Part I: Multiple Choice (10 pts; 2 pts. each). Which of the following boundary c

Question

Part I: Multiple Choice (10 pts; 2 pts. each). Which of the following boundary conditions is appropriate for a large lake with a good connection to the aquifer 1. a. No-flow b. Constant head c. Specified flux d. (b) or (c). 2. The mass balance calculation in a finite difference model is a measure of the: a. b. c. d. goodness of fit between the modeled and observed heads mathematical accuracy of the solution difference between recharge and pumping appropriateness of the conceptual model 3. The Cooper-Jacob approximation is generally valid for: a. early time b. late time c. observations close to pumping well d. observations far from pumping well e. partially penetrating wells f. (a) and (d) g (b) and (c) 4. For a given specific discharge, solutes in groundwater move faster in an aquifer with: a. b. c. d. higher porosity lower porosity higher hydraulic conductivity lower hydraulic conductivity 5. The amount that a plume spreads as it moves downgradient is a function of: a. seepage velocity b. dispersivity c. d. time of travel all of the above

Explanation / Answer

1. Answer - d.

The boundary condition appropriate for a large lake with a good connection to the aquifer is constant head or specified flux.

Constant head is defined as the head is constant across the boundary means equal amount of recharge and discharge whereas specified flux is recharge or discharge across boundary. As the lake is Lage, so it seems constant head over long time and space, but if we observe at a smaller unit, then there must be a change in head.

2. The mass balance calculation in a finite difference model is a measure of the difference between recharge and pumping.

The mass balance calculation is also known as water balance equation which states the water storage condition in terms of recharge and discharge. If the condition is steady state, there recharge equals the discharge. If not, then the calculation is done by the difference in input and output.

3. Answer - g.

The cooper-Jacob approximation is generally valid for late time and observation close to pumping well.

The above method is applied only for confined aquifer and it is derived from This Theis method. In the Cooper- Jacob method, the drawdown due to pumping is calculated near the pumping well. This method is only valid for fully penetrating well and for homogenous, isotropic confined aquifer.

4. For a given specific discharge, solutes in groundwater move faster in an aquifer with higher hydraulic conductivity.

Darcy's law states,

Q = k A dh/dl

Where, Q = discharge

k = hydraulic conductivity

A = cross sectional area

dh/dl = hydraulic gradient

Now, Q/A = k A dh/dl = q = specific discharge

Therefore the specific discharge is proportional to hydraulic conductivity.

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