Sources of water Flashcards
Importance of water availability
Allows development of society
Sources of abstractable water
Rivers
Reservoirs
Aquifers
Seawater
Rivers
Generally most convenient source
Short residence time means self cleaning
Natural contaminants rarely a problem
Human pollutants problematic in high density
Features affecting usefulness of a river
River discharge
Flow fluctuations
Level of natural contaminants
Pollutants from human activities
Reservoirs
Allow for storage during surplus months
Require a dam built in a suitable place
Factors affecting reservoir placement
Topography Geology Catchment area Water supply Existing land use Pollution risk Sedimentation Infrastructure Estuarine barrages
Topography
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
Geology
Must be impermeable rock below reservoir
Can’t have faults or seismic activity
Rock must be strong
Catchment area
Ability of reservoir to provide water controlled by surrounding area
Ensures water supply if rain hasn’t fallen recently
Water supply
Ideal rainfall/river inflow is regular and large
Hot/dry climate causes excessive evaporation
Existing land use
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
Pollution risk
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
Sedimentation
Soil erosion leads to turbid water
Sediments settle and reduce capacity of reservoir
Infrastructure
Workers, access routes, materials needed to make dam
A site with convenient access could be chosen over more water
Case study- Water demand in Devon and Cornwall
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
Estuarine barrages
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
Environmental effects of reservoirs
Habitat change
Changes in river flow
Sedimentation
Reservoir microclimate
Habitat change
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
Changes in river flow
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
Sedimentation
Sediments in reservoir won’t get downstream
Loss in fertilisation of flood plains
Loss of riverbanks/coastlines
Increase in erosion
Reservoir microclimate
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
Main features of aquifers
Porosity
Permeability
Suitable geological features
Porosity
Measure of how much of a rock is space
More porosity means more water held
Eg. chalk, limestone, sandstone
Permeability
The ease of which fluids flow through a rock
Determined by interconnections between spaces
Eg. clay has high porosity but low permeability
