Topic 4: Groundwater

Question 1

what is an aquifer?

Answer 1

a geological unit saturated with water able to store and transmit water.

Question 2

Modern groundwater vs young groundwater

Answer 2

modern:
- -less than 50 years since recharge
- -most vulnerable to global environmental change
young:
- -less than 100 years since recharge

Question 3

groundwater use in BC

Answer 3

25% of BC population
45% of public water systems
derived mainly from infiltration and snow melt, recharge is seasonally variable

Question 4

groundwater use in USA

Answer 4

over 62% of groundwater extraction goes towards agriculture.

$20 Billion a year

Question 5

GRACE satellite purpose

Answer 5

helped make shallow groundwater drought indicator

Question 6

4 types of streams in relation to groundwater

Answer 6

• -gaining stream: water table above stream height
• -flow through stream: water table higher and water flow through from one side to the other
• -perched losing stream: water table below stream
• -losing stream: water table connected to stream and water flowing out

Question 7

unconfined aquifer

Answer 7

open to atmosphere, top of the saturated zone and is free to fluctuate. fluvial sediments involved.

Question 8

confined aquifer

Answer 8

saturated geologic zone overlain by confining layer
pressures are greater than atmospheric pressure
groundwater does not cycle as fast
groundwater ages can be greater than 10,000 years
receives water from smaller area

Question 9

Aquitard vs aquiclude

Answer 9

Aquitard: does not transmit significant amounts of water, very low hydraulic conductivity, could have significant storage capacity/porosity
Aquiclude: does not transmit any water, NO hydraulic conductivity and little to no porosity.

Question 10

what 2 things do aquifers serve as?

Answer 10

• -reservoirs for groundwater storage

- -pipelines for groundwater movement

Question 11

what does porosity depend on

Answer 11

shape, arrangement and degree or sorting

Question 12

specific yield

Answer 12

volume of water that can freely drain from a saturated rock or soil under the influence of gravity

Question 13

specific retention

Answer 13

volume of water retained by surface tension forces as films around individual grains and capillary openings

Question 14

list the 3 ways recharge inputs are transferred

Answer 14

1. flow to adjacent areas via throughflow
2. re-surface as return flow (springs) or baseflow (rivers)
3. long term storage in deep aquifers

Question 15

what is hydraulic head

Answer 15

h: measure of mechanical energy at a location- measured from base to water height

Question 16

what is elevation head

Answer 16

z: elevation above some chosen reference level. from middle of well screen to bottom of ground

Question 17

what is pressure head

Answer 17

P: to define water pressure at free interface between air and water as zero, measured from top of water table to middle of well screen.

Question 18

general rule for groundwater flow

Answer 18

1. water table reflects topography, deepest below uplands and shallow in valley
2. equipotential contours lines perpendicular to divides, parallel to boundaries.
3. streamlines perpendicular to equipotential contour lines
4. both horizontal and vertical flow components (generally down in uplands and up in lowlands)
5. flow nets complicated by changes in geology an topography

Question 19

what are equipotential contours

Answer 19

lines of equal hydraulic head

Question 20

what is darcys law

Answer 20

equation that describes the flow of a liquid through a porous medium

Question 21

what is hydraulic gradient

Answer 21

gradient slope of the top of the groundwater table that indicates the direction of movement

Question 22

T or F: groundwater flows in all directions

Answer 22

True, groundwater flows in all direction along potentiometric gradient from H to L

Question 23

vertical hydraulic gradient

Answer 23

determined from h levels between wells or piezometers

Question 24

horizontal groundwater flow

Answer 24

piezometric surface map of h contours. i=delta h/delta x

Question 25

what are groundwater flow nets and why are they useful?

Answer 25

they are lines of equal hydraulic head. useful for determining flow direction, distance and travel times

Question 26

conditions needed for effective recharge

Answer 26

soils should be permeable to conduct infiltration
vadose (unsaturated) zone must be permeable and free from clay layers
aquifer must be unconfined, permeable and thick to avoid groundwater mounds
groundwater table must be deep, beyond 10m below ground surface

Question 27

what is artificial recharge

Answer 27

practice of artificially increasing the amount of water that enters a groundwater reservoir.

Question 28

purposes for artificial recharge

Answer 28

conserve and dispose of runoff waters
supplement natural recharge of groundwater
reduce of balance salt water intrusion
suppress ground subsistence

Question 29

suitable infiltration sites

Answer 29

flood plains, alluvial fans, sand dunes, weathered zones, glacial outwash plains, permeable vadose zones

Question 30

importance of groundwater

Answer 30

• water supply
• supports aquatic ecosystems, moderates water temperature
• geologic processes

Question 31

what year did hydrogeology emerge as a distinct branch of science from hydrology and geology?

Answer 31

1800

Question 32

what are the key hydrological question you want to ask when there is a risk for site contamination?

Answer 32

1. what is the geology underlying the area?
2. what are the contaminants?
3. which way is groundwater flowing?
4. how long will it take for contaminants to reach the stream?

Question 33

Darcy’s law is applicable to which type of flow? turbulent or laminar?

Answer 33

laminar.