Department
of Earth Science |
Northeastern
Illinois University
PRINCIPLES
OF HYDROGEOLOGY
ESCI
337
Spring,
2004
Daily Objectives #23 (April
13, 2004)
Dr. Sanders
Reminder:
Homework
Assignment #7 is due on Thursday!
By
the end of today's class, you should be able to do the
following:
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 100 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: 50
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?
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 describe in
class. See
this file for more detailed information.
© 2004 Laura L.
Sanders.
Last updated April 13, 2004.