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Flashcards in Groundwater Deck (43):
1

Roughly _____% of Canada's population is reliant on groundwater

25-40%

2

Define Groundwater

water that lies beneath the surface

3

Ground water makes up for __% of the hydrosphere's fresh water, while glaciers make up for ___%

22% and 77%, respectively

4

___% of total precipitation infiltrates the ground and sends up as ground water

15%

5

True or False: ground water is static

False; it is slow moving

6

True or False: groundwater is found most commonly in underground lakes and rivers

True, but barely. It can occur, but is extremely rare

7

Where is groundwater most commonly found

pores of sediment and soil
fractures of bedrock

8

Porosity

percentage of voids or pore space (vs total volume)

9

What is porosity used to determine?

How much groundwater can be stored

10

How to measure porosity

Take a column with a toal volume of 1000 mL and fill it with dry sand (dry sand has a porosity filled with air). replace the air with water. The porosity=volume water/Volume total

11

Permeability or Conductivity

Capacity of rock or sediment to transmit a fluid
(connected pores give a rock permeability)

12

Specific yield

% that can drain by gravity

13

Specific retention

% that cannot drain by gravity

14

Distribution of ground water is found in what three places?

1) Unsaturated zone
2) Water Table
3) Zone of saturation

15

Unsaturated zone

-above water table
-voids filled by water and air
-water is under suction (negative pressure) due to capillary forces (think TLC)
-water cannot be pumped by wells

16

Water Table

-Upper limit of zone of saturation
-surface of water level in ground
-depth varies seasonally

17

Zone of Saturation

-below water table
-all voids are filled with water
-water is under positive pressure and can be sucked up by wells

18

Pressure distribution

unsat:
a) Patmos. P
b) water under (+) pressure

19

What factors control infiltration?

1) precipitation
2) slope
3) geological material
3) vegetation

20

In what three places is groundwater stored?

1) Aquifer
2) Acquitard
3) Aquiclude

21

Aquifer

permeable rock layer or sediment that stores and transmits groundwater

22

Acquitard

semi-permeable rock layer

23

Aquiclude

impermeable rock layer (exCLUDEs water)

24

Types of aquifers

Unconfined and confined

25

Unconfined aquifer

-no confining layer
-groundwater is not under pressure
-top of water table moves freely up and down

26

Confined aquifer

-sandwiched between 2 confining layers (usually inclined to allow recharge)
-groundwater is under pressure
-top of water table is above confined aquifer

27

Types of wells

Non-flowing artesian well and flowing artisan well

28

Non-flowing artesian well

water table (pressure surface) of a confined aquifer lies below ground level (pressure is not great enough to bring water to the surface)

29

Flowing artesian well

Water table of a confined aquifer rests above ground level; water reaches ground surface using natural pressure of the confined aquifer

30

What is the general pattern of movement?

recharge (high) --> discharge (low)

31

True or False: velocity is highest nearest the surface

true

32

Darcy's Law states:

States that if permeability remains uniform, the velocity of groundwater will increase as the slope of the water table (hydraulic gradient) increases

33

Darcy's Law equation

v=-(K/fancy n)(i), where K = hydraulic conductivity, n = porosity, i=hydraulic gradient=driving force, v=velocity

34

Ground water and stream interactions

1) gaining streams
-gain water from the inflow of groundwater through streambed
2) losing streams
-loss of water to the groundwater system by outflow through streambed

35

The water table is ____ than the stream bed in the gaining streams interaction

higher

36

The water table is ____ than the stream bed in the losing streams interaction

lower
-zone of aeration present

37

Sources of groundwater contamination

-road salt
-fertilizers
-pesticides
-chemical and industrial materials
-bacteria and viruses

38

What are some problems associated with groundwater withdrawal?

Sewage contamination
-sewage often becomes purified as it passes through the aquifer composed of sand or permeable sandstone. However, in extremely permeable aquifers (ie. coarse gravel or fractured bedrock), the groudwater may travel long distances without being cleaned

Saltwater contamination
-excessive groundwater withdrawal causes saltwater to be drawn into wells

39

What are the consequences of excessive pumping?

1) drawdown (lowering) of the W.T
2) cone of depression in the WT

40

subsidence

Ground shrinks when water is pumped from wells faster than the recharge process can replace it

41

Geysers

intermittent surface emission of hot water
occur when groundwater heats, changes to steam, and errupts

42

Erosional features of groundwater

-caves (underground cavity)
-Karst topography (typically form in limestone bedrock) (ie. caves and sinkholes)

43

Depositional features

-Groundwater is often mildly acidic, so it dissolves rocks (particularily limestone).
-if rxn reverts and CO2 escapes, CaCO3 is deposited, creating stalactite (point down), stalagmite (point up), column/pillar etc