Hydrogeology

Question 1

Give examples of geofluids

Answer 1

gas, oil, brine, groundwater

Question 2

What is the difference in pores in the unsaturated and saturated zones?

Answer 2

unsaturated - pores = water and air
saturated - pores = water

Question 3

What is the pressure compared to atm in unsaturated and saturated pores?

Answer 3

p<atm>atm in saturated</atm>

Question 4

where is soil water found?

Answer 4

in the root zone

Question 5

What is a cone of depression?

Answer 5

the shape formed around a groundwater extraction well

Question 6

What are forms of input for the gw system?

Answer 6

recharge usually precipitation. Some of it goes to baseflow for rivers and the rest is extracted

Question 7

What is a major consequence of groundwater extraction?

Answer 7

subsidence

Question 8

Consequences of groundwater abstraction?

Answer 8

increase in irrigation needs
land subsidence in unconsolidated aquifers
increasing costs to lift water from deep aquifers
quality of water deteriorates
risk of saltwater intrusion increases
ecological detereoration

Question 9

How does unsustainable groundwater abstraction impact salinity

Answer 9

the sea level increases with respect to the inland groundwater level and this will cause easier infiltration of brackish water

Question 10

3 forms of recharge

Answer 10

artificial (managed aquifer recharge), natural (rainwater), indirect (aquitard leakage, cross formational flow)

Question 11

pros and cons of surface water

Answer 11

accessible, plentiful, unsteady supply, prone to contamination

Question 12

pros and cons of groundwater

Answer 12

steady, good quality, inaccessible, difficult ot find

Question 13

aquifer

Answer 13

subsurface formation of a porous medium that contains and transmits significant amounts of groundwater

Question 14

difference between aquifer and reservoir

Answer 14

reservoir is the word for hydrocarbons and aquifer for groundwater

Question 15

aquitard

Answer 15

subsurface formation that can store water and has a low transmission capacity. It retards but does not prevent the flow of water to or from the adjacent aquifer.

Question 16

aquiclude

Answer 16

very reduced storage, cannot transmit groundwater, impermeable.

Question 17

unconfined aquifer

Answer 17

water table aquifer or phreatic aquifer
directly connected to water level, upper layer is the water table which is free to rise and fall.

Question 18

confined aquifer

Answer 18

restricted by 2 layers of aquitard. Water pressure is >atm.

Question 19

artesian well

Answer 19

if well is drilled through superposed aquitard into aquifer, water is under enough pressure to rise. If aquiclude is is above, pressure is even higher. A spring forms. An artesian well is when water rises till above the surface.

Question 20

semi-confined aquifer (leaky)

Answer 20

bounded by aquitard that does transmit water when hydraulic head above and below the leaky boundary are in disequilibrium. The head difference exists between aquifer A and B so water passes through aquitard to aquifer B. Aquifer B is then semi-confined.

Question 21

Karstic aquifer

Answer 21

controlled by rock dissolution

Question 22

What are the 3 forms of energy in GW?

Answer 22

kinetic energy –> velocity head
potential elevation energy –> datum head
pressure energy –> pressure head

Question 23

Kinetic energy

Answer 23

gained through motion/ velocity
E=1/2mv^2
velocity head = v^2/2g

Question 24

Potential Energy

Answer 24

measured with respect to the datum (normally NAP)
z meters above datum, particle has z energy

Question 25

pressure energy

Answer 25

by existing pressure, measured using piezometer
h = pressure/ weight (head)

Question 26

Total energy/ head

Answer 26

teh sum of kinetic, potential and pressure.

Question 27

Bernoulli’s equation

Answer 27

hydraulic head (sum of energies) is constant for an incompressible liquid

Question 28

simplification of total energy/head

Answer 28

gw has small velocity, lots of P so velocity head is removed.

Question 29

Porosity

Answer 29

the ratio of volume of void space to the total volume. Porosity determines how much watercan be held.
determines aquifer/tard classification
amount of water to saturate fixed volume

Question 30

volume for porosity

Answer 30

void volume/ total volume

Question 31

primary porosity

Answer 31

developed during rock formation
large in unconsolidated rock
small in unconsolidated rock
very small in highly consolidated rock

Question 32

examples of unconsolidated rock

Answer 32

sand, silt, gravel

Question 33

consolidated rock examples

Answer 33

sandstone, siltstone, conglomerate

Question 34

2 types of forcing

Answer 34

burial - new sediments over old
lithification - increased pressure and temperature

Question 35

secondary porosity

Answer 35

voids formed due to subsequent tectonic processes. Mainly in consolidated rocks - fractures develop due to movement of earth’s crust. Widened by dissolving processes (Cavities) This can be dissolution, fracturing, faulting.

Question 36

other names for primary and secondary porosity

Answer 36

matrix porosity - primary
fracture porosity - secondary

Question 37

types of rocks and their primary porosity

Answer 37

crystalline rocks (metamorphic and igneous) have low primary porosity
volcanic rocks have higher primary porosity

Question 38

in UNCONSOLIDATED rock, what determines primary porosity

Answer 38

size of grain/ rock fragments - independent of grain size if same pakcing
sorting of grains
arrangement - cubic or rhombus packing
shape of grain

Question 39

how does sorting affect porosity?

Answer 39

high porosity - well sorted
low porosity - poorly sorted

Question 40

in CONSOLIDATED rock, what determines the primary porosity?

Answer 40

all of the above and
compaction
cementation