1. Answer either a) OR b) on a separate sheet of paper (20 points)

a) In many groundwater models, rivers that occur in the flow domain are established as constant head cells. In MODFLOW, how would you choose between simply modeling rivers as constant head cells or doing a full-blown implemention of the RIVER package?

b) Say there’s a lake in the area you are interested in modeling. You know that the large changes observed in lake level are controlled almost entirely by changes in the head of the underlying aquifer (streams neither flow in nor out of the lake). How might you go about using MODFLOW to simulate changes in lake level due to stresses on the connected aquifer? (Assume you do not have access to any add-on LAKE packages).
 

2. Give a short answer to each of the three following questions (10 points each)

a)What does the IUNIT array do?
 
 
 

b)Cell-by-cell flow terms can be printed by implementing the OUTPUT CONTROL option and setting the correct flags. What is MODFLOW’s “cell-by-cell flow”, anyway?
 
 
 

c)What’s the difference between a stress period and a time step?
 
 
 
 

3. (50 points) Use the attached MODFLOW input data sets to answer the following questions. (When appropriate, circle the correct italicized response).

a. On the back of the test, sketch the discretized model. In addition to the grid and its dimensions, show no-flow cells, boundary conditions, and boundary cells for the upper layer.

b. What might these boundary conditions represent in nature?
 
 
 

c. Can the lower layer switch from confined to unconfined if cells in the layer above go dry? yes or no What storage value will be used if cells in the upper layer go dry?

                              storage value______________________

d. Are the hydraulic conductivities in the upper and lower layer the same or different?
 

e. Is the model steady-state or transient?
 

f. Does the lower layer have any constant head boundaries? yes or no
 

g. What packages other than BAS, BCF, and SIP are implemented in this model?

    list their extensions:_______________________________________________

h. On output, what head value will be assigned to inactive cells? ____________

i. What time units are used? _____________

j. What length units are used? _____________