Flood Management Strategies Flashcards
(40 cards)
1
Q
What does hard engineering involve and disadvantages
A
- man-made structures that reduce flooding
- expensive to build and maintain, and need technical skill. Poorer countries often can’t afford these flood offences
- floods happened less often, but they can be more hazardous if they do happen e.g. if a dam breaks then a huge amount of water will rapidly flood the land
- natural processes are disrupted e.g. crops don’t get fertile silt from river sediment during low-level flooding
- some people think they’re ugly
2
Q
How do dams work
A
- huge walls built across rivers
- a Reservoir is formed behind the dam
- floodwaters caught by the dam, which prevents flooding downstream
- the water is released as a steady flow throughout the year
3
Q
Benefits of the dam
A
- turbines are often built into the dam, which generates electricity
- steady water release allows irrigation of land below the dam throughout the year
- people can use the reservoir for recreational activities, e.g. sailing
4
Q
Disadvantages of the dam
A
- theyre Very expensive
- land is flooded when the reservoir is created. This often destroys farmland and forces people to move elsewhere
- there may affect wildlife e.g. They can prevent salmon migrating upstream to breeding ground
- the trap sediment normally carried in rivers. this can cause the dam to fail. it can also cause increased Erosion downstream, as there is less protective sediment being deposited
5
Q
How does channel straightening work
A
- where meanders are removed by building artificial cut-throughs
- this makes the water flow faster, which reduces flooding because water drains downstream more quickly and doesn’t build up to a point where the river channel can’t contain it any more
6
Q
Benefits of channel straightening
A
- it takes less time to navigate the river because it has been made shorter
7
Q
Disadvantages of channel straightening
A
- flooding may happen downstream instead, as floodwater is carried their faster
- more erosion occurs downstream because the river flows faster
- altering river channels disturbs wildlife habitats
8
Q
How do you levees work
A
- embankment built along rivers
- the river can hold more water without overflowing and so floods less often
9
Q
Benefits of levees
A
They allow the floodplain to be built upon
10
Q
Disadvantages of levees
A
- expensive quite
- risk of severe flooding if breached
11
Q
How do diversion spillways work and benefits
A
- channels that take water elsewhere if the water level in the river is too high
- water is normally diverted around an important area or to another river
- they prevent flooding because with the discharge is reduced
- often have gate that can be opened, so the release of water can be controlled
12
Q
How do diversion spillways work and benefits
A
- channels that take water elsewhere if the water level in the river is too high
- water is normally diverted around an important area or to another river
- they prevent flooding because with the discharge is reduced
- often have gate that can be opened, so the release of water can be controlled
13
Q
What are soft engineering and their benefits
A
- use knowledge of whole river basin and its processes, To work with nature
- cheaper to maintain Which is important to poor countries
- flooding is more predictable, reducing the risk of an unexpected disaster
- they can improve opportunities for recreation such as fishing
- some people think they’re more attractive
14
Q
How does land-use management work
A
- planning restrictions present buildings or roads being constructed on the floodplain
- use of the floodplain is restricted to things like playing fields, allotments or parks
- more water can infiltrate so it’s less surface run-off, which reduces discharge and flooding
15
Q
Benefits of land-use management
A
- lonely buildings or roads in the floodplain to be damaged, so the impact of any flooding is reduced
- provides recreational opportunities e.g. football fields
16
Q
Disadvantages of land-use management
A
- restricts development. This is especially a problem where there’s a shortage of housing
- can’t be used in areas are already urbanised
17
Q
How does wetland and riverbank conservation work
A
- still floodwater and also slow it down
- this reduces flooding downstream
- conserving all re-establishing wetlands is natural protection from flooding
- planting trees and shrubs along the river bank increases interception and lack time, And reduces discharge. This can also decrease flooding
18
Q
Benefits of wet land and riverbank conservation
A
- vegetation protect the surface soil from erosion
- the vegetation provides habitats for wildlife
19
Q
Disadvantages of wetland and riverbank conservation
A
- less land is available for farming
20
Q
How does the river restoration work
A
- involves making the river more natural e.g. by removing man-made levees
- the floodplain can then flood naturally
- as the water spreads out over the floodplain Rivers discharges reduced, which reduces flooding downstream
21
Q
Benefits of River restoration
A
- Little maintenance is needed, as the rivers left in its natural state
- the river provides a better habitat for wildlife
22
Q
Disadvantages of river restoration
A
- local flood can increase, Especially if nothing is done to prevent major flooding
23
Q
How does alteration of urban surfaces work
A
- building porous pavement or soakways increases infiltration, which reduces rapid surface run-off to the river channel
- this increases last time, which reduces discharge and flooding
24
Q
Benefits of alteration of urban surfaces
A
- any pollutants in the water are filtered out by the soil before the water reaches the channel
25
Disadvantages of alteration 11 surfaces
- expensive
26
Scheme for reducing impact of flooding (soft engineering)
how does it work
- the environment agency monitors weather forecasts, rainfall and river discharge
- they warn people about possible floods to TV, radio, newspapers and the Internet
- this means people can evacuate before the Flood happens, saving lives
- people can also move possessions and use sandbags to help reduce the damage
27
Disadvantages of scheme to reduce impact flooding
- some people might not be able to access the communication network
- Flash floods may happen to fast for warnings
- people may ignore warnings if they were in the past
28
Disadvantages of scheme to reduce impact flooding
- some people might not be able to access the communication network
- Flash floods may happen to fast for warnings
- people may ignore warnings if they were in the past
29
Why soft engineering more sustainable and hard engineering
- hard engineering is often expensive and disrupts natural processes
- soft engineering tends to be cheaper and requires much less time and money to maintain
- soft engineering is designed to integrate with the natural environment and create areas like wetlands, which are important habitats for wildlife
- soft engineering has a low economic cost and environmental impact
30
Hard engineering on the Yangtze River to control flooding
- the Yangtze flows through China. At 6380 km long, it's the third longest river in the world.
