Increasing Water Supply (AQA A Level Geography)

• Balancing water demand with supply can be met by:
• Increasing supply
• Reducing demand 
• A combination of both
• Methods of increasing storage capacity can be large-scale or small-scale
• Whatever method chosen comes with pros and cons

Methods of Water Catchment and Storage

Method	Scale	Examples	Pros	Cons
Reservoirs - water captured naturally in drainage basins can be stored in artificial lakes, built by damming a valley	Large - water stored for use at regional or national scale	Three Gorges Dam, Yangtze river, China Aswan Dam, Nile River, Egypt	Controls flooding downstream by regulating river flow Huge volume of water can be stored and used in industrial, agricultural and domestic settings HEP power can be generated by turbines within the dam Recreational uses of the lake to include fishing and water sports	High economic cost of building and maintaining scheme Flooding of land to create reservoir destroys habitats and can displace communities Alteration of the natural river regime causes sediment to build up in the lake Reduction of sediment available for deposition downstream Increase in erosion downstream Can create microclimate around the lake, affecting humidity and wind speeds
Rooftop rainwater harvesting - rain falling on roofs of buildings can be captured and stored in filtering tanks under gardens	Small - water used in domestic settings for individual households or small communities	In Bangalore, India, it is mandatory for buildings with a footprint of more than 200㎡ to harvest and utilise rainwater for internal use	Relatively cheap and easy to implement and maintain Provides self-sufficiency for households	Needs to have a relatively reliable supply of rainfall Only really effective for domestic settings

• Water diversion involves transferring captured water from areas of surplus to areas of deficit
• Water can be drawn from
  • Aquifers
  • Rivers
  • Reservoirs
• And pumped between drainage basins by
  • River diversions
  • Aqueducts
  • Canals
  • Pipelines

• Examples include:
• The Sindh Province in Pakistan
• A network of irrigation canals transferring water from the river Indus to cropland 
• High evaporation rates in the canals reduces the effectiveness  
• China’s north-south diversion project 
• Planned to complete in 2050
• To divert water 44.8 billion cubic metres of water annually from southern rivers to the population centres of the arid north
• Expected to cost $62bn – more than twice as much as the Three Gorges Dam
• Advantages of these schemes include:
• Allows water to be supplied to regions that are water stressed
• Localised droughts can be quickly addressed
• Water can be transferred in large volumes to be used for agricultural, industrial and domestic purposes
• Disadvantages of these schemes include:
• They tend to be very expensive to build and maintain
• Tend to be large-scale and so can have large impacts on the environment:
• Can lead to major environmental deterioration if not sustainably managed 
• E.g. the Aral Sea in Central Asia
• Reduced in size by 90%
• Due to decades of heavy irrigation from river transfers in surrounding countries
• Salt has been brought to the surface making the land infertile
• Fishing industry has been destroyed

Desalination

• Involves the removal of salt from seawater to make it drinkable
• Various methods either using heat or membranes to separate salt from the water
• The two main methods are:
  • Distillation
    • The traditional way
    • Seawater heated and boiled
    • Steam produced is condensed 
    • Salt left behind in boiler

• Reverse osmosis
• Seawater filtered at high pressure
• Small tubes syphon off drinkable water
• Saline solution left behind is pumped back to sea
• Both methods are still used but reverse osmosis is more modern and efficient
• Desalination plants are expensive to build and maintain, so mainly operate in HICs in water-stressed regions
• E.g. Saudi Arabia - Water desalination has doubled over the past decade to reach 2.2 billion ㎥ in 2021, up from 1.1 billion in 2010
• Oman, UAE, Australia and USA are the other biggest users of desalination
• UK has a plant in Beckton, East London, which provides drinking water for 400,000 households

The pros and cons of desalination

Environmental Impacts of a Water Supply Scheme

• The Aswan Dam was completed in 1970 across the Nile River in Southern Egypt
• It was built as a solution for rising demand for water
• Its reservoir, Lake Nasser, is estimated to store over 132km3 of water
• The scheme aimed to reduce flooding downstream by regulating the flow of the Nile
• It also provided irrigation for vast areas of arid farmland surrounding the lake
• An HEP plant in the dam initially provided a renewable source of electricity to half of Egypt’s population
• Rising demand for electricity has meant that this proportion has fallen to one tenth today
• However critics of the dam point to several negative environmental impacts of its building and operation

Environmental impacts of the Aswan Dam