Geology 724
Spring 2001
Quiz (50 points)
Name________________________________________________
1. Indicate whether the statement is true (T) or false (F).
(15 points)
a) In the Island Recharge Problem, the calibration is more sensitive to hydraulic conductivity
(K) than to recharge (R).
b) As a general rule there should be a minimum of five time steps in each stress period.
c) Suppose we design a two-dimensional profile model of an unconfined aquifer using
MODFLOW in “layer orientation” (i.e., using multiple rows and columns but only one layer).
In this simulation, the value for the parameter “laycon” should be set to represent a confined
aquifer.
d) A steady state model solved using the LaPlace Equation with all specified head boundary
conditions is insensitive to changes in hydraulic conductivity.
e) Land surface elevation is never input to MODFLOW unless the ET (evapotranspiration)
package is used.
2. Briefly answer the following questions.
(30 points)
a) What is the purpose of a sensitivity analysis?
b) Define sensitivity coefficient.
c) Define conductance as a function of leakance.
d) UCODE is a parameter estimation code that solves the inverse problem. Explain what
this means as applied to groundwater flow modeling. That is, what does this code do
when applied to a groundwater flow problem?
e) Describe three ways in which a finite element model differs from a finite difference
model.
f) GFLOW is an analytic element code. Briefly explain how the AE method differs from
the method of finite differences.
g) Describe how each of the following is used in a particle tracking code.
1. Darcy’s law.
2. Interpolation scheme
3. Tracking scheme (e.g., Runge Kutta method)
h) Name three techniques that can be used to define the boundary conditions of a finite
difference model when physical boundaries are located far from the area of interest.
3. Consider the 6 nodes shown below. Suppose these nodes are the 6 nodes in the upper left
hand corner of a two-dimensional horizontal finite difference grid of a confined aquifer. The
nodes in the top row are specified head cells and the nodes in the bottom row are active cells
in a steady-state simulation. The numbers in each cell are the head values. Suppose we wish
to switch from the specified head boundary conditions used in the steady-state model to
specified flux boundary conditions in preparation for a transient simulation involving a
pumping well located somewhere in the problem domain. Calculate the values of the
volumetric flux (m3/day) that you would assign to boundary cell A. Be sure to indicate the
sign of the flux, where (+) indicates inflow to the model and (–) indicates withdrawal of water
from the model. Assume that the aquifer is isotropic and transmissivity is 300 m2/day; the
nodes are equally spaced such that x =y = 100 m.
(5 points)
Cell A
12
9
8
11
10
9