The Three Gorges Dam

Factfile

DIMENSIONS: 181m high and 2.3km wide

AREA FLOODED: 632km(squared)

COST: £25.5 billion

BUILT: started 1994, finished 2009 

INCREASED DEPTH: 110 m (reduced to 80m when flood risk downstream)

RESERVOIR: Holds back 20 billion tons of water

ENERGY: 85 billion kilowatt hours a year by 2009

LOCATION: Yichang on the river Yangste. 

Positive impacts of the Three Gorges Dam:

Social

Tourist attraction - Provides income from visitors but also social and recreational benefits from those visiting the dam and reservoirs. 

Environmental

Cleaner and sustainable energy resource - This amount of reliable renewable power production capacity can keep China from generating electricity from fossil fuels which can harm the environment and eventually will run out. The dam is a stable source of great power that will continue after fossil fuels have run out.

Flood Control - The dam helps to manage and control the flow of the water and prevent flooding which has caused significant damage in the past. 

Economical 

Energy production - China is a huge country with the world's largest population. This dam can produce a massive amount of energy amounting to 18.2 GW of electric power, equivalent to 18 nuclear power stations. This is needed to supply sufficient energy to support their busy economy, flourishing industry and their ever growing and developing society. 

Income generator - The dam also generates very significant income for both the local community and for the nation as a whole. The project also produced many thousands of jobs during the construction process and now to maintain the dam and power plant. 

Better navigation - The river has been widened as a result of the project which makes it more navigable than ever. Ships and larger boats can now pass through to the delta providing a better and more efficient transport network for goods and people. 

The negative impacts of the Three Gorges Dam

Social

Relocation of locals - Approximately 1.3 million local people have been relocated or displaced (often forcibly without compensation) and more than a hundred towns have been submerged to enable the construction of this dam.

Perished important archeological and cultural sites - The construction of this dam destroyed approximately thousands of archaeological sites forever

Environmental

Negative environmental impact - The dam is likely to have a detrimental impact on the environment by pollution and erosion threatening the lives of countless species. Sediment build-up in the reservoir has altered or destroyed floodplains and wetlands, which provide habitation for spawning animals. Other industrial processes, such as the release of toxic substances into the water also compromise the biodiversity of the region. The disruption of the rivers natural flow dynamics due to blockage will affect the migratory paths of fish. Due to the increase of ocean vessels in the river channel, physical injuries such as collisions and noise disturbances have greatly accelerated the demise of local aquatic animals. The chinese river dolphin which is native to the Yangtze River, and the Yangtze finless porpoise have now become two of the most endangered cetaceans in the world. 

Geographical impact - Following construction of the dam the area now suffers more with landslides

Lost farmland - Thousands of acres of important farmland is now under water and the new designated farmland has much poorer soil so agricultural productivity is much lower. 

Geological risks - The dam is situated in an area prone to earthquakes which poses an increased risk to the community if the dam failed. 

Economic 

Inefficient energy allotment - the energy produced by this dam may not be used well because China has a very unproductive approach when it comes to power production and supply. 

Hard vs Soft engineering

 Hard and Soft Engineering: which is the better option?

Hard engineering: strategies involve the use of technology in order to control rivers. 

Soft engineering: adopts a less intrusive form of management, seeking to work alongside natural processes.

Hard engineering:

Dams/reservoirs

How does it work?

Water can be held up behind the dam following heavy rainfall and then released slowly to prevent flooding and for other purposes. 

Benefits

• Highly effective and very successful way of controlling flooding but also normally part of a multipurpose project which can include hydroelectricity generation and the storing of water to supply for domestic, industrial, and agricultural consumption. 
• By producing electricity, Dams also generate a long term income.
• It is environmentally much cleaner energy than electricity produced by coal and gas fired power stations and much more sustainable
• They provide recreation facilities for water sports, picnic facilities and other social activities. The bigger dams such as the Hoover Dam are tourist attractions. 
• Reservoirs store water during periods of heavy rain, reducing the risk of flooding. 

Costs/Disadvantages

• A flowing river will carry silt which backs up and is deposited behind the dam, which reduces the storage capacity and is expensive and time consuming to remove. It can lead to erosion further downstream and can change the chemical composition.
• Where water is diverted into the dam from other sources, it can affected the eco system of those rivers and those rivers and the wildlife and land around them. 
• The water held back and unable to flow like a river is more prone to become polluted if surrounded by heavy industry, such as the Three Gorges Dam project in China 
• People and habitats are removed and displaced (often forcefully) and communities are lost forever to make way for the space needed for the dam, reservoir and power stations
• They are very time consuming to construct and require access to huge amounts of raw materials such as concrete and steeL. In many poor countries prone to flooding, dam construction uses up a large amount of that countries financial resources. The Three gorges dam in China cost $25.5 billion and the Dam building projects in Pakistan are estimated to cost up to $35 million. Even the much smaller Hoover Dam project cost nearly a billion dollars in today's money. 
• The cost of some dam projects has been calculated to be higher than the long term cost of any flooding that may have occurred. 
• They are very costly to maintain
• They can pose a risk if they fail and huge amounts of water are released at a time. 

