Flooding case studies

I am getting the impression that many of you are still struggling when it comes to case studies and which ones it is we need to know and so I thought that I would try and summarise each one over the next week - starting off with the rivers ones....

So, according to the revision guide we need to know about flooding in Bangladesh and Gloucestershire, hard-engineering in the Mississippi and a soft engineering case study (either the river Quaggy or river Rhine). Firstly, I thought I would start off with the flooding case studies so here goes......

BANGLADESH FLOODS 1998 

Physical causes:-

• most of the country is a huge floodplain and the deltas of the river Ganges and Brahmaputra. 70% of the land is less than 1m above sea level whilst rivers and lakes cover 10% of the land
• they experience heavy precipitation due to seasonal monsoon rains, glacier melt, storm surges and cyclones

Human causes:-

• the building of the Farraka Dam in India in 1971 is blamed for the raising of the river bed of the Hooghly River, a tributary of the Ganges. During the dry season the dam reduces the discharge of the river, thereby encouraging sedimentation on the river bed and increasing the risk of flooding
• urbanisation - recent development schemes involving the construction of networks of roads and embankments have added obstacles to the free drainage of water from the land and reduce the amount of permeable surfaces
• climate change - some people link global warming to rising sea levels. The Bangladesh floods in 1998 were notable for their long duration of 56 days. This was blamed, by some, on higher sea levels which increased the time it took for water in infiltrate on the floodplain. An increase in global temperatures was also believed to have caused the execptional high levels of precipitation experienced in the Himalayas during that same year
• deforestation - the Ganges and Brahmaputra's sources are located in Nepal and Tibet where, in recent years, their rapidly increasing populations have caused the removal of vast areas of forest to provide grazing land and a fuel source (it is estimated that 50% of the forest cover in Nepal that was present in the 1950's has been cut down). Vegetation plays a big role in the hydrology of the upland drainage basins due to the fact that it absorbs water from the ground, binds soil particles and reduces the impact of rain on the ground. Overall the forest cover slows the journey of water to the river channels and therefore reduces the risk of flooding. The removal of forests has reduced interception and increased landslides, surface runoff and soil erosion. The silt and soil which is eroded is deposited in the river channel, causing the raising of the river bed and reducing the capacity of the river. It has been estimated that soil is being lost 400 times faster in deforested areas and is responsible for raising the river bed of the Brahmaputra by 5cm a year.

Social Impacts:-

• over 1000 people were killed whilst millions were displaced
• in Assam, in the north-east, more than 1 million people lost their homes and in the Nalbari district 240 villages were submerged
• an embankment protecing Sandwip, a large coastal isalnd, was breached by the high tide and marooned 1,200 families
• 46 out of the 64 districts flooded
• livestock and crops were lost
• 7000 people had to find shelter in the Government relief camps
• transport links and infrastructure were severly damaged

Economic Impacts:-

• crops sumerged meant loss of income from agriculture
• industrial processes had to be halted due to structural damage and lack of transport for workers
• cost the country $1 billion

Environmental Impacts:-

• as the waters receded, brown fields of rotting crops, villages buried in sand and silt and wrecked roads and bridges were left behind
• risk of food shortages as millions of hectares of agricultural land was underwater
• large amounts of farmland washed away
• acute shortages of drinking water and dry food
• respiratory infections affected large numbers of people along with outbreaks of cholera and other diseases that spread easily in water
• landslides

The short term response to the floods:-

• Bangladesh Government - distibuted money and 400 tonnes of rice and provided relief supplie of freshwater, water purification tablets, sanitation services. Also appealed for national unity and calm in the wake of the disaster and the general strike which took place in response to the flooding and accusations that the government failed to get basic goods to the people affected.
• Governments of other countries - the UK sent steel bridge materials and 100,000 million tonnes of wheat. Canada provided 12,500 million tonnes of wheat and money for medicine, watertablets, house repair materials, sanitatin and rehabilitation of farming and fishing. Egypt sent money for medicines whilst Saudi Arabia sent two cargo planes with food, medicines, blankets and tents.
• The Disaster Forum (a network of aid agencies)- provided boats to rescue people and take them and their belongings to high ground. Supplied medicines to treat and prevent the spread of disease. Medecins Sans Frontieres used 6 mobile teams in boats to travel around one region in which people were literally living in the water. Supplied clean drinking water by digging and repairing wells. Monitored the health situation and set up a medical treatment centre. Distributed fodder for lifestock. Distributed food, plastic sheeting and water purification tablets. Planned a rehabilitation programme to repair and construct housing and sanitation.

