Water as a Resource

Question 1

NASA’s motto in the hunt for extraterrestrial life: “follow the water”

Answer 1

• Perfect solvent

- Water flows -> provides a way to transfer substances between cells and environment

Question 2

Where is the water?

Answer 2

Total water on Earth = 100%

• Oceans and salt lakes: 97.41%
• Ice and snow: 1.984%
• Groundwater: 0.592%
• Lakes and rivers: 0.0071%
• Soils, wetlands, and biota: 0.0059%
• Atmospheric water: 0.001%

Lots of water BUT only a tiny fraction by volume of the world’s water supply is available for human use

Question 3

Storage of Freshwater (2.5% of total)

Answer 3

• Ice caps and glaciers: 68.6% (not readily available)
• Groundwater: 30%
• Rivers and lakes: 1.4%

Question 4

Freshwater is not distributed equally on the surface, resulting in:

Answer 4

deserts, rainforests, and glaciers…

Question 5

Lakes hold less than 0.4% of the world’s freshwater

Answer 5

• 80% of the water stored in lakes worldwide is held in <40 large lakes.
• They are only important as local sources of water

Question 6

Rivers hold about 1% of the world’s freshwater

Answer 6

Rivers supply abundant water to cities:

• Hydroelectric power generation
• Household use
• Industrial use
• Agriculture
• Etc.

Question 7

In Canada, most of our water use is for:

Answer 7

power generation and industrial purposes

Question 8

Of the 38 billion m3 of water withdrawn in 2013, ~90% was returned to the

Answer 8

rivers and lakes of origin, 3.6billion m3 were consumed (consumed water cannot be used again immediately)

Question 9

Power generation uses ~27bil m3 of water;

Answer 9

2% is consumed

Question 10

Agriculture uses ~2bil m3 of water; 80-90% is consumed

Answer 10

Worldwide, agriculture extracts >6.4 trillion litres of water per day (82% for irrigation)

• This is suspected to increase to 56.4 trillion litres of water per day by 2050, BEYOND dependable flow of the world’s rivers
• Water availability is expected to limit pop growth in the 21st century

Question 11

In many areas, consumption exceeds local surface water supplies, so water must be imported or mined.

Answer 11

• It is estimated that 3000x more water is stored as groundwater in the upper 800m of the continental crust than water found in all the world’s rivers and streams
• About 30% of the population of Canada depends on groundwater

Question 12

Hydrogeologists

Answer 12

Groundwater geologists that specialize in distribution, circulation, and contamination of groundwater

Question 13

Misconception is that groundwater exists in vast, underground rivers and lakes

Answer 13

This is generally not true, except in karsted carbonate rocks

Question 14

Where is groundwater stored and how does it move?

Answer 14

Most groundwater is stored in pore spaces and fractures in rocks

Question 15

Outcrops

Answer 15

Areas of exposed rock that provide a glimpse of subsurface conditions that we can’t see otherwise. Fractures and pore spaces can be microscopic to macroscopic

Question 16

Porosity

Answer 16

Volume of empty space/total volume of rock (expressed as percent or fraction of 1)

• Shales can have higher porosity than sandstones, but the pore size is very small
• Primary porosity in limestones and other crystalline rocks may be very low, but secondary porosity (e.g vugs or fractures) may be high

Question 17

Permeability

Answer 17

A measure of the ability of a rock or sediment to transmit fluid. Related to the size and interconnectedness of pores or fractures

Question 18

The permeability of a medium is related to the porosity, but also to

Answer 18

the shapes of the pores in the medium and their level of connectedness.

High porosity, from high to low permeability: gravel, sand, silt, clay

Question 19

High permeability allows for lots of drainage, whereas low permeability

Answer 19

minimizes drainage

Question 20

Water that doesn’t run off enters porous rock through:

Answer 20

Infiltration.

- Fractured and porous rocks can store water

Question 21

If these rocks are permeable, they can also transmit water.

Answer 21

• Infiltrating water tends to percolate downwards (gravity)
• The pores fill with water until it is saturated
• The top of the saturated zone is called the water table
• Above the water table in the unsaturated zone, pores may contain a mix of water and air

Question 22

The shape of the water table mimics topography, but is subdued

Answer 22

The water table can move up and down with precipitation/drought withdrawal

Question 23

In some situations, groundwater contributes to the base flow of a stream

Answer 23

In others, streams contribute to the groundwater

- If an area is dry, the water table may be far below the stream (disconnected losing stream)

Question 24

Types of Streams

Answer 24

Gaining stream: base of stream is in the water table and gains base flow of water
Losing stream (connected): base of stream touches the water table but loses base flow
Losing stream (disconnected): base of stream does not touch the water table, losing base flow to ground and infiltrates down to water water

Question 25

Wetlands often occur where

Answer 25

The water table intersects the land surface

Question 26

Springs generally form where

Answer 26

The water table intersects a slope

Question 27

Aquifer

Answer 27

Saturated rock that contains and transmits “significant” quantities of water
- Depends on usage

Question 28

Unconfined aquifer

Answer 28

Recharged by water seeping directly from the ground above

- The level of the water can change over time

Question 29

Confined aquifer

Answer 29

Fully saturated and bound by ~impermeable layers above and below the aquifer

Question 30

How does water get into confined aquifers?

Answer 30

Recharge from other places

Question 31

What are some groundwater issues we are facing?

Answer 31

Contamination:
Acid mine drainage:
- acidic solution gets into surface water: harms terrestrial, vegetation, and aquatic systems, and weathering increases.
- Acidic solution gets into groundwater: difficult to recharge or fix once contaminated