of Earth Science |Northeastern
Objectives #21 (November 8,
the end of today's class, you
should be able to do the following:
v Ground Water Modeling: Practice
what the results of your model are (i.e. tell what the direction of
flow is, and how pumping affects the flow system). Review
the results of your model, telling if/why it is a reasonable
representation of the flow system. Review
what happens to the modeled flow systems when you change values for
"sensitivity analysis" for your model.
v Ground Water Modeling: Evaluating the Model
last time) 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 to the
five-year recharge area. 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
Finally, do a
"sensitivity analysis": Now that you know the effect of changing each
variable, rate its effect as "strong", "moderate", or
"minimal". You may wish to use the
document attached here as an aid to organizing your results.
elevation of the aquifer: how close to reality do you think
your input data are? what happens if you change them?
elevation of the aquifer: what if these data were
changed? what would the results look like?
conductivity (horizontal): what's a reasonable range of possible
values? How much difference does it make?
hydraulic conductivity: how does it change the results if the
Kh/Kv ratio is 5:1, or 20:1, instead of 10:1?
to the aquifer through infiltration: what if recharge is
- porosity: what difference would it
make if the porosity were 30%? 20%?
head: how does changing your initial heads change the model
pumping from wells: what if two of the wells were shut down for
maintenance, and the third well had to do all the work? What if
the population of the village increases by 10%, and as a result the
rate of pumping increases by the same percentage?
© 2007 Laura L.
Last updated November 8, 2007.