of Earth Science |Northeastern
Daily Objectives #24 (November
the beginning of class, please hand in your cross sections and topo map
with the lines of x-sec drawn on it.
the end of today's class, you should be able to do the
* List and describe
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.
Water Modeling: Theory
Explain the difference between an analytical model and a
the theoretical basis of a numerical model of ground water flow.
the purpose and use of a grid
in ground water modeling.
the formulas for calculating hydraulic head within a grid cell in
ground water modeling, and show that you can use them in hand
what an iteration is, and how
it is used in modeling along with initial
values (initial heads)
and the method of successive
what a residual is, what a convergence criterion (also called
a tolerance) is, and how they
are used in modeling.
the steps in constructing a model, as given on pages 526-527 of the
v Ground Water Modeling:
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
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
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
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.
Model for the Holiday Hills Community (file extension ".ggw")
Image for Holiday Hills (file extension ".bmp")
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)
of Earth Science | Northeastern
© 2005 Laura L.
Last updated November 28, 2005.