The long term responses:-

• The flood action plan was created to try and reduce the severity of the damaged caused by future floods.
• Taming the Brahmaputra is being considered and so far the possible methods to do this include:
• Narrowing the channel by 4km
• Building 8000km of levee embankments
• Building wing dykes to trap sediment - at present, modelling suggests that it would cost $5 million to build one dyke (which is 8 times the cost of that to build one in the Mississippi) and a further $10 million to cover the start up costs. This is all before you consider the annual maintainence costs aswell.
• However, this would:
• Force millions out of there homes
• Distrupt fisheries
• Change agricultural patterns and irrigation patterns - with 80% of the population dependent on agriculture this would be a big problem
• As mentioned above, very costly due to the fact that all the materials would need to be imported due to the lack of resources on Bangladesh

RIVER SEVERN 2007

Physical causes:-

• weather conditions throughout the summer were far from the norm. The jet stream, which influences the path taken by the low-pressure weather systems in the north Atlantic, had followed an abnormally southerly path. This meant the usual anticyclonic weather conditions, influenced by the high pressure cell in the Azores, did not materialise
• rainfall totals May-July were highest on record since 1766 with July being the wettest July on record
• flood risk in summer is usually reduced by dry soil conditions. However, in this case there had been early summer rainfall so soils were already close to field capacity and this, accompanied with the higher than normal groundwater levels, meant there was little infiltration capacity
• torrential rain - 78mm fell over 12 hours

Human causes:-

• many housing developments were either built on floodplains or encroached on the river banks
• urbanization = increase in impermeable surfaces which reduces infiltration and thereby increases surface runoff
• removal of vegetation reduces interception store and, because there is nothing to trap the movement of sediment, raise the level of the river bed
• gutters and drainpipes, which do the equivalent of the natural processes of throughfall, stemflow and leaf drip etc, are much more efficient flows and so the water enters the channel quicker

Social Impacts:-

• 13 people died
• 2000 people had to stay in rest centres
• electricity had to be turned off which left 42,000 homes in Gloucester withotu power
• 3966 homes flooded with 1300 experiencing major loss of possessions
• 1950 people had to be rescued
• 350,000 people left without clean water

Economic Impacts:-

• Total cost = £6 billion
• 10,000 motorists stranded on the M5 with 500 people stranded at the railway
• £2.5 million to repair highway damage
• 20 schools badly damaged
• 500 businesses flooded and over 7,500 temporarily closed
• £2 million to repair community buildings
• Large increase in insurance premiums for those living near rivers

Environmental impacts:-

• flooding of water treatment plants resulted in water pollution
• loss of crops and damage to agricultural land
• much of the mand was under 3ft of water and once this disappeared it left behind muds and sands which damaged the land

Responses to the flooding:-

• rest centres set up by the County Council
• Army distributed water bottles and 23 bowser tanks were used to supply drinking water
• Gloucester fire and rescue service attened 1,800 calls in 18 hours
• RAF rescued those trapped in buildings and cars

River managment techniques implemented as a response to the floods:-

• Early warning systems improved
• River flood defences anaylsed
• Analysis was conducted of the areas prone to flooding
• Sandbags prepared for expected flash floods
• 73,00 people (additional) singed up to flood warning systems
• 8500km of flood defences inspected

So, there are the two flooding case studies - sorry alot of it is in note form but I think this is the basics of what we need to know - either later tonight or tomorrow I will try and write about hard engineering in the Mississippi and soft engineering in the River Quaggy and River Rhine.......

