CE En 547 - Midterm Exam #1 KEY

Fall Semester 2017

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Essay Questions

Click here to access the Equation Sheet.

20. (4 pts) (head-darcy) What is the difference between porosity and effective porosity? Describe the conceptual difference, not just the numerical difference.

21. (head-darcy) Water flows from a lake to an underlying aquifer through three layers of soil as
shown below.

a) (4 pts) How much water (in ft^3) is lost through the bottom of the lake per square foot of the lake per year?

b) (3 pts) What percentage of the total head loss is dissipated in the clay layer?

22. (modflow) Suppose that the lake of the previous problem was to be represented using the
general head package. If a cell covering a portion of the lake had dimensions of 200 ft X 250 ft, what value would you use for the following two general head parameters assigned to the cell?
a) (1.5 pts) Head
b) (2.5 pts) Conductance

23. (4 pts) (gw-concepts) Describe two different uses of ground water models (based on the three primary uses we discussed in class).

24. (4 pts) (gw-concepts) There is an old saying: All models are wrong, but some are useful. What do you think this means?

25. (4 pts) (head-darcy) For a particular site, the average seepage velocity was determined to be 1.4 m/d. The effective porosity at the site was 0.1. The average gross cross-sectional area of flow was determined be 120 m^2. How much water [m^3] would flow through the system in 10 day's time?