Week 2

Question 1

Aquifer =

Answer 1

Saturated, permeable geological unit that stores groundwater and allows it to flow under normal conditions

Question 2

Aquiclude =

Answer 2

Saturated geological unit incapable of transmitting significant quantities e.g. could have unconnected voids

Question 3

Aquitard =

Answer 3

Less permeable bed in a stratigraphic sequence

• may be significant in regional groundwater balance
• insignificant for local production well

Question 4

Where does groundwater flow?

Answer 4

B/w grains (minute spaces)

Small cracks/fractures in limestones and chalk

Question 5

How much of the water available to the biosphere is groundwater?

Answer 5

97.5%

Question 6

Total porosity =

Answer 6

nt

vol voids/total rock vol

Question 7

Effective porosity =

Answer 7

ne

vol voids accepting water/total rock vol

Question 8

Drainable porosity =

Answer 8

nd

vol voids drained by gravity/total rock vol

Question 9

Kinematic porosity =

Answer 9

nk

vol flowing water/total rock voil

Question 10

Porosities and their relationship to each other (reasons)

Answer 10

nt>ne>nd>nk

• some voids too small to accommodate water molecules
• some water held against gravity by surface tension
• some pores bypassed/not connected to flowing network

Question 11

Darcy’s Law

Answer 11

Q = -KA x /\h/L

Question 12

Darcy flux

Answer 12

q = Q/A

Question 13

Hydraulic head eqn

Answer 13

hydraulic head = pressure head + elevation head

Question 14

Pressure head eqn

Answer 14

pressure head = P/(density x gravity)

Question 15

Fluid potential

Answer 15

Flow from high to low potential regardless of direction in space; for flow through porous media = mechanical energy (“work done” per unit mass of fluid

Question 16

Converting fluid potential to hydraulic head, steps:

Answer 16

Fluid potential = an energy

1. Potential energy (raise elevation)
   w1 = mgz
2. Kinetic energy (accelerate)
   w2 = mu^2/2
3. pressure energy (raised fluid P)
   w3 = mP/density

Take unit m=1

Divide by g

= h

= z + w

Question 17

Work = (equations)

Answer 17

mass x gravity x height

mass x acceleration

pressure/density x mass

(= (force/unit area)/(vol/unit area) x mass)

Question 18

Observation well

Answer 18

Open borehole

Water level = average h over length of open section

Unconfined aquifers water level = level of prevailing water table –> integrated h

Question 19

Piezometer

Answer 19

Device for measure h AT A POINT (or averaged over relatively small depth)

–> More precise point measurement > observation well

Water level in open piezometer well x = water table in unconfined conditions

Question 20

Hydraulic conductivity =

Answer 20

Ease of flow of fluid

K

Question 21

What does Poiseuilles formula calculate?

Answer 21

The flow through an individual hole

Question 22

k =

Answer 22

Intrinsic permeability

= nD^2/32 (messy bit of Darcy/Poiseuilles formula)

Question 23

Method for using Darcy’s/Poiseuilles formula

Answer 23

1. Compare the two equations
2. Get AK = the messy bit
3. Since A=BH, K = messy bit
4. Recall porosity n = vol voids/total vol
   n = vol of cylinder (void)/vol of cub (total vol)
5. Relate K = and n =
6. Separate fluid component and geometric component
7. k = messy bit
   so K = fluid component

Question 24

Hydraulic head =

Answer 24

Elevation head + pressure head

= elevation at surface - depth to water

Question 25

Elevation head =

Answer 25

Elevation at surface - depth of piezometer

Question 26

Pressure head =

Answer 26

Hydraulic head - elevation head

Question 27

If the spacing of the fractures is S, then the formation thickness, H = ?

Answer 27

NS