Dealing with the aftermath of flooding

This is slightly off topic (if you can bear the length there is a link to climate change right at the end) but I have been trying to keep ontop of some of the population and rivers stuff and so I thought I would try and write a blog post which discussed how different countries deal with the aftermath of flooding. I have also tried to explain how the La Nina oscillation caused extreme rainfall in Australia and Sri Lanka but it is rather complicated - don't fret it is no longer on the syllabus!

Over the past few weeks the news has been filled with stories about flooding across the globe. It is believed that they have all been caused by the same thing – the La Niña oscillation. This oscillation is rather complicated and scientists don’t really understand why or how it happens but I am going to try and explain some of the basics (as I understand them). La Niña occurs when the surface temperature of the water in the eastern Pacific cools and the western waters get warmer. This increase in surface temperature to the west means that the water has more energy and so heavy rainfall and storms become more frequent. The cold water from the deep depths of the ocean gradually rises upwards and collects off the west coast of South America. Strong easterly trade winds pull the cold water across the Pacific. This causes warm water and high pressures to build up along the east coast of south-east Asia and Australia where it becomes trapped which results in heavy rainfall. La Niña has varying impacts on the climate in different parts of the world. Usually the parts of the world that normally experience dry weather become drier and those with wet weather become wetter. The Atlantic and Pacific hurricane activity often increases with La Niña and the effects of severe droughts are likely in those already dry parts of the world.

Although it is believed that the recent floods in Australia and Sri Lanka were caused by the same weather system; the precipitation that fell has had very different impacts on these regions and the two different countries have taken very different approaches to deal with the aftermath of the flooding. Brazil has also experienced floods but it is unclear if this was caused by La Niña as the Met Office claim that La Niña should have made Brazil drier this year. This is an example of how scientists are still unsure about La Niña and also El Nino which has the opposite effect on the climate. The El Nino Southern Oscillation is created when the trade winds that blow along the South American coast from the south east weaken and the temperature of the sea along the South American coast begins to rise. The atmospheric pressure decreases in the eastern Pacific and rises in the western Pacific which causes the warm air and water to move to the eastern side of the Pacific where it replaces the colder water supplied by the Humboldt current. Usually this causes increased levels of precipitation for the western and southern areas of South America and, the lower ocean temperatures create exceptionally dry weather in the countries in the Indian Ocean and the western Pacific. It is unclear what causes the switch between a La Niña and an El Nino and scientists don’t really know if there is any pattern to when they switch.

In Australia the floods, so far, are believed to have claimed 35 lives but there are still some people missing. The floods forced thousands of people to abandon their homes and their belongings. The flooding was caused because the annual monsoon rains coincided with La Niña. These two different weather phenomena do not usually occur simultaneously but, as I am sure you are all aware, when they did the impact on Australia was vast. Last year Australia experienced many bush fires and droughts and the conditions required to provoke these events were created by the El Nino Southern Oscillation. This meant that the ground was extremely dry and so flash floods became a possibility if enough precipitation fell in a short time. As you are all aware, this is exactly what happened as the La Niña oscillation at the beginning of the year, which has been suggested to be the strongest one on record, created an awful lot of rain. Australia experienced its wettest December on record in Queensland with around four times the average rainfall in places and between 400mm and 1200mm (up to 4ft) of rain fell during that four-week period in coastal areas of Queensland. It is not just Queensland that has been hit by flooding. The south eastern state of Victoria has also experienced floods. The Victorian floods are estimated to have killed at least 6,000 sheep and washed away 41,000 hectares of crops, costing the agricultural sector as much as $2 billion in lost production and damaged infrastructure. The impacts of the flooding in Australia vary from the destruction of infrastructure and the loss of materialistic items to the impacts it will have on the Great Barrier Reef. Fortunately only a small percentage of people who were affected by the flooding have lost their lives but, especially in developing countries, this is often not the case. The next problem facing the Australian government is how are they going to deal with the aftermath of the flooding and ultimately who is going to pay for the massive clean-operation.

The clean-up operation is going to be a gigantic task as houses will have to be cleaned, redecorated, refurnished and have all the electrical systems replaced. Fortunately, in developed countries, most insurance companies will provide the funds for most of this. This will have to be done in every house in every one of the 80 communities that was affected by this flooding. Also other infrastructure, especially bridges and roads, will have to be repaired and the cost of this is going to huge. The backbone of the recovery effort is being provided by aid assigned by the Government, charitable donations and help from the military but this is not enough to rebuild the areas hit by the floods. To help foot the bill the Australian Government, from the 1^st July, is implementing a 12 month flood tax for all those who earn over A$50,000 and who were not affected by the floods. The new tax will charge an extra 0.5% on those earning A$50,000-A$100,000 and 1% more on those earning more than A$100,000 and this tax is expected to raise about A$1.8bn. Australia is developed country and so has the resources, and economy, to recover fairly quickly on their own but for other, less developed countries, it is a different story………….

Sri Lanka also experienced wide scale flooding over the last few months. It is believed that as many as 390,000 people have been driven from their homes and at least 3,744 houses have been destroyed, according to the country's Disaster Management Centre. Although, at present, only 37 people have been killed; in developing countries the secondary effects are often worse than the primary effects. It is believed that 400,000 children could starve as the floods have destroyed 21% of the rice crops in the country and so food shortages are an impending issue. Developing countries often have very poor sanitation and so the spread of water borne diseases, like cholera, is likely. Once the water supplies become contaminated it is very difficult to contain the spread of the disease and this is exactly what happened in Haiti and the outbreak has killed over 1000 people. In terms of the cost of repairing the damage, in Sri Lanka it is a lot lower than the cost of rebuilding the Australian states affected. The cost of rebuilding Sri Lanka is estimate to be around £315 million but the country cannot afford to foot this bill. The reason for such a difference in the cost of repair is due to the fact that the damage done in Australia was mainly to the infrastructure which is costly to rebuild. In Sri Lanka the damage to infrastructure would be minimal in comparison as there is not as much developed infrastructure in the country. However, in Sri Lanka, the human cost is going to be a lot higher. In developed countries insurance companies pay out to provide the money need for the cost of repair to houses and taxes are then used to pay for the repair work needed on infrastructure etc. In Sri Lanka this is not the case and instead they have to rely on aid from other countries. So far medical units have been sent to the area to help those who have sought shelter in crowded relief camps and the government have sent military helicopters to distribute aid and used transport aircraft to move aid from the capital, Colombo. Four camps have been set up to help flood victims and troops have been deployed to distribute food and medical supplies. India has sent a plane loaded with food supplies as well as blankets and water purification tablets. The US said it was sending aid and has supplied boats to rescue the stranded and distribute bottled water, cooking materials and tarpaulins. Reaching those in remote areas is often an issue and countries often rely on the helicopters and boats provided by countries like the US to reach those in danger as they, themselves, do not have the resources to do so.

Australia will recover a lot quicker from the flooding than Sri Lanka will. The flooding that occurred in Pakistan 6 months ago is still causing problems in the country today. Over 1000 people died in Pakistan itself and around a 100 more in neighboring Afghanistan whilst thousands lost everything. The biggest issues provoked by the floods were the spread of diarrhoea and cholera and shortages of food and clean water. Pakistan had to depend on aid from other countries in a similar way in which Sri Lanka are doing so now. The UN provided £6.5 million in aid for the relief effort and the UK provided £10 million. The US also offered aid and as well as $10 million they provided 12 temporary bridges to replace most of those that were destroyed by the floods. The worrying fact is that, 6 months on, people are still dying due to the secondary impacts created by flooding. Some blame Government inefficiency, for example, the Sindh area is in desperate need of around 500,000 blankets but so far the Government has only sent 13,000. So the question is, how long will it take Sri Lanka to recover from the flooding and how sufficient and effective is just sending monetary aid?

