Managing Floods

Effects of flooding

• What are the effects of flooding?

• Why do we need to manage rivers?

Managing floods

• There are two ways of managing floods to reduce their impact

• Soft engineering and hard engineering (same as with coasts)

• It is a balance of how valuable the land is, how many people will be affected, how costly the management scheme is, and how effective + sustainable the management scheme will be

River management: Hard + Soft Engineering

Hard Engineering Soft Engineering

Dams Washlands

Embankments Land-use zoning

Flood Walls Afforestation

Straightening and deepening the river

Warning systems

Storage areas

Now highlight, in different colours,

the advantages and disadvantages

of each scheme

Hard Engineering

These are traditional methods of stopping floods and require complicated engineering.

The Environment Agency has three options available: 1. build flood defences like dams, embankments and flood walls2. straighten and deepen the river and cut off meanders3. make storage areas for extra water.

DamsThese trap and store water so reduce surface runoff as water is realeased in a controlled way. The land upstream of the dam is flooded, this can change ecosystems and mean that local residents may have to move out of the area.  The reservoir lake can be used for recreation e.g. fishing Dams trap sediment behind them that would normally flow downstream. This can cause problems where farmers rely on silt providing fertile soil after flood events e.g. The River Nile Dams are very expensive but effective.

EmbankmentsThese are raised banks along the river, they effectively make the river deeper so it can hold more water before it floods. They are very expensive and do not last long (unsustainable).  Rivers can now flood without causing much damage.

Embankments are also built near settlements with washlands between the embankments and the river. 

Slide 4

Flood WallsFlood walls are built around settlements and important factories or roads. They're quite expensive and don't look very natural. These are very effective at stopping flooding. Flood walls are also used in places where there area lot of people living.

Straightening and deepening the riverThis is when the river is made straighter to make the river flow and channel flow faster so there is less chance of river flooding.

• It keeps the water levels to a minimum so it is less likely to flood.

• We can use it to make high levels of electricity.• It is very expensive to dig out and straighten the whole river,

especially if it is a very long river.• The result is often not natural looking.

Slide 6

Storage AreasWater can be pumped out of the river and stored in temporary lakes. Then it is pumped back in after the water in the river has gone down a bit.  Effective but we do need to have a large area of free land that isn't used, so that you can flood it.  

Soft Engineering

Soft engineering techniques work with the river and use natural processes.

WashlandsThese are parts of the floodplain that are allowed to flood.They can't be built on. They're usually used for sports pitches or nature reserves.

Land-use zoning    This is where the land has different building controls depending on how far from the river the buildings lie. The land next to the river is un-used land and as the distance from the river increases so does the quality and the value of land rises. Important factories, schools, and most homes should be away from the river.

Afforestation• Afforestation is the deliberate and planned planting of

various greenery (more specifically trees).    

• By doing this you can increase interception and prevent the ground from becoming saturated with water.

• However, doing this takes up a lot of room and cannot prevent serious flooding.   

 

Warning systemsWarnings are issued by the Environment Agency so that local people can put sand bags by their homes, take furniture upstairs, or even evacuate the area. People do not always listen to warning systems.

Warnings are given on tv, radio and the internet.

Slide 13

River flood example

• Example video of the Mozambique floods

• If you want that higher grade, take notes….it is your case study after all

Geog. GCSE

• P84-85

• Read through the information on the choices of management schemes

• You need two different colours of paper. On one piece, make notes on the River Derwent – the hard and soft engineering here. On the other colour, make notes on how the River Limpopo/Zambesi in Mozambique is managed.

• This has now created a revision sheet for you.

Comparing Flood control in MEDC's and LEDCs

MEDC - North Yorkshire, River Derwent • MEDC river = has money to

build defences (e.g. embankments, sluice gates,, washlands, land-use zoning) 

 • Since the flood, £7.5 million has

been spent on protecting towns  • Sluice gates upstream can hold

back water and let it out in a controlled way.

 

LEDC – Mozambique, Limpopo / Zambezi River • LEDC river = does not have the

money to build defences •     Money has been given to

Mozambique by other countries to help recover in the short term

• Cannot afford to have flood defences / prediction

Homework over holidays• Make sure you have caught up on everything.• Rivers + Coasts are now finished• You need to make sure you have got your case studies

completed, that you understand the keywords, that you know + can explain landforms/changes in coasts+rivers, and flood hydrographs

• Make a log/journal over the holiday to show what work you have done (e.g. 17th Feb, completed Mozambique case study).

• Please start using the blog. It is not there just for fun, it is your reference point. Every lesson is on there plus links to the exam board. There is a checklist of all you should know.

Managing Floods• Describe the flood defences in the photograph (1)• Explain how these defences protect against river flooding (2)

Hard and Soft Engineering

• Use the words below to complete this paragraph.

• Hard engineering techniques are that are imposed on

the river. They try to the river. Examples of hard engineering are and . Soft engineering started to be used in the 1990s. Soft engineering methods work with the river and use processes. Examples include and .

dams structures naturalafforestation

flood walls land-use zoning control

Exam Q: Responses to flooding

1. Evaluate two methods of protecting against the effects of river flooding. (4)

For 4 marks, you need to name 2 different methods and give 2 explanations. Evaluate means give the pros + cons.

– Dams• Positive, e.g. effective, control water flow• Negative, e.g. expensive, ugly

– Warning systems• Positive, e.g. sustainable, cheap, warn people to prepare• Negative, e.g. does not stop flood, may be ignored, needs

technology

Exam Q practice

2. Explain why flood defences are more effective in MEDCs than LEDCs? (4)

For 4 marks, you need to make 2 basic points and develop these with 2 explanations.

– E.g.– Countries like Mozambique have low GDP (less money) SO

they cannot afford to have flood defences.– LEDCs have to prioritise in developing basic services like

hospitals and schools INSTEAD of flood protection.– MEDCs often have BETTER prepared emergency services

and flood plans.– MEDCs have strict planning controls that prevent developers

building on high risk areas WHEREAS these controls are not effective in many LEDCs.

Foundation exam paper (so highest grade = C)

Marked out of 25.

C = 17+

D = 14+

E = 11+

F = 8+

G = 4+

Exam question feedback

Exam question feedback

River Terminology Test

• You are going to be shown 10 words.

• For each one, write the correct definition.

1. Abrasion

2. Afforestation

3. Delta

4. Floodplain

5. Groundwater flow

6. Impermeable

7. Infiltration

8. Interception

9. Transpiration

10. River basin

1. Abrasion

The scratching and scraping of the river bed and banks by the stones and sand in the river

2. Afforestation

The replanting of trees

3. Delta

A flat area at the mouth of a river made of sediment deposited by the river

4. Floodplain

Flat land around a river that gets flooded when the river overflows

5. Groundwater flow

The flow of water through underground rock

6. Impermeable

Doesn’t let water through e.g. tarmac

7. Infiltration

The soