Groundwater

Question 1

how is earths water distributed?

Answer 1

Oceans: 97.2%
Glaciers: 2.15%
Groundwater: 0.62%
Rivers and lakes: 0.02%
Soil moisture: 0.005%
Atmosphere: 0.001%

Question 2

What is groundwater?

Answer 2

Water below Earth’s surface, in pore spaces

Resides mostly in a zone of continuously saturated sediment or rock defined by being below the ‘water table’

Question 3

The shape of the water table usually mimics the …

Answer 3

surface topography

Question 4

what is the residence time of underground water?

Answer 4

280 years

Question 5

why is underground water important?

Answer 5

residence time
sea level
chemical weathering

Question 6

why did sea levels fall by 5mm in 2010-2011?

Answer 6

increase in water mass on continents

groundwater recharged by increased precipitation

Question 7

why is groundwater not a renewable resource?

Answer 7

Long residence (& recharge) times
Depleted aquifers cannot usually be replenished within the human life span
Supply & demand management

Question 8

how do groundwater systems recharge?

Answer 8

by precipitation, infiltration & percolation

Question 9

where do groundwater systems store water?

Answer 9

in deep aquifers

Question 10

where do groundwater systems discharge water?

Answer 10

to surface (springs & river baseflow)

Question 11

water will flow from…

Answer 11

higher pressure (hydraulic head) to lower pressure

Question 12

What controls groundwater flow?

Answer 12

1. Substrate
–porosity & permeability
2. Pressure differences
–due to weight of water at higher levels
3. Elevation differences
–potential energy (gravity)

Question 13

How does groundwater flow?

Answer 13

–from areas of high pressure →low pressure
–water moves down where water table is high due to ↑pressure
–then upward beneath areas with low pressure

Question 14

what is hydraulic gradient?

Answer 14

slope of water table

Question 15

where does water move when water table elevation is high (high pressure)?

Answer 15

down

Question 16

How fast does groundwater flow?

Answer 16

Rates: ~ 1 m/day –1 m/yr

Question 17

what does flow speed depend on?

Answer 17

(1) Slope of water table (hydraulic gradient)

(2) Permeability (hydraulic conductivity

Question 18

what is the equation for flow speed?

Answer 18

Flow speed (m/s) = hydraulic gradient x hydraulic conductivity (m/s)

Question 19

what is porosity?

Answer 19

% volume of pore space in rock/sediment/soil (how much water the substrate can hold)
Space between mineral grains, fractures etc
Moisture-holding capacity
E.g., 30-50% for most soils

Question 20

what is permeability?

Answer 20

(how easily can water flow in the substrate)
Pore shape and “interconnectedness”
- ability of substrate to transmit water

Question 21

how does groundwater weather rock?

Answer 21

Groundwater dissolves carbonates by dissolution weathering
Groundwater flow transports dissolved ions
Precipitation from groundwater to form stalactites etc
- water loses dissolved CO2 and evaporates, leaving calcite behind

Question 22

what is an aquifer?

Answer 22

permeable region that transmits groundwater freely (such as sands, gravels, fractured rock)

Question 23

what is an aquitard?

Answer 23

impermeable layer that hinders or prevents water movement (such as clay)

Question 24

where does natural groundwater discharge occur?

Answer 24

where water table intersects surface: rivers, lakes, springs..

Question 25

how is groundwater used by humans?

Answer 25

Wells (drinking, irrigation) - humans drill into water table

Pumping lowers local water table and results in a cone of depression in the water table around a well

Question 26

what are artesian wells?

Answer 26

Water rises on its own above the level of the aquifer (under pressure)

Question 27

what impact do humans have on Groundwater(due to extraction & surface activities)?

Answer 27

(1) Aquifer depletion
(2) Reduced base flow to rivers (effect on ecosystems, e.g., salmon)
(3) Ground subsidence
(4) Contamination

Question 28

what is ground subsidence?

Answer 28

Surface subsides due to groundwater removal - subsides due to compaction of sediment &/or erosion of substrate
-> irreversible loss of aquifer structure & storage

Question 29

why is the leaning tower of Pisa leaning?

Answer 29

built on unstable sediments… tilting due to ↑groundwater use

Question 30

how does contamination of groundwater occur?

Answer 30

Sewage, farm waste, industrial pollutants, mine waste may percolate into aquifers

Question 31

how is contamination of groundwater usually detected?

Answer 31

by people drinking contaminated water -> illness

Question 32

what is an example of contamination of groundwater?

Answer 32

Walkerton, ON tragedy in 2000 – groundwater contaminated with E. coli bacteria from farm waste

Question 33

what are Victoria’s water resources?

Answer 33

Deception and Sooke reservoirs, saddle dam
CRD watershed: large area with restricted access, to protect groundwater and reservoirs
2001: storage capacity ↑from 52 million m3 to 93 million m3

Question 34

what are some examples of Mitigation against human impacts in Victoria?

Answer 34

(1) Controls on groundwater extraction (as of Jan 2016, require license in BC for non-domestic well)
(2) Observation wells
(3) Regulation to prevent contamination, particularly in vulnerable areas
4) Strategies to improve infiltration of run-off
e. g. City of Victoria Rainwater Rewards Program, rain gardens