In terms of development Brazil is probably in between Australia and Sri Lanka. The floods, which then led to landslides, killed over 800 people in Rio de Janeiro and over 500 people are still missing. Brazil is taking a totally different approach to dealing with the aftermath of the flooding. The Government has proposed to build 8000 ‘free’ houses to replace those that were destroyed by the flooding. President Dilma Rousseff has said 6,000 of the proposed homes would be paid for by the state and federal governments and the other 2,000 would be donated by a consortium of construction companies. The houses would be given to families living in shelters after their homes were destroyed and to those who were being removed from areas considered at risk of further flooding and landslides. It is planned that the proposed homes will be built on public land and the construction cost subsidised by the federal government and private companies, with the Rio state government then paying the monthly purchase instalments on behalf of poor families who move in. As well as trying to deal the aftermath of flooding, the Brazilian Government are also trying to implement measures to reduce the impacts if such an event was to occur again. The Government are directing funds to projects which involve mapping out areas that were prone to flooding and landslides and clamping down on unauthorised building in danger zones. Federal money is also being made available to rebuild roads and bridges and fund drainage and hillside stabilisation projects. The hope is that these new measures will reduce the impacts that future floods and landslides will have on the area and the people of Brazil.

These three countries have taken very different approaches to dealing with the aftermath of flooding but is there a right or wrong way to deal with the impacts of flooding? I think that it depends on the area as less developed countries could not implement a temporary tax to foot the bill of the clean-up. Developing countries have to rely on aid to recover after a disaster instead but often monetary aid alone is not enough. Advisors and medics are often needed more than just money to help ensure that the aid actually reaches the people that need it. I think the approach that Brazil has taken to floods is quite sustainable as not only are they trying to deal with the present situation but also prevent a similar one from occurring in the near future. Poor sanitation and unstable buildings in the favelas in areas like Rio de Janeiro escalate the impacts of flooding as they make landslides more likely and the spread of diseases more probable and by making building regulations stricter hopefully the conditions in the favelas can be improved and therefore the secondary effects of future floods less damaging.

Now I am going to try and link flooding to the current module. A recent report that investigated the flooding that the UK experienced during 2000, which damaged 10,000 houses and caused £1.3 billion worth of insurance loss, has blamed climate change for the flooding. This is the first time that anyone has linked a single weather event to climate change since Al Gore implied that human induced climate change caused Hurricane Katrina. Two reports that were released this week have suggested that the increase in greenhouse gas emissions, which has caused the average global temperatures to rise, has significantly increased the risk of flooding as warm air holds more moisture than cold air. Record high sea temperatures are believed to be the reason for La Nina being so strong this year and having such a devastating effect. It is believed that as we increase our greenhouse gas emissions the probability of severe floods occurring across the global will increase. The method used to come to this conclusion was to compare two climate models which were based on two different scenarios. The first one was classed as a realistic scenario and was based on the greenhouse gases that were present in the atmosphere during 2000 whilst the other one was based on a world where humans had not created and emitted any greenhouse gases. The conclusion of the report that used this method was that human greenhouse gas emissions "significantly increased" the likelihood of the 2000 floods and, they claimed, with a 66 per cent confidence level, that emissions nearly doubled the risk of the 2000 floods. http://www.newscientist.com/article/dn20141-blame-human-emissions-for-british-floods.html

 The other report, which was carried out between Canada and the UK, studied the increase in the frequency of extreme precipitation events that occurred in the Northern Hemisphere between 1950 and 2000. They concluded that, although there have been some variations, extreme rainfall events have become more common and the only explanation of this trend is the slow steady increase in temperatures provoked by greenhouse gas emissions. http://www.bbc.co.uk/news/science-environment-12484314

Both of these reports suggest that the possibility of floods, like those experienced in Australia, Sri Lanka and Brazil this year, occurring has significantly increased. This means that countries are going to have to be more prepared and have more efficient ways of dealing with the aftermath of flooding. So, is this really a great time for the government to announce that they are cutting the funds for flood denfences by 8%? http://www.bbc.co.uk/news/uk-politics-12402284