CE 473/573 Groundwater
Fall 2008
Homework 2
Due Wednesday September 17
Again, this homework assignment is to be completed in your homework group. Make sure
your group also submits the expectations sheet.
*10. To determine the hydraulic conductivity of a clay, you conduct a test with a falling
head permeameter. The soil sample is 10 cm long, and its cross sectional area is
100 cm2 . The cross sectional area of the tube in which the water falls is 4 cm2 . Determine the hydraulic conductivity from the measurements listed below.
Time (days)
0
1
2
5
10
15
20
25
Head (cm)
5.0
4.6
4.4
3.4
3.1
1.8
1.4
0.9
11. A confined aquifer has length L = 7.5 km, thickness b = 30 m, hydraulic conductivity
K = 3 × 10−5 m/s, and effective porosity n = 30%. The head on the west side of the
aquifer is h0 = 2.5 m, and the head on the east side is hL = 1 m.
a. What is the flow per unit width?
b. Is Darcy’s law valid in this aquifer?
c. How long does it take water to travel from one side of the aquifer to the other?
*12. Test PMWIN and Modflow by solving for flow in the aquifer in problem 10.
a. Run the model and plot the head contours as well as the head as a function of
distance. Explain whether the model produces results that match the analytical
result.
b. Verify that the flow is correct.
c. Double the hydraulic conductivity but keep the same boundary heads. Check the
heads and flows and convince me that the model is working properly.
*13. Construct a Venn diagram for the terms aquifer, aquifuge, aquitard, confining layer,
unconfined aquifer, confined aquifer, artesian aquifer, phreatic aquifer, and perched
aquifer.
14. Do problems 9, 11, and 13 on p. 111 in Fetter’s book. (Answers are in the back.)
*15a. A confined aquifer of area 150 km2 and initial thickness 40 m compacts 0.1 m when
the head is lowered by 10 m. If the porosity after compaction is 20%, compute the
volume of water released from storage. Which is responsible for more of the released
water—the compressibility of the aquifer skeleton or the compressibility of the water?
*b. Suppose the aquifer in part a is unconfined with a specific yield of 15% and other
parameters as in part a. Compare the volume released from storage in the confined
and unconfined aquifers and explain why the difference occurs.