Flooding and flood prevention.

Question 1

What are the 4 human causes of flooding?

Answer 1

1. If vegetation has been removed, then there is less interception and water will move to the river more quickly.
2. If there is a town on a floodplain, storm drains will allow water to move into the river at a greater speed and so make flooding more likely.
3. Ploughing up and down slopes rather than around them channels the rainwater to the river faster.
4. Dams may burst, which will cause excess water in river channels and flooding of large areas.

Question 2

What are the 4 physical causes of flooding?

Answer 2

1. If there are large amounts of rain day after day, the water will saturate the ground and flow more quickly into the river.
2. During a cloudburst in a thunderstorm, the rain droplets are so large and fall so quickly that there is no time for the water to sink into the ground. Water runs very quickly into the river and causes flooding.
3. If there is a sudden rise in temperature, a rapid thaw can happen. Rivers are unable to cope with the amount of water and flood.
4. Impermeable rocks mean that rainwater cannot soak into the rocks and it therefore flows more quickly to the river either through the soil or over the surface.

Question 3

What were the effects of river flooding in Kenya in 2007? (3)

Answer 3

1. The River Tana burst its banks.
2. Much of the town of Garissa was under water, with houses near the river submerged.
3. The flood destroyed bridges and made roads impassable, meaning aid drops by plane were the only way to deliver food to the starving population.

Question 4

What were the effects of river flooding in Bolivia in 2007? (5)

Answer 4

1. Many rivers burst the banks.
2. 340,000 people were estimated to have been affected.
3. About 100,000 people were left homeless.
4. Roads in Santa Cruz and Beni were blocked by mudslides.
5. At least 19 people died as a result of flooding of the Rio Grande, a tributary of the Amazon.

Question 5

What were the effects of river flooding in India in 2008? (5)

Answer 5

1. The Kosi river burst its banks.
2. 1,600 villages were affected.
3. Thousands of people were stranded on rooftops and trees or marooned on thin strips of dry land.
4. 55 people were killed.
5. The road linking Saharia village to the rest of the hard hit Saharsa district was completely washed away.

Question 6

In what 4 main ways could the effects of floods be prevented and predicted?

Answer 6

1. Education.
2. Forecasting.
3. Building design.
4. Planning.`

Question 7

How could the effects of floods be predicted and prevented through education? (2)

Answer 7

1. Governments give advice to the general public via the internet. The advice includes information on how to protect your house.
2. On the Environment Agency website there is information on the likelihood of a flood. This will be identified through a system of warning codes: flood watch, flood warning, severe flood warning and all clear. These warning codes give people information on what to expect and how to react. In this way the government is helping to prevent the effect of floods by providing an effective warning system.

Question 8

How could the effects of floods be predicted and prevented through forecasting? (2)

Answer 8

1. The Met Office forecasts the likelihood of a flood. The information gets to householders through weather forecasts and news broadcasts on the TV and radio. It is also on their website.
2. If there is a likelihood of flooding, the Met Office advises householders to be proactive and either ring a flood hotline number or go to the Environment Agency’s website to check the likelihood of a flood in their area.

Question 9

How could the effects of floods be predicted and prevented through building design? (7)

Answer 9

1. It can cost between £3,000 and £10,000 to protect a house from flooding. Some of the techniques are:
2. Moving electricity sockets higher up the walls.
3. Replacing doors with ones that are lightweight and can be moved upstairs if necessary.
4. Concrete floors instead of wooden ones so that they do not rot if they are wet.
5. Using yacht varnish on wooden skirting boards to protect them from water.
6. Waterproof MDF can also be used instead of wood as a door frame.
7. Buildings on stilts.

Question 10

How could the effects of floods be predicted and prevented through planning? (3)

Answer 10

1. Before houses can be built, the local authority has to give planning permission. This is not granted in flood risk areas unless a flood risk assessment has been carried out.
2. From 2010, the law requires all new housing in flood risk areas to be flood resistant or resilient.
3. The Department for Environment, Food and Rural Affairs has the responsibility for deciding which areas are going to be defended against the risk of flooding. The Environment Agency then organises for the defences to be built and maintained. The Department for Environment, Food and Rural Affairs then provides the money for most of the work that is completed.

Question 11

What are the 5 main hard engineering techniques used to prevent flooding?

Answer 11

1. Flood relief channel.
2. Embankments.
   3, Channelisation.
3. Flood walls.
4. Storage areas.

Question 12

Define: Flood relief channel.

Answer 12

The channel course of the river can also be altered, diverting flood waters away from settlements.

Question 13

What are the 4 main advantages of flood relief channels?

Answer 13

1. No disruption is caused to residents next to the original course of the river.
2. Makes the people who live close to the main river safer as the flood water is diverted into the relief channel.
3. Can be used for water sports.
4. Very effective, should last for many years.

Question 14

What are the 3 main disadvantages of flood relief channels?

