Flood Management - Soft Engineering

Soft engineering involves adapting to flood risks, and allowing natural processes to deal with the rainwater. It is a strategy that accepts the natural processes of the river and seeks to work with it to reduce the effects of folding rather than attempting to gain control of it. A conscious decision can be made to ‘do nothing’ but simply to allow natural events to happen, even if this involves the risk of flooding. In some poorer areas of the world, this is a necessary approach. In richer areas, it could mean money is set aside in years when flooding does not occur to provide relief after the event. However, there are many more positive approaches that can be adopted to reduce the risk of flooding without exerting a major force over the river and its processes.

Flood Management - Hard Engineering

 

Three Gorges Dam

The Three Gorges dam was constructed at Yichang on the River Yangtse. The capacity of the reservoir should reduce the risk of flooding downstream from a 1-in-10-year event to a 1-in-100-year event. Not only will this benefit over 15 million people living in high-risk flood areas, it will als protect over 25,000ha of farmland. The dam is already having a positive impact on flood control, navigation and power generation, but it has caused problems. The Yangtse used to carry over 500 million tonnes of silt every year. Up to 50% of this is now deposited behind the dam, which could quickly reduce the storage capacity of the reservoir. The water in the reservoir is becoming heavily polluted from shipping and waste discharged from cities. For example, Chongquig pumps in over 1 billion tonnes of untreated sewage per year. Toxic substances from factories, mines and waste tips submerged by the reservoir are also being released into the reservoir. 

Most controversially, at least 1.4 million people were forcibly moved from their homes to accommodate the dam, reservoir and power stations. These displaced people were promised compensation for their losses, plus new homes and jobs. Many have not yet received this, and newspaper articles in China have admitted that so far over $30 million of the funds set aside for has been taken by corrupt local officials.

Flood Management

Hard and Soft engineering: which is the better option?

Hard engineering strategies involve the use of technology in order to control rivers, while soft engineering, adopts a less intrusive form of management, seeking to work alongside natural processes. Hard engineering approaches tend to give immediate results and the river but are expensive. However, in the future, they may make problems worse or create unforeseen ones. Soft engineering is much cheaper and offers a more sustainable option as it does not interfere directly with the river’s flow.
 What’s  more important?

In the aftermath of the 2009 Cumbrian floods, local people were angry that more hadn’t been done to prevent them. They accused the authorities of ‘putting salmon before people’ after their earlier request to lower the river bed by 3 metres in Cockermouth had been turned down because it might harm fish stocks.
The cost of protection

Professor Samuels advises the government on managing rivers. He said ‘It is technically possible to defend places like Cockermouth against extreme events, but only by building huge walls and embankments along the river, which would cost billions and alter the character of the town. For most people, that would be unacceptable as the floods.’

Flood defence on the River Waal -http://www.bbc.co.uk/learningzone/clips/flood-defence-dyke-construction-on-the-river-waal/3253.html

River management the River Mississippi -
http://www.bbc.co.uk/learningzone/clips/river-management-the-mississippi/3078.html

Hard Engineering

Hard engineering involves building structures to defend places from floodwater. Dams and reservoirs exert a huge degree of control over a river. The natural flow of water is prevented by a dam (often a concrete barrier across the valley), water fills the area behind it and is released or held depending on circumstances such as current and expected rainfall. Dams and reservoirs are normally constructed as part of a multi-purpose project rather than with just a single aim in mind.

The Impact of Flooding and Prediction

 Areas of high risk in the UK

The map on the left shows the areas of England and Wales considered to be most at risk from flooding in the UK. It highlights the extent to which those areas are likely to flood from overflowing rivers and exceptionally high seas if there are no flood defences in place. Flooding is a naturall occurrence, which cannot always be prevented in advance. If our climate changes as many experts predict, bringing fiercer storms and wetter winters, along with a rise in sea level, the likelihood of floods will increase.

Flood prediction

The Environment Agency works out which places are at risk from flooding and issues warnings, when necessary. Three codes are
used:
·        Flood Alert
·        Flood Warning
·        Severe Flood Warning

The codes tell people whether flooding is expected and what they should do. The Environment Agency also lets people know when the risk of any further flooding has passed.

Very interesting weblink to Env Agency and also Flood Map
http://www.shoothill.com/FloodMap/- live flood warning maphttp://www.environment-agency.gov.uk/

Interesting video link -
http://www.bbc.co.uk/learningzone/clips/cities-on-flood-plains/11960.html

Flooding on the River Tay -
http://www.bbc.co.uk/learningzone/clips/river-tay-floods-in-1993/4309.html

Is flooding happening more often?
The simple answer is yes but the cause is more difficult to ascertain. From the 1960s to the 1990s, big floods were pretty rare in the UK. However, serious floods now seem to be
happening more often, as the table shows below:

 

Flooding Case Study in LEDC

Pakistan, Asia - Poor Country

Pakistan

 

 t the end of July 2010 usually heavy monsoon rains in northwest Pakistan caused rivers to flood and burst their banks. The map below shows the
huge area of Pakistan affected by flooding. The floodwater slowly moved down the Indus River towards the sea.

