Sources of water

Question 1

Importance of water availability

Answer 1

Allows development of society

Question 2

Sources of abstractable water

Answer 2

Rivers
Reservoirs
Aquifers
Seawater

Question 3

Rivers

Answer 3

Generally most convenient source
Short residence time means self cleaning
Natural contaminants rarely a problem
Human pollutants problematic in high density

Question 4

Features affecting usefulness of a river

Answer 4

River discharge
Flow fluctuations
Level of natural contaminants
Pollutants from human activities

Question 5

Reservoirs

Answer 5

Allow for storage during surplus months

Require a dam built in a suitable place

Question 6

Factors affecting reservoir placement

Answer 6

Topography
Geology
Catchment area
Water supply
Existing land use
Pollution risk
Sedimentation 
Infrastructure
Estuarine barrages

Question 7

Topography

Answer 7

Ideal topography is narrow exit to a large basin
Most cost is building the dam across an exit
Large basin holds more water with less cost

Question 8

Geology

Answer 8

Must be impermeable rock below reservoir
Can’t have faults or seismic activity
Rock must be strong

Question 9

Catchment area

Answer 9

Ability of reservoir to provide water controlled by surrounding area
Ensures water supply if rain hasn’t fallen recently

Question 10

Water supply

Answer 10

Ideal rainfall/river inflow is regular and large

Hot/dry climate causes excessive evaporation

Question 11

Existing land use

Answer 11

Land to be flooded can’t be important
Losses and benefits must be balanced
UK large urban areas/sensitive habitats would be protected
UK agricultural land would be flooded

Question 12

Pollution risk

Answer 12

Main threats are toxins from industries/agriculture
Biodegradable pollutants eg. manure aren’t as bad
Flooded areas with lots of vegetation could lead to anaerobic decomposition
Anaerobic decomposition leads to methane, global warming

Question 13

Sedimentation

Answer 13

Soil erosion leads to turbid water

Sediments settle and reduce capacity of reservoir

Question 14

Infrastructure

Answer 14

Workers, access routes, materials needed to make dam

A site with convenient access could be chosen over more water

Question 15

Case study- Water demand in Devon and Cornwall

Answer 15

Increasing populations demand more water
Water usage rises with affluence
Water usage rises as more appliances use water
Summer has lowest supply but highest demand
Best water source for demand is reservoirs
Best reservoir sites in AONBs/national parks
Other reservoir site are a compromise

Question 16

Estuarine barrages

Answer 16

Dam across an estuary
Creates freshwater lake for supplies
Eg. Ijesselmeer in the Netherlands
Few have ever been built
High pollution risk
Interferes with navigation

Question 17

Environmental effects of reservoirs

Answer 17

Habitat change
Changes in river flow
Sedimentation
Reservoir microclimate

Question 18

Habitat change

Answer 18

Flooding destroys previous habitat
Creates new, possible sensitive, habitats
Wetlands are uncommon
Can create more valuable habitats than before
Dam acts as a barrier to migratory fish
Eg. salmon
Dam may prevent recolonisation

Question 19

Changes in river flow

Answer 19

Piped water leaves flow same but smaller
Water used to regulate river flow in surplus/drought
Reduces flood risk
Reduces periods of low flow essential for breeding
Eg. turtle eggs in sandbanks
Inhibits meander formation

Question 20

Sedimentation

Answer 20

Sediments in reservoir won’t get downstream
Loss in fertilisation of flood plains
Loss of riverbanks/coastlines
Increase in erosion

Question 21

Reservoir microclimate

Answer 21

Large body of water changes local climate
high heat capacity means less temperature fluctuations
Warmer winters/cooler summers
Less friction over water so higher wind speed
Greater evaporation causes higher humidity, cloud coverage, precipitation downwind

Question 22

Main features of aquifers

Answer 22

Porosity
Permeability
Suitable geological features

Question 23

Porosity

Answer 23

Measure of how much of a rock is space
More porosity means more water held
Eg. chalk, limestone, sandstone

Question 24

Permeability

Answer 24

The ease of which fluids flow through a rock
Determined by interconnections between spaces
Eg. clay has high porosity but low permeability

Question 25

Suitable geological features

Answer 25

Impermeable rock below water bearing rock
Eg. granite, clay
Some permeable rock above for recharge

Question 26

Aquifer overuse

Answer 26

Abstraction exceeding rate of recharge
Reduced supplies
Subsidence
Changed surface hydrology
Ecological impacts
Saltwater incursion

Question 27

Reduced suppies

Answer 27

Volume of water available for abstraction is reduced

Human activities reduced/stopped

Question 28

Subsidence

Answer 28

Loss of water causes compaction of rocks
Compaction causes subsidence at surface
Can cause serious damage to buildings/pipes
Looks like sinkhole

Question 29

Changed surface hydrology

Answer 29

Rivers/lakes/marshes fed by aquifer streams
Overuse reduces water table
Reduced water table reduces flow of aquifer streams
Flow to wetlands dries up
Wetlands dry up

Question 30

Ecological impacts of aquifer overuse

Answer 30

Plants with high water requirement outcompeted

The outcompeted species collapses the food chain

Question 31

Saltwater incursion

Answer 31

Sidewards flow of freshwater into sea prevents seawater entering aquifer
Reduced water in aquifer lowers water table
Lowered water table allows seawater into aquifer
Salt contaminates water
Water is no longer suitable for irrigation

Question 32

Seawater

Answer 32

Desalinisation is expensive

Only used in countries where freshwater supplies are inadequate

Question 33

Case study- Ogallala aquifer, USA

Answer 33

Lies under 8 states of mid-west USA

Supplies 1/4 of irrigated farmland in USA