- seasonal flooding is coming around the Yangtze – China has a rainy season that lasts from about June until August and the huge increase in river discharge during this time often causes flooding. Flooding causes huge problems as there is lots of farmland and loads of major cities Next to the river, e.g. Wuhan and Nanjing
- five major floods have happened over the last century– In 1931, 1935, 1949, 1954 in 1998
- the flood of 1954 covered 193,000 kilometres squared of land and killed 32,169 people. Over 18 million people had to move. It covered the city of Wuhan for Over three months
- the flood in 1998 killed around 3000 people and made 14 million people homeless
- flood protection is mostly down to hard engineering differences
31
Hard engineering on the Yangtze River to control flooding
- the Yangtze flows through China. At 6380 km long, it's the third longest river in the world.
- seasonal flooding is coming around the Yangtze – China has a rainy season that lasts from about June until August and the huge increase in river discharge during this time often causes flooding. Flooding causes huge problems as there is lots of farmland and loads of major cities Next to the river, e.g. Wuhan and Nanjing
- five major floods have happened over the last century– In 1931, 1935, 1949, 1954 in 1998
- the flood of 1954 covered 193,000 kilometres squared of land and killed 32,169 people. Over 18 million people had to move. It covered the city of Wuhan for Over three months
- the flood in 1998 killed around 3000 people and made 14 million people homeless
- flood protection is mostly done through hard engineering defences
32
Defences on the Yangtze to control flooding
- many dams that reduce flooding (46 are planned or under construction at the moment) this biggest of these is the three gorges dam:
- work began on the 101 m high three gorges dam in 1994
- a Reservoir is building up behind the dam. The reservoir catches any floodwater, which can then be slowly released overtime. The reservoir can store around 22 km³ of floodwater
- it's also the largest hydroelectric power station in the world. The flow of water turns 26 turbines built into the dam
- locks have been built alongside the down so ships can get past it
- there are also many levees along the river. E.g. there are 3600 km of levees along the middle and lower parts of the River
33
Positive effects of the three gorges dam
- it's thought that the down has reduced major flooding from once every 10 years to once every hundred years
- the turbines in the jam produced a lot of electricity – capacity is likely to reach 22.5 GW (enough to supply about 3% of China's demand which is loads)
- a reduction in flooding has made a much safer to navigate up The river. River shipping has also increased as big as ships can now travel up the river because the reservoir is deeper than the old river
34
Negative effects of there levees along the Yangtze
- in the 1998 floods many levees broke, which contributed to devastating flooding
- after this, many levees were reinforced. They were effective at reducing flooding in the 2002 flats
35
Negative effects of the three gorges dam
- people have had to relocate as the water level in the reservoir has risen. It's thought that between 1.3 and 2 million people in total have to relocate by the time it's full - 13 cities and 1352 villages will be submerged
- the reservoir will also flat farmland, 657 factories, and 1300 site of cultural and historic interest. Four example as the water rises the temple of Zhang Fei will be submerged
- a huge amount of sediment is normally carried down the river. The dam will trap the settlement, which could lead to failure of the dam and cause catastrophic flooding
- could destroy habitats and endanger species. Few are than 100 baiji dolphins are left in the river, and the dam could reduce their food supply
- it doesn't protect everyone –rising water levels in the reservoir with increased flooding along the tributary is that lead onto it
36
Soft engineering in Abingdon to control flooding
- the town in south-east England, was built in the floodplains of the river Thames and River Ock
- 1500 properties in Abingdon have a 1% chance of flooding in a given year
- Abingdon has had regular floods over the years – 47, 68, 77, 79, 92 2000 and 2007
- intense storms in July 2007 cause particularly bad flash floods. River Thames and Ock burst their banks, flooding 660 properties in Abingdon. Increase surface run-off in built up areas made the flooding even worse
- hard engineering defences have been considered by having rejected the various reasons. E.g. a diversion spill way to transport floodwater south of Abingdon was too expensive, and flood barriers to protect properties along the ock would increase flood risk downstream. What protection is mostly down through soft engineering defences
37
Defences for soft engineering Abingdon
- land-use management
- flood warnings
- soakaways
38
Defences for soft engineering Abingdon
- land-use management
- flood warnings
- soakaways
39
Explain the differences in Abingdon
- Gravel soak aways have been built along the A34 Road
- Low value land is allowed to flood, e.g. Tilsley Park sportsground is being considered as an additional flood storage area
- there are planning restrictions on new housing developments built Ock floodplain, stating they must have improved drainage systems
- Tesco were forced to revise recent extension plans– they had to add drainage improvements such as soakaways and permeable tarmac
- the environment agency's local flood warning plan warns specific areas at risk and provide a 24 hour flood line
- improvements have been made to riparian buffers along smaller rivers. Planting trees reduces the volume of water reaching the Thames and ock rivers where the flood problem is greater
- local voluntary Flood wardens communicate advice and warnings
- there's detailed advice on the Internet about reducing flood damage
- there are restrictions on land use e.g. planning permission was refused for buildings on the Thames floodplain
40
How does software engineering reduced damage and flood still happen
- it's difficult to measure the success of flood defences because it's hard to figure out if any reduction in flooding was because of the success of new defences, or because the weather conditions were less severe
- several flood warnings were issued by environment agency in early 2008
- the Ock floodplain, which has developments on, didn't get flooded. the Thames floodplain did get flooded but it's largely clear of development, due to land use management and planning restrictions
- the 2008 floods less damage in previous years, with a minimal cost, little destruction to the community services, no life loss and only few injuries. However, flooding does still happen in Abingdon.