Answer 14

1. Extremely expensive.
2. Requires a large amount of land
3. Land might be difficult to purchase, particularly if it is productive farmland.

Question 15

Define: Embankments.

Answer 15

Raised banks along the river.

Question 16

What are the 3 main advantages of embankments?

Answer 16

1. Can be used as pedestrian paths beside the river.
2. Earth embankments provide habitats for plants and animals.
3. Concrete embankments are effective at stopping bank erosion.

Question 17

What are the 2 main disadvantages of embankments?

Answer 17

1. Often not built high enough.

2. Concrete embankments are ugly and spoil the view.

Question 18

Define: Channelisation.

Answer 18

River channel may be widened or deepened allowing it to carry more water; may be straightened so that water can travel faster along the course.

Question 19

What are the 2 main advantages of channelisation?

Answer 19

1. Effectively protects the immediate area because water is moved away quickly.
2. It is long lasting.

Question 20

What are the 2 main disadvantages of channelisation?

Answer 20

1. Altering the river channel may lead to a greater risk of flooding downstream as the water is carried there faster.
2. Unnatural and visually intrusive.

Question 21

Define: Flood walls.

Answer 21

Vertical barriers usually made from prefabricated concrete.

Question 22

What are the 2 main advantages of flood walls?

Answer 22

1. Can be used in areas where space is limited.

2. Easily and quickly erected in pre-constructed sections.

Question 23

What is the main disadvantage of flood walls?

Answer 23

They have to be assembled very well so that water doesn’t get through the joints.

Question 24

Define: Dams.

Answer 24

Often built along the course of the river in order to control the amount of discharge; water is held back by the dam and released in a controlled way.

Question 25

What is the main advantage of dams?

Answer 25

The water that is stored in a reservoir behind the dam can be used to generate hydroelectric power or for recreation purposes.

Question 26

What are the 3 main disadvantages of dams?

Answer 26

1. Sediment is often trapped behind the wall of the dam, leading to erosion further downstream.
2. Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.
3. Can be expensive to build.

Question 27

Define: Storage areas.

Answer 27

Large depression close to the river that will fill with water if the river overflows and therefore protects the surrounding land.

Question 28

What are the 2 main advantages of storage areas?

Answer 28

1. Do not damage the environment.

2. Natural looking.

Question 29

What are 2 main disadvantages of storage areas?

Answer 29

1. Need a large area of land that is not being used.

2. Only come into use when the river has flooded.

Question 30

What are the 4 main soft engineering techniques used to prevent flooding?

Answer 30

1. Floodplain zoning.
2. Washlands.
3. Warning systems.
4. Afforestation.

Question 31

Define: Floodplain zoning.

Answer 31

Local authorities and the national government introduce policies to control urban development close to or on the floodplain.

Question 32

What are the 3 main advantages of floodplain zoning?

Answer 32

1. Cheap.
2. Sustainable because it reduces the impact of flooding and building damage is limited.
3. Because the floodplain hasn’t been built on, surface run-off is less likely to cause flooding.

Question 33

What are the 2 main disadvantages of floodplain zoning?

Answer 33

1. Resistance to restricting developments in areas where there is a housing shortage.
2. Enforcing planning regulations and controls may be harder in LICs.

Question 34

Define: Washlands.

Answer 34

The river is allowed to flood naturally in wasteland areas, to prevent flooding in other areas.

Question 35

What are the 3 main advantages of washlands?

Answer 35

1. Cost-effective as nothing is built.
2. Provides potential wetlands for birds and plants.
3. The deposited silt may enrich the soil, turning the area into agricultural land.

Question 36

What are the 2 main disadvantages of washlands?

Answer 36

1. Large areas of land are taken over and cannot be built on.
2. Productive land can be turned into marshland.

Question 37

Define: Warning systems.

Answer 37

A network of sirens that give people early warning of possible flooding.

Question 38

What are the 3 main advantages of warning systems?

Answer 38

1. Cheap.
2. Electronic communication is a very effective way of informing people.
3. With warning, people can move valuable belongings to a safer place.

Question 39

What are the 2 main disadvantages of warning systems?

Answer 39

1. Sirens can be vandalised.

2. Might not be enough time for residents to prepare.

Question 40

Define: Afforestation.

Answer 40

Trees are planted in the catchment area of the river to intercept the rainfall and slow down he flow of water to the river.

Question 41

What are the 4 main advantages of afforestation?

Answer 41

1. Relatively low cost option.
2. Improves the quality of the environment.
3. Soil erosion is avoided as trees prevent rapid run-off after heavy rainfall.
4. Very sustainable.

Question 42

What are the 3 main disadvantages of afforestation?

Answer 42

1. It is often conifers that are planted, which can make the soil acidic.
2. Dense tree plantations spoil the natural look of the landscape.
3. Increases fire risks because of leisure activities in the forest.