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Water World

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The Hydrological Cycle

The Earth's water is always on the move around the Hydrological Cycle.
  • 99% of the Earth's water is stored in oceans, ice caps and glaciers
  • 1% of the Earth's water is stored in lakes, rivers, ground, atmosphere, marsh and vegetation.
 Surface FlowThrough Flow Groundwater Flow 
 Rain falls onto the ground and flows on the surface into rivers and lakes. Rainwater is soaked into the soil (infiltration) and flows slowly to rivers. Rain water is soaked into rocks below the soil. It moves slowly through cracks and joints or airspaces (pores)

Hydrological Processes

There are three hydrological processes you need to know...
  • Evaporation - when water warms up and returns to the atmosphere as water vapour.
  • Condensation - when water vapour cools and forms tiny water droplets, sometimes forming visible clouds
  • Precipitation - when the tiny water droplets previously formed collide and grow until they fall to the ground as rain or snow.
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Climate and water supplies

Unreliable water supplies and their impacts

Here are the three main reasons why water supplies may be unreliable...
  • There may be specific wet and dry seasons - In the Sahel in Africa, they have a long dry period which causes the ground to become hard. In the short wet period the Sahel gets, there is a lot of water run-off so little water is stored.
  • There may be weather cycles where an area may get several dry years followed by several wet years - recently in the Sahel, they have been experiencing several years of droughts, leading to serious food shortages.
  • Global warming and a continuing rise in temperatures - Dry places like the Sahel will get drier, and wet places like here in the UK will get wetter.

Case Study - South-West USA

  • South-west USA is a very arid area with a lot of dependency on the Colorado River which is their main source of water, including the irrigation of crops
  • Climate Change poses the threat of making the area even drier. Las Vegas experienced drought years in 2002, 2004 and 2007.
  • This threat of climate change will lead to restrictions being enforced on taking water from the Colorado River. This will have a knock-on effect of people having less water for irrigation, meaning fewer crops and artificially created green areas. 
  • The lack of water will also create problems for the rapidly increasing population of the area. Arizona had a population increase of 25% between 2000 and 2010.

Effect of Climate Change on Asia

  • Countries in Asia, such as China, India and Vietnam, depend greatly on their water from the melting glaciers in the Himalayas.
  • The Long-term impacts of climate change could result in all the Himalayan glaciers melting leading to severely reduced water supplies.
  • The Short-term impacts of climate change could result in an increase in glacial melt in the Himalayas leading to seasonal stress on agriculture for example.

Threats to the Hydrological Cycle

There are many things which us humans are doing which is impacting on the hydrological cycle.
 Causes of River Pollution Managing river pollution
  • Untreated sewage pumped into rivers can lead to serious diseases such as Cholera and typhoid.
  • Intensive agriculture which releases fertilisers, pesticides and herbicides into the local water systems can poison wildlife and affect water quality.
  • Waste chemicals which are leaked from factories can poison wildlife and affect water quality
  • Plastic bags and other non-biodegradable waste can kill wildlife, clog up water ways and affect water quality.
  • Sewage is treated before it can be pumped into rivers
  • Farmers and land-owners regulate their use of fertilisers and chemicals to reduce pollution and damage
  • Factories dispose of their chemical waste before returning water to the river.
    • In the UK, the Environment Agency imposes heavy fines on any factory which releases chemical waste into the environment.
  • Plastic and all other recycable waste is sent to recycling centres to be recycled rather than being dumped in rivers.
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Large-scale water management

Water management schemes try to deal with the water supply problems a place might face. These large scale water management schemes:
  • are expensive to build and maintain
  • cover large areas
  • are organised by local or national government
  • usually consist of dams and reservoirs being created

Developed world case study - The Colorado River, USA

 BenefitsDisadvantages 
  • Reduces flooding that would normally occur in the summer, and reduces drought that would normally occur in the winter
  • Electricity is produced by the dam for local towns, farms and factories
  • Water is stored behind the dam which can be used for irrigation and for supplying growing cities such as Las Vegas.
  • There is year-round supply of clean water for US cities.
  • Land is lost to flooding when making the dams.
  • Sediment has built up behind the dams which affects the workings of the Hydroelectric Power (HEP) generation.
  • Less sediment flowing down the river has disrupted the habitat for native fish.
  • Also, the lack of sediment means sandbanks have shrunk which is also impacting animals and their habitats.
  • Less water downstream in Mexico

Developing world case study - The Three Gorges Dam, China

 BenefitsDisadvantages 
  • Reduced risk of flooding for homes, farms and factories along the Yangtze River
  • Water stored behind the dam is available for irrigation
  • Hydroelectric power (HEP) is generated by turbines in the dam. It's the world's largest capacity HEP station.
    • The electricity it produces means China saves 31 million tonnes of coal each year and thier overall greenhouse gas emissions has reduced
  • The river is deeper and more navigable for ships, so it has improved transport and trading in China.
  • Good farmland has been lost because of the dam.
  • Over 1 .3 million people were forced to move their homes as towns and villages disappeared under water.
  • Important cultural and archaeological sites were lost.
  • There is an increased risk of landslides in some places.
  • The project was very expensive, $US 22.5 billion, but some people estimate the actual cost to be as high as $US 50bn.
  • Sediment is building up behind the dam.
  • There is no sediment to maintain river banks resulting in downstream areas becoming more at risk to flooding.
  • Important wetland areas have been destroyed.

Small Scale Water Management

In the developing world, you are more likely to find small scale, intermediate technology solutions to any unreliable water problems. These solutions are relatively cheap to build and maintain, cover small areas, are organised by the local people in conjunction with charities and local organisations, and help local people access clean water and increase water storage safely.
  • Wells - Wells are dug to reach underground water supplies. They are lined with concrete and have a concrete lid to prevent pollution by sewage.
  • Hand pumps - A more efficient way of reaching underground water where there is less chance of water becoming contaminated.
  • Rain barrel - Water barrels collect rainwater from gutters and roofs can can be stored and used in times of droughts. This is called water harvesting. The water stays clean in the covered barrel.