The hydrological cycle
Biosphere- the part of the earth and atmosphere in which living organisms exist
Lithosphere- the outer layers of the earth's surface (the crust and upper mantle)
The global hydrological cycle
Stores of water are linked by processes which transfer water into and out of them.
Precipitation follows a number of routes
- Some runs off over the surface (surface run off)
- Some seeps into the soil or rock
- Some collects as snow or ice
The lithosphere and biosphere both regulate the water cycle
- In the biosphere, trees intercept precipitation, and over half of it is then evaporated and transpired without even reaching the ground (GREEN WATER)
- Precipitation drips from leaves and also makes its way slowly into the river system
- It infiltrates the soil, flows as flowthrough, or into the permeable rock as groundwater
Infiltration- movement of water into the soil from the surface
Percolation- movement of water into underlying rocks
Groundwater storage- water stored in rocks following percolation
Saturation-when the soil is full of moisture
Water table- the level at which saturation occurs in the ground or soil
Inputs- things which enter the system
Outputs- things which leave the system
Transfers or flows- movements within the system
Stores- held within the system
Pressures on water supply
Water stress- when the demand for water exceeds the amount available during a certain period, when it is not good enough quality.
Physical- Shortages occur when demand exceeds supply
Economic- when people cannot afford water, even if it is available
Decline in water availability and quality
- Population growth -water supplies per person decreased by one third from 1970-1990. The demand for water is higher. (water supplies per person has thus decreased by one third)
- Agriculture- Population growth increases the demand for food and water needed for farming. The area of irrigated land doubled in the 20th century
- Climate change- this will affect rainfall, evaporation and thus availability. Places suffering from water shortages are likely to have lower rainfall.
Rain falls in only 1/2 months of the year
The length of the rainy season is variable
If rain comes in heavy downpours, water can be lost as surface runoff, and this can cause flooding
- Drought causes seasonal rivers and water holes to dry up and the water table to fall
- Drought is disastrous to the nomads who graze animals, and for subsistence farmers who rely on rain.
- Grasses die, and soil erosion and desertification follow, due to overgrazing by animals.
- Organic wastes such as domestic sewage consumes oxygen in the water and can kill organisms (agricultural/domestic)
- chemicals such as plastics and oil are highly toxic and at low concentrations can lead to the death of most life in the river
- suspended solids affect the colour of the water and it kills fish/shellfish
Pollution in LEDCs
The highest rates of water pollution are usually linked to the most rapid rates of economic growth e.g India and China. These countries are developing their energy sources rapidly and put economic growth before environmental protection.Cities are growing fast and the waste disposal system cannot meet the needs.
Polution in MEDCs
e.g Japan has taken steps to stop pollution. Tertiary and quaternary industries cause less water pollution. In the 1960s Japan's lake and rivers polluted. For example Minamata, mercury poisoning occurred in fish that people ate causing humans neurological problems. In the 1970s, the government produced standards to tackle pollution. Rivers entering Tokyo are almost free of pollutants
Human interference in the water cycle
- Deforestation- removing trees reduces transpiration, less green water. This can lead to a reduction in rainfall and possible desertification
- Leads to a loss of soil nutrients (soil erosion takes away the top layer)
- It cuts out the process of interception which can increase flash flooding and the siltation in rivers.
- Reservoir Building- In some parts of the world, natural lakes are drying up, artificial reservoirs can add new stores to the water cycle
- HEP generation can be achieved if the damn is high enough
- Problems with reservoirs include- the loss of land
- They can be a source if disease, (homes to insects such as mosquitoes)
- Vegetation drowned by the lakes decays and releases methane and carbon dioxide
- Over-abstraction -over-abstraction of water in the Thames Valley has led to a dramatic drop in river flow, causing some tributary streams to dry up, damaging the ecosystem
- droughts and housing demand in Southern England has led to increased use of groundwater supplies. This can lowered the water table across the Thames Basin, so the aquifer is not being used sustainably.
found in contaminated water or foods, or undercooked food
It causes vomiting, diarrhoea, eventual dehydration and death.
Is caused by a parasite, spread by the female mosquito, when bitten, the parasite enters the bloodstream, causing illness. The parasite multiplies in the red blood cell, causing light-headedness and fevers, sometimes leading to death.
Worms enter the body through contact with infested water. This can be by washing hands, washing foods, swimming, fishing etc.
People are weakened by the disease and therefore cannot work. People develop rashes, fevers, chills and muscle aches. Some eggs are trapped in the body tissues, resulting in damage to vital organs.
Large Scale water management projects
Three Gorges Dam Project, China
- Began construction in 1994
- Yangtzee River
- $40 billion
It was built to prevent flooding that used occur further downstream and to make more of the Yantzee river navigable to ships. It was also needed to produce HEP for China, and to ensure that there was a water supply, even in drier times. (however 66% of Wanxian city was flooded and 1.2 million people needed re-housing)
- 607ft high and 1.4 miles long
- between Chongqing and Sandouping
Impacts of the three gorges dam
- $11 billion to be paid in compensation to the people who have lost their home because of flooding, or other reasons,
- Fertile land was lost, and farmers lost jobs and had to relocate.
- Cultural sites of significance have been lost
- 1.4 million people had to be re-settled after homes were flooded
- There was an increase of sediment into the river, due to high levels of erosion. This sediment settles upstream due to a slower flow, affecting ecosystems e.g ENDANGERED RIVER DOLPHIN.
- sewage is not washed down and remains in the reservoir, carrying disease.
- HEP generated is the most any dam in the world creates, and reduce China's reliance on fossil fuels.
- More reliable water supplies for China's cities
- Jobs created in the construction of the dam
- The river can be used by ships carrying cargo, which reduces the reliance on road transport
Small scale water management projects
- Old Zhimkhana, a slum community built on the site of a disused railway station in Dhaka.
- No safe water or toilets
- NGO Prodiplan (WaterAid)
- Six deep tube wells have been constructed
- two new sanitation blocks provide toilets and water for washing
- These save people time and energy in collecting water
- The people there are not continually ill and the appropriate technology has allowed them to move out of poverty.
Sand Dams Kenya
- Excellent Development (Uk charity)
- In the rainy season, sand builds up behind the dam, and water is stored in the sand (underground) and can be accessed all year round
- Saves time as they people do not need to travel to collect water, more time for education
- Improves health, fewer water borne diseases
- It provides clean water and improves the environment