. Change the maximum number of iterations to at least 500. Save and run the model. Did the dry cells disappear? Why?
Zip up all files associated with your project. Log in to your student account to upload your zip archive. The questions in the last part are for your own enlightenment. You do not need to include the written answers as part of your solution.