CE En 547 - Final Exam KEY

Fall Semester 2018

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Short Answer

Click here to access the Equation Sheet.

18. (1 pt) (modflow) With the Drain package, if the head is below the bottom elevation of the drain, the flow rate is .

19. (head-darcy) A small irrigation reservoir is built on a relatively permeable deposit of sandy soil. To improve the holding capacity of the reservoir, a compacted clay liner is constructed on the bottom of the reservoir. The stage in the reservoir averages about 1020.5 m. The average depth of the reservoir is about 5 m. The clay liner has a thickness of 1 m. The area of the reservoir is about 8000 m^2. After accounting for inflow and outflow and evaporation, it appears that about 1000 m^3 of water is lost from the reservoir each month (every 30 days) due to leakage through the liner. Assume that there is free gravity drainage into the underlying soil beneath the liner (head = elevation at the bottom of the liner).

a. (1 pt) What is the volumetric flow rate representing the drainage through the liner [m^3/d]?



b. (1 pt) What is the hydraulic gradient through the liner?



c. (1 pt) What is the vertical hydraulic conductivity of the clay liner [cm/s]?

20. (head-darcy) Assume that you computed k = 7.4e-5 cm/s for the previous problem. Suppose the owners decide to drain the reservoir and put down a thin pre-fabricated bentonite liner on top of the compacted clay liner to improve the performance of the liner. The bentonite liner is 1.0 cm thick when fully hydrated and the hydraulic conductivity of the bentonite is 1.0e-8 cm/s.

a. (1.5 pts) What is the equivalent hydraulic conductivity of the new liner [cm/s]?



b. (1.5 pts) How much water would be lost per month with the new liner [m^3]?

.

(note: Don't worry about how this number compares to the 1000 m^3 value mentioned above. The K value for this problem is not the correct value).

21. (head-darcy) A piezometer is placed in the ground at a site. The screen on the piezometer is at a depth of 23.75 m. The elevation of the ground surface where the piezometer is located is 1024.0 m above mean sea level. The pore pressure measured by the piezometer is 109.9 KN/m^2. Assume that sea level is the datum. At the location of the piezometer screen;

a) (1 pt) What is the elevation head?



b) (1 pt) What is the pressure head?



c) (1 pt) What is the total head?

22. (3 pts) (goveq) List the three primary assumptions we made when deriving the governing differential equation describing groundwater flow.

23. (1.5 pts) (stochastic) With the latin hypercube sampling technique, the objective is to ensure that the parameter space is explored more fully and it results in a confidence of results with model runs.

24. (1.5 pts) (sustain) The notion that one can determine the perennial yield of an aquifer simply by looking at a flow budget is called .