Continuing heavy rain hampered the rescue efforts. After visiting Pakistan, the UN Secretary General, Ban Ki-moon, said  that this disaster was worse than anything he’d ever seen. He described the floods as a slow-moving tsunami.

The effect of the floods

 At least 1600 people died

20 million Pakistanis were affected (over 10% of the population), 6 million needed food aid

Whole villages were swept away, and over 700,000 homes were damaged or destroyed

Hundreds of thousands of Pakistanis were displaced, and many suffered from malnutrition and a lack of clean water

5000 miles of roads and railways were washed away, along with 1000 bridges

160,000km2 of land were affected. That’s at least 20% of the country

About 6.5 million acres of crops were washed away in Punjab and Sindh provinces

The responses to the floods

 ·        Appeals  were immediately launched by international organisation, like the UK’s Disasters Emergency Committee – and the UN – to help Pakistanis hit by the
  floods
·         Many charities and aid agencies provided help, including the Red Crescent and Medecins Sans Frontieres
·        Pakistan’s government also tried to raise money to help the huge number of people affected
·        But there were complaints that the Pakistan government was slow to respond to the crisis, and that it struggled to cope
·        Foreign Governments donated millions of dollars, and Saudi Arabia and the USA promised $600 million in flood aid. But many people felt that the richer foreign governments didn’t do enough to help
·        The UN’s World Food Programme provided crucial food aid. But, by November 2010, they were warning that they might have cut the amount of food handed out, because of  a lack of donations from richer countries

Flooding Case Studies in MEDC

Cockermouth, UK - Rich Country (MEDC)

 

Causes: Rain 

A massive downpour of rain (31.4cm), over a 24-hour period triggered the floods that hit Cockermouth and Workington in Cumbria in November
2009

What caused all the rain?

The long downpour was caused by a lengthy flow of warm, moist air that came down from the Azores in the mid-Atlantic. This kind of airflow is common in the UK during autumn and winter, and is known as a ‘warm conveyor’. The warmer the air is, the more moisture it can hold.

What else helped to cause the Cumbrian Floods?

The ground was already saturated, so the additional rain flowed as surface run-off straight into the rivers

The steep slopes of the Cumbrian Mountains helped the water to run very rapidly into the rivers 

The rivers Derwent and Cocker were already swollen with previous rainfall

Cockermouth is at the confluence of the Derwent and Cocker (i.e. they meet there)

 The effects of the flood

Over 1300 homes were flooded and contaminated with sewage

A number of people had to be evacuated, including 50 by helicopter, when the flooding cut off Cockermouth town centre

Many businesses were flooded causing long-term difficulties for the local economy

People were told that they were unlikely to be able to move back into flood-damaged homes for at least a year. The cost of putting right the damage was an average of £28,000 per house 

Insurance companies estimated that the final cost of the flood could reach £100 million 

Four  bridges collapsed and 12 were closed because of flood damage. In Workington,  all the bridges were destroyed or so badly damaged that they were declared unsafe – cutting the town in two. People faced a huge round trip to get from one side of the town to the other, using safe bridges

One man died– PC Bill Barker

Responses to the flood

The government provided £1 million to help with the clean-up and repairs and agreed to pay for road and bridge repairs in Cumbria

The Cumbria Flood Recovery Fund was set up to help victims of the flood. It reached £1 million after just 10 days

Network Rail opened a temporary railway station in Workington     

The ‘Visit Cumbria’ website provided lists of recovery services and trades, and people who could provide emergency accommodation

Management of future floods at Cockermouth

£4.4 million pound management scheme

New flood defence walls will halt the spread of the  river

Funding from Government and local contributors

River dredged more regularly to deepen the channel 

New embankments raise the channel height to reduce the likelihood of extra floods

New floodgates at the back of houses in Waterloo street

 

Human Causes of Flooding - Climate Change and Global Warming

Global warming has been blamed fr what some claim is an increasing frequency of flooding. There is evidence that average sea temperatures have risen and this rise has been blamed for the increasing frequency and severity of tropical revolving sotrms in the Caribbean. Such storm bring heavy rainfall and storm surges along the coastlines of countries lying in their path. In spring 2005, scientist reported that average sea temperatures were 3 degrees Celsuis above normal and predicted that the 2005 hurricane season in the Caribbean and southern states of the USA would be particularly savage. This proved to be the case. notable hurricanes included Katrina, which led to the flooding of New Orleans.

It is predicted that global warming will result in reduced rainfall in some areas, but in other, such as western Europe rainfall totals might increase. higher temperatures will result in increased evaporation over the seas and oceans, leading to greater precipitation. Such an increase will inevitably cause more rivers to flood, particularly since most floodplains have become heavily urbanised over the last two centuries.

Global warming could lead to the melting of the polar ice caps. One major consequence of this would be a rise in sea level, so floodplains lying close to the present sea levels would be at risk from flooding. The major deltas of the world, such as those of the Nile, the Mississippi and the Ganges-Brahmaptura, would be at particular risk.

Reference: http://www.acegeography.com/causes-of-flooding.html