The Earth's water is always on the move around the Hydrological Cycle.
Surface FlowRain falls onto the ground and flows on the surface into rivers and lakes.
Through FlowRainwater is soaked into the soil (infiltration) and flows slowly to rivers.
Groundwater FlowRain water is soaked into rocks below the soil. It moves slowly through cracks and joints or airspaces (pores)
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.|
Here are the three main reasons why water supplies may be unreliable:
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.||Sewage is treated before it can be pumped into rivers|
|Intensive agriculture which releases fertilisers, pesticides and herbicides into the local water systems can poison wildlife and affect water quality.||Farmers and land-owners regulate their use of fertilisers and chemicals to reduce pollution and damage|
|Waste chemicals which are leaked from factories can poison wildlife and affect water quality||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.|
|Contain basaltic magma which is very hot with low silica and gas content||Made up of layers of thick lava and ash|
|Plastic bags and other non-biodegradable waste can kill wildlife, clog up water ways and affect water quality.||Plastic and all other recycable waste is sent to recycling centres to be recycled rather than being dumped in rivers.|
Water management schemes try to deal with the water supply problems a place might face. These large scale water management schemes:
|Reduces flooding that would normally occur in the summer, and reduces drought that would normally occur in the winter||Land is lost to flooding when making the dams.|
|Electricity is produced by the dam for local towns, farms and factories||Sediment has built up behind the dams which affects the workings of the Hydroelectric Power (HEP) generation.|
|Water is stored behind the dam which can be used for irrigation and for supplying growing cities such as Las Vegas.||Less sediment flowing down the river has disrupted the habitat for native fish.|
|There is year-round supply of clean water for US cities.||Also, the lack of sediment means sandbanks have shrunk which is also impacting animals and their habitats.|
|Less water downstream in Mexico|
|Reduced risk of flooding for homes, farms and factories along the Yangtze River||Good farmland has been lost because of the dam.|
|Water stored behind the dam is available for irrigation||Over 1 .3 million people were forced to move their homes as towns and villages disappeared under water.|
|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 project was very expensive, $US 22.5 billion, but some people estimate the actual cost to be as high as $US 50bn.|
|The river is deeper and more navigable for ships, so it has improved transport and trading in China.||There is an increased risk of landslides in some places.|
|Important cultural and archaeological sites were lost.|
|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.|
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.|