Department of Earth Science |Northeastern Illinois University

ESCI 337
Fall, 2007

Daily Objectives #20 (November 6, 2007)                                        Dr. Sanders

By the end of today's class, you should be able to do the following:
v Ground Water Modeling: Practice
  • Use Graphic Groundwater to create a model or a given study site.  Review
  • Assign reasonable values to the variables in the model, and support your choice for each variable.  Review
  • Explain what the results of your model are (i.e. tell what the direction of flow is, and how pumping affects the flow system).
  • Explain/defend the results of your model, telling if/why it is a reasonable representation of the flow system.
  • Explore what happens to the modeled flow systems when you change values for variables.
  • Evaluate and describe the degree of uncertainty in your model.
  • Do a "sensitivity analysis" for your model.

Today's Agenda:

v Ground Water Modeling: Practice

(Continued from last time) How do we come up with "hard numbers" for each variable in a ground water model?  Find reasonable values or ranges of values for these variables:
What do the results of the model tell us?  What is the direction of flow?  How does water enter the flow system, which way does it move, and how does it exit the flow system?

At a minimum, your model should be running before you leave today!  If you already have a running model, spend your time today working on evaluating it (below).  Take good notes on your work!  You will need them when you write up your results.

v Ground Water Modeling: Evaluating the Model

How good is your model?  First, apply the "Is this reasonable?" test.  Does it show water flowing in what appears to be a reasonable direction?  Are there good reasons for the gradients to be as indicated on the map?  Does the five-year recharge area look reasonable?

Second, try changing some variables and see what happens. 
Consider how good your estimates are.  How reliable is your estimate of, for example, hydraulic conductivity?  Could the actual value reasonably be higher?  Lower?  By how much?  Change the values and re-run the model; see how the results differ.  Here are some suggested approaches  Finally, do a "sensitivity analysis": Now that you know the effect of changing each variable, rate the effect as "strong", "moderate", or "minimal". 

Department of Earth Science | Northeastern Illinois University

© 2007 Laura L. Sanders.  Last updated November 6, 2007.