Department of Earth Science |Northeastern Illinois University

ESCI 337
Fall, 2005

Daily Objectives #24 (November 28, 2005)                                        Dr. Sanders

At the beginning of class, please hand in your cross sections and topo map with the lines of x-sec drawn on it. 

By the end of today's class, you should be able to do the following:

v Conceptual Models

        * List and describe the three components of a conceptual model: hydrostratigraphic units, boundaries, and stresses.
        * Based on the geologic cross sections constructed by all of your group members, make a conceptual model for your study area.
        * As a group, write a description of your conceptual model to put in your final paper.

v  Ground Water Modeling: Theory

   r Explain the difference between an analytical model and a numerical model
       r Explain the theoretical basis of a numerical model of ground water flow. 
       r Explain the purpose and use of a grid in ground water modeling.
       r Give the formulas for calculating hydraulic head within a grid cell in ground water modeling, and show that you can use them in hand calculations.
       r Explain what an iteration is, and how it is used in modeling along with initial values (initial heads) and the method of successive approximation.
       r Explain what a residual is, what a convergence criterion (also called a tolerance) is, and how they are used in modeling.
       r Describe the steps in constructing a model, as given on pages 526-527 of the Fetter textbook.

v  Ground Water Modeling: Practice

On the attached file is a 5 x 5 grid of dots that symbolize a plan view of wells tapping a confined aquifer.  Begin with the upper bounday (closed circles) having a specified constant head of 40 m, and the big dark circle in column one, row three having a specified constant head of 0 m.  Calculate the head values for the other wells.  Do this by using successive approximations (iterations).  Record the results of your calculations on the page, showing the head in each well next to each dot.  Note: you will need to assign an initial head to the open circles for your first iteration.  You could choose anything, but let's all choose the same thing for now: 20 m. 

When you are satisfied with your results, calculate the residual (or error, as GGW calls it) for each step.  This means the difference between  head values calculated at each successive step.  How small do they get?  How small do you want them to get? (i.e. what's the convergence criterion?)  How do you know when to stop?

v Now, transfer what you have learned from these hand calculations into a computer model.  Using Graphic Groundwater (see next step), create a model for the area you just worked on.  Use a uniform 5 x 5 grid.  Make sure your model is in keeping with the conceptual model described in class.  See this file for more detailed information.

v Ground Water Modeling Software: Download and install a copy of Graphic Groundwater (GGW).  First, download Version 3.47 and install it.  Then download Version 3.52; it is simply an update and not the full version, so you'll need to install 3.47 before 3.52 will work.  Open up and run the sample model (see the links below).

Please note: Some of the GGW links work only in Internet Explorer, and not in Netscape.  The opposite may be true for some of the ESCI 337 course pages, which I compose in Netscape.  As a general rule, if you are having trouble with a link, try opening the page in a different browser.

v You may wish to examine the files below as a sample of a GGW model.  To get each file, double click on the link and select "Save File", then save each file in a place where you can find it again.  If that doesn't work, then just right click on the link on this page and select "Save Link Target As".  Then save it to a place where you can find it again.

(1) GGW Model for the Holiday Hills Community (file extension ".ggw")     

(2) Map Image for Holiday Hills (file extension ".bmp")

(3) Grid for this model (extension .xls) (you don't need this one to run the model, but you might want to look at it for your own information)

Department of Earth Science | Northeastern Illinois University
© 2005 Laura L. Sanders.  Last updated November 28, 2005.