Objectives 18

Department of Earth Science |Northeastern Illinois University

PRINCIPLES OF HYDROGEOLOGY
ESCI 337
Fall, 2007

Daily Objectives #18 (October 30, 2007) Dr. Sanders

See the instructions for Homework #5 at the bottom of this page!

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

v Ground Water Modeling: Conceptual Model

List and describe the components of a conceptual model, the first part of constructing a ground water model.
For a specific study site, identify and characterize each component of a conceptual model.

v Ground Water Modeling: Numerical Model

Explain the difference between a conceptual model and a numerical model.
Explain the purpose of a numerical model grid.
Explain how Darcy's law is used in a numerical model

v Ground Water Modeling: Practice

Describe the steps in constructing a model, as given on pages 526-527 of the Fetter textbook.
Download and install the modeling program Graphic Groundwater, authored by Dr. Steven Esling at SUI/Carbondale.
Run Graphic Groundwater for a given study site.

Today's Agenda:

v Ground Water Modeling: Conceptual Models

Describe the components of a conceptual model, the first part of constructing a ground water model:

Hydrostratigraphy
Boundaries (identify location and type)
Stresses (this usually refers to pumping wells and recharge from infiltration)
Initial conditions (water levels)

For our study area, describe each of the above components of the conceptual model.

v Ground Water Modeling: Numerical Models

As an individual

Take a cube of "aquifer" and label it Top, Bottom, Left, Right, Front, Back. Imagine water is flowing from left to right through the cube. Write a formula that quantifies the discharge through the cube. What would you have to know to calculate the discharge?
Imagine water is flowing from front to back through the cube. Write a formula to quantify discharge through the cube. What is different this time? What is the same? What would you have to know to calculate the discharge?
Imagine water is flowing from top to bottom through the cube. Write a formulat to quantify discharge through the cube. What is different? What is the same? What would you have to know to calculate the discharge?
Imagine water is flowing diagonally from the top left front corner to the back right bottom corner. Write a formula to quantify discharge through the cube. What is different? What is the same? What would you have to know to calculate the discharge?

Working with others

Cooperating with another person, line up three cubes in a row. Imagine water is flowing from left to right through the line of three cubes. If you are given the hydraulic head values at the points in the exact center of each of the three cubes, how would you calculate discharge through the center cube? (Note: This is the basis of a "block-centered grid"--as opposed to a "mesh-centered grid", where you would be given the hydraulic head value at the left and right faces of the cubes.)

Now line up nine cubes in a three-by-three layer. Imagine water is flowing through the nine cubes at some angle going roughly from left to right but not perfectly parallel with the cube faces. If you are given the hydraulic head values at the points in the exact center of the eight cubes surrounding the center one (but not the center one itself), how could you figure out the hydraulic head value within the center cube?

What if you knew the hydraulic head in only three of the cubes--how could you calculate the value in the center one?

Look at the example of 27 cubes stacked together. If we know the hydraulic head within every single cube except the center one, how can we calculate head in the center one?

Slice the stack of 27 cubes vertically into left, center, and right. Imagine we know the hydraulic head in the left vertical slice of cubes and the right slice, and we know it is constant with time. How does this help us with calculating the hydraulic head in the center slice?

Imagine there is a change or stress to the system (for example, a well starts pumping, it rains and recharges the aquifer, there's a flood, evaporation takes water out, recharge comes into the aquifer from a far-away outcrop exposure, an injection well is used to pump water into the aquifer). How does this affect hydraulic head in the cubes?

What if we know the hydraulic head in only a few of the cubes? Can we still calculate the value in the center one?

Explain how the concept of boundaries applies to your calculations.

Explain the concept of using a grid in a numerical model.

For further thought

Explain how the concept of anisotropy applies to your calculations.
Explain how the concept of inhomogeneity applies to your calculations.

v Ground Water Modeling: Practice

Ground Water Modeling Software: Download and install a copy of Dr. Steven Esling's program, 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.

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". Remember where you save it to, so 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)

Homework for Thursday, November 1:

1) Write a 1-2 paragraph description of the geology of the study area. (Refer to the cross section.)
2) Write a 2-3 paragraph description of the conceptual model, including at this point, the hydrostratigraphy and the boundaries to the flow system (we will add the other components next time).

Want some serious fun? Get a sneak preview of the instructions for making a grid and constructing your own model. Download and read these two documents: First Steps and Building Your Model A graphic image of our study area is posted here!

Department of Earth Science | Northeastern Illinois University