Examples: Hoover Dam, Three Gorges Dam, China

Straightening

How does it work?

By artificially straightening out where a river meanders, the river is made to follow a new much more direct and shorter route and the water clears away from the area much quicker and is prevented from pooling. 

Benefits

• This avoids building on areas (often of natural beauty) and therefore has less impact on the environment and avoids the need to resettle communities.
• The channel is easier and faster to navigate.
• Reduces the risk of flooding as water moves out of the area quickly because it doesn't travel as far

Costs/disadvantages

• Changing the course of a river is fairly expensive and time consuming to implement and maintain.
• As there is a greater volume of water being carried faster and with more energy this can lead to a greater risk of flooding or erosion downstream. 
• Removing the pooling effect of the river can have a detrimental impact on wildlife habitats by removing wetlands and marshes. Can also have a negative effect on the bio diversity and water quality. 
• Often in urban areas needing the most protection the land is not available to straighten the course of the river. 

Examples: Between 1934 and 1945 the Mississippi river was straightened reducing the length of the river by nearly 150 miles. 

Soft engineering:

Flood warnings:

How does it work?

This involves having systems in place to monitor the weather forecasts and river levels in particular areas, and warn people when floods are likely to occur. Action can then be taken by those likely to be effected, for example by sandbagging doorways, raising vulnerable items or in most severe instances removing possessions or evacuating the area. 

Benefits

• Can be implemented very quickly 
• This obviously has minimal impact on the environment and is socially sustainable. 
• The costs are significantly less than hard engineering alternatives and also cost very little to maintain. 
• They have lower education and technology requirements so they can be implemented by local people and in remote parts of poor countries. 

Costs/Disadvantages

• It does not stop the flood from happening or the damage the floodwaters cause. 
• Flood warnings are usually communicated through the internet, television and radio and some people, including the most vulnerable, may not have access or simply may not be using it at the relevant time. 
• People do not always react how they should do to warnings

Example: Tewkesbury 2007 gave people valuable time to move possessions, turn off services and take precautions. 

Flood preparation

How does it work? 

The environmental agency monitors weather forecasts and river levels, and provides information on how to prepare for a flood and what to do during, and afterwards. 

Benefits 

• Having systems in place to provide sandbags, storm gates, door guards in areas prone to flooding reduces damage.
• Relatively quick and cheap to implement, as in particular it empowers individuals to take steps rather than to rely on the authorities. Enabling people to minimise the damage caused by the floods is financially advantageous and reduces the impact of the floods on peoples lives. It also reassures people living in flood risk areas and can reduce insurance premiums and improve insurance availability. 

Costs/Disadvantages 

• It does not stop the flood from happening in the first place. 
• It could give people a false sense of security 
• It is expensive to modify homes and businesses 

Example: The environment agency and all local authorities in the UK have flood risk assessments and preparation schemes in place. 

Flood plain zoning

How does it work?

The flood risk is assessed across different parts of the floodplain and the use of the land takes this into account. Deliberate flooding is encouraged on low value land such as marshes or grassland to prevent flooding of more valuable land downstream. 

Benefits

• If nothing is built on the areas prone to flooding there is nothing to be damaged and the area will soon return to its normal state. 
• If the floodplain is not urbanised infiltration can occur more successfully, and there is less surface run off to overwhelm the rivers. 

Costs/Disadvantages 

• This can have an adverse effect on planning, preventing development where it is needed and in particular houses being built in areas where there a huge shortages. 
• It does not help areas that are already built on. 

Example: following the flooding in Lynmouth in Devon in 1952, zoning was used to identify areas around the river most at risk from flooding. 

Do Nothing

How does it work?

This involves leaving the river to do just as it wishes, which includes flooding at times and to adjust or adapt to what happens. No money is spent on new engineering methods or maintaining current ones. 

Benefits

• Financially it costs nothing directly and humans, wildlife and plants are able to adapt to the changing environment. 
• It is environmentally friendly. As long as the flooding is not a direct consequence of human activity it can be seen as the environment changing and evolving. Many of the fantastic geographical features we enjoy such as marshlands, wetlands, valleys and deltas can be as a result of flooding. 
• Material is deposited from the flood onto the floodplain making the land more fertile.

Costs/Disadvantages

• The indirect costs of the damage to property and the environment and the social effects of flooding are high. The flood will cause a lot of damage. 
• Insurance costs for those living in the area are very high or unavailable. 

