Objectives #24

Department of Earth Science |Northeastern Illinois University

PRINCIPLES OF HYDROGEOLOGY
ESCI 337
Spring, 2004

Daily Objectives #24 (April 15, 2004) Dr. Sanders

Reminder: Homework Assignment #7 is due today!

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

OLD BUSINESS

v Ground Water Modeling: Theory

       r Explain the difference between an analytical model and a numerical model.
   r Explain the purpose and use of a grid in ground water modeling.
   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.

NEW BUSINESS

v Ground Water Modeling: Practice

Review your calculations for the 5 x 5 grid that we worked on in the last class. Calculate the residual for each step. This means the difference between head values calculated at each successive step for a single piezometer. How do they change as you iterate? 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?

Now, transfer what you have learned from these hand calculations into a computer model. Using Graphic Groundwater, 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 step-by-step information on using GGW!

v Ground Water Modeling: The Montgomery Project

Data on the Community Water Supply (CWS) wells that are the focus of our study:

Pumping Rates:    Well #10:    47,421,000 gallons per year
                                   Well #11: 102,587,000 gallons per year

Well Logs

WELL #10	From (ft)	To (ft)	WELL #11	From (ft)	To (ft)
Top soil	0	0.5	Soil	0	9
Brown silty clay	0.5	3.5	Stiff clay with cobbles	9	25
Brownish gravel and many extremely large boulders with fine sand and also blue clay intermixed in spots	3.5	27	Coarse sand and gravel and cobbles	25	35
Brown sandy, silty clay with gravel intermixed and a few boulders	27	39	Coarse sand and small gravel	35	46
Gray fine sand to medium gravel	39	70	Medium sand	46	58
Gray fine sand to coarse gravel	70	82	Coarse sand and gravel	58	59
Green shale with lime	82	87	Bedrock	59

A copy of the bitmap image of the WEST side of the Fox River can be downloaded from this link.
A copy of the bitmap image of the EAST side of the Fox River can be downloaded from this link.
A copy of a generic Excel file to be used in constructing a grid can be downloaded from this link.

A file on a step-by-step approach to building your model appears here.

Department of Earth Science | Northeastern Illinois University