CE 473/573 Groundwater
Fall 2009
Homework 3
Due Friday September 25
*14. A confined aquifer has a heterogeneous distribution of hydraulic conductivity.
a. Compute the effective hydraulic conductivity in the aquifer below.
b. Show that your result satisfies at least two special cases.
c. Which soil controls the effective hydraulic conductivity of the aquifer—the low
conductivity soil or the high conductivity soil? Explain your answer.
L1
L2
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Flow
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K2
K1
b
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h = hL
h = h0
*15. Suppose you are asked to set up a groundwater model for a confined aquifer consisting
of silty soils. Heads are measured at three observation wells, as shown below. To calibrate your model, you must choose the values and spatial distribution of the hydraulic
conductivity.
a. Choose a field of hydraulic conductivity to reproduce the measured heads.
b. Compute the flow per unit width in the aquifer if the thickness is 5 m.
c. Discuss any challenges or uncertainty you may have encountered in this problem.
10.00 m
9.00 m
9.17 m
500 m
500 m
*16. Fig. 3.32 of Fetter’s book shows ground water elevations in wells screened in an unconfined aquifer in Milwaukee, WI (See analysis problem B, p. 109). Further information
is listed under lecture 11 on the CE 473/573 website.
a. Are the soils in the study area homogeneous? Are they isotropic? Cite evidence.
b. Estimate the flow across (i.e., normal to) the line between R21E and R22E in the
row T8N. Assume the line is in the till. Recall that the aquifer is unconfined, so
that the flow thickness is not constant. Also, remember to subtract the elevation
of the bottom of the aquifer when computing the thickness.
c. Does water flow into or out of the lake in T8N, R22E? What about in the other
areas of R22E?
17. Now that we have discussed aquifer properties, Darcy’s law, and conservation of mass,
redo problem 1b.
18. Suppose for the steady 1D flow in a confined aquifer the head and flow per unit width
at x = 0 are known (i.e., h = h0 and Q = Q0 at x = 0). Compute the hydraulic head
as a function of x.
*19. For the same flow in a confined aquifer, which has a larger gradient—coarse sand or
silt? For the same gradient in a confined aquifer, which has a larger flow—coarse sand
or silt?