Example: Parts of Africa do not have the resources to implement schemes and often are forced to do nothing or very little. 

How and why do the effects of flooding and the responses to it vary?

How and why do the effects of flooding and the responses to it vary? 

The effects of flooding vary according to their size and location. The impact tends to be more severe in poorer countries. Responses are generally more immediate in countries at further stages of development and the attempts made to reduce the effects come from within the affected area or country. In countries at lesser stages of development, attempts made to reduce the effects may be delayed and require international effort. Long term responses are likely to show similar differences as a result of variations in wealth and the ability to afford flood protection measures. 

Flooding in England (2007)

The flooding in many parts of England in June and july 2007 was the most extensive ever experienced. The depth may not have reached the record levels of 1947, but the scale of the areas affected reached a new high. 

Flooding in Hull

• Surface water flooding in hull
• Widespread disruption and damage to more than 7,000 houses and 1,300 businesses in Hull
• River Don burst its banks, flooding Sheffield and Doncaster
• Flooding in Derbyshire, Lincolnshire and Worcestershire
• Highest official rainfall total was 111mm at Fylingdales (North Yorkshire). Amateur networks recorded similar totals in the Hull area. 
• There were fears that the dam wall at the Ulley Reservoir near Rotherham would burst. 

Flooding in Tewkesbury

• Widespread disruption to the motorway and rail networks
• In the following days the River Severn and tributaries in Gloucestershire, Worcestershire, Herefordshire and Shropshire broke banks and flooded surrounding areas. 
• River Thames and its tributaries in Wiltshire, Oxfordshire, Berkshire, and Surrey flooded. 
• Flooding in Telford, and Wrekin, Staffordshire, Warwickshire and Birmingham.
• The highest recorded rainfall was 157.4mm in 48 hours in Worcestershire.

Frequency and location of flood events

Frequency and location of flood events

Flooding appears to be becoming and increasingly frequent event. In 1607 a great flood affected Devon, Somerset and South Wales. Major floods, however, were infrequent in the UK. 

In March 1947, major floods did occur, affecting many areas of southern, central and north eastern England, including York, Tewkesbury, Shrewsbury, Sheffield, Nottingham, and London, following the rapid melting of snow. 

The combined effects of storm surge and high tides contributed to the floods of January 1953 that hit the east coast, including Suffolk, Essex and Kent, when huge waves washed away sea defences and 307 people died. 

In 1968 another great flood affected counties in south west England. 

Since 1998 headlines about floods have been an almost annual occurrence. 

Major flood events 1998-2009

• April 1998 - Warwickshire, Gloustershire, Herefordshire, Worcestershire, Leicestershire, south east Wales - rivers Avon, Severn, Wye
• April 1998 - Northamptonshire, Bedfordshire and Cambridgeshire - rivers Nene, Great Ouse
• March 1999 - Malton and Norton flooded by Derwent and its tributaries
• May 2000 - Uckfield, Petworth, Robertsbridge, Horsham (sussex) - rivers Uck and Rother
• June 2000 - Calder Valley, Yorkshire and York - rivers Calder and Ouse
• August 2004 - Boscastle (Cornwall) - river Valency
• January 2005 - Carlisle - river Eden
• June 2007 - Large areas of south and east Yorkshire including Doncaster, Sheffield and Hull - rivers Don, Hull, Witham
• June 2007 - Parts of Lincolnshire including Lincoln and Louth
• July 2007 - Large areas of Gloucestershire including Upton-upon-severn, Tewkesbury, Gloucester - rivers Avon and Severn
• July 2007 - Oxfordshire including Oxford, Banbury and Witney - rivers Thames, Windrush and Cherwell 
• November 2009 - Cockermouth and the Derwent valley to Workington - rivers Derwent and Cocker

Bangladesh Case Study

Bangladesh

When?  July 20th 2004

Causes?

Human

• Urbanisation and rapid deforestation has had a negative effect on rates of interception resulting in more water reaching the rivers. 
• The building of dams in India has increased the problem of sedimentation in Bangladesh.
• The Ganges has been diverted for irrigation, increasing silt deposition
• Much of the slum housing has been constructed in the capital Dhaka's low lying areas which is more prone to flooding

Physical

• Low lying country, most of which lies on the flood plain delta of the Ganges, Brahmaputra and Meghra. Sources of the rivers are the Himalayas mountain range so extensive snowmelt adds to the discharge. 
• Is in a region with a monsoon climate resulting in cyclones, heavy rain and storm surges. 

Impacts

Social

1. 36 million people were affected and marooned or made homeless
2. Over 1000 people died as a result of drowning, disease due to having no access to clean water, and in several cases snake bites. 
3. Damage to crops by flooding and the prevention of a second sowing caused food shortages. 
4. Few people can afford insurance and many people lost everything they owned in the floods.

Economic

1. The floods caused serious damage to roads (15,000 km destroyed), bridges (over 900 were destroyed), embankments, railway lines and irrigation systems.
2. Power supplies were suspended for several days 
3. Air travel was suspended for july due to airports being flooded. 
4. Value of damage caused by floods assessed at $2.2 billion, which represented 4% of the countries total GDP. 
5. Over a million acres of crops were devastated by the flood waters.

Environmental

1. For 6 weeks after the floods, approximately 38% of the total land area was flooded. This included 800,000 hectares of agricultural land. 
2. In many places the inadequate sewerage system failed, sending foetid water flowing into the streets.
3. Many roads and railways were washed away by the flood waters
4. The floods caused extensive river bank erosion especially on embankment areas. The floods also caused soil erosion, water logging and water contamination. 

Responses

Short term

• The government and charitable organisations ,with the help of the Armed Forces, provided emergency relief which included food (mainly rice), water purification tablets, clothing, medicines, blankets and towels. 
• Medical teams worked as hard as they could to ward off the threat of disease
• Within a few days the United Nations had coordinated a disaster management team to provide additional critical emergency supplies and to carry out a damage and needs assessment. 
• Aid both in terms of supplies but also medical care was provided by individual countries. The UK donated £21 million in aid. 
• Local people created self help schemes to help rebuild their properties and communities. 

Long term

• Embankments and infrastructure repairs were carried out and sluice gates have been installed to help close channels when flood waters rise. 
• Homesteads were raised by 2 metres to help them survive the next floods.
• Farmers were given assistance including free seeds.
• Flood shelters and some early warning systems including by radio have been put in place.
• Additional financial aid mainly in the form of a loan from the world bank has been provided to assist with repairs to infrastructure, water management and education.
• Schemes to reduce deforestation are being introduced. 

Cockermouth, England Case Study

Cockermouth, England

When: 20-24th November 2009

Causes? 

Human

• Cockermouth is built on the confluence of two rivers making it susceptible to flooding after heavy rains
• The drains and sewers were inadequate and not designed to cope with high levels of rainwater
• Urbanisation of the town has created more impermeable surfaces which caused rain water to reach rivers quicker resulting in much higher discharge
• The flood damage coincided with reduced budgets meaning that flood defences were inadequately maintained

Physical

• The river Cocker/ Derwent rose by over 2.5m 
• Cockermouth is on the confluence of two rivers
• There was a lot of rainfall in early November 
• The land was saturated and the water from earlier Storms went straight into river channels 

Impacts

Social

1. Electricity cut off for over 1,200 people
2. Hundreds of local businesses were flooded
3. 18 farms were identified as being badly damaged by the floods 
4. Train stations flooded
5. Looting occurred 
6. Bridges were washed away, including some of architectural importance due to them being over 100 years old. This also meant that people had to make huge detours. 
7. A large number of people were unable to stay in their homes due to them being flooded. They tried to salvage what they could from their ruined homes. 

Economic

1. Businesses lost their stock as well as future trade in the run up to Christmas
2. 225 local businesses and shops were affected by the high water in the town centre, which in places rose to a level of 3 metres. They were also affected by the huge detours caused by damage to roads and bridges.
3. 18 farms were badly damaged by the floods.
4. The cost of the flood damage for the whole of Cumbria was at least £275 million and was many millions of pounds for Cockermouth alone. 

Environmental

1. Sewage water was mixed with the river water
2. Hundreds of thousands of tonnes of sand and gravel had been deposited on fields alongside the river Cocker
3. The floods caused significant erosion and deposition along the the course of the river Cocker. 
4. The floods also caused significant damage to roads, bridges, walkways and bridleways. 

Responses 

Short term

• Temporary train stations built where stations flooded
• The army built temporary walk ways
• Over 200 people were rescued by the emergency services including the Armed Forces, RNLI, Mountain Rescue and 50 of these people were rescued by RAF helicopter. 
• 20 schools were closed and used as a shelter by those made homeless by the flooding.
• Tesco built a temporary store to serve the local area.
• A flood recovery grants scheme was set up to help local businesses within 4 days after the floods and similar funds were made available to help local residents and farmers. 

Long term

• Commercial and residential property need extensive repair due to flood damage. By November 2010, 78 businesses had started trading again with most fully reopened by March 2011
• Many of the roads damaged by the tarmac being ripped away by flood waters and the damaged bridges were repaired and replaced. 
• The Environment agency spent £500,000 on flood protection improvements including higher defence walls, new higher embankments and floodgates. The river Cocker is also to be dredged to help it cope with higher water levels at times of heavy rain. These are to be maintained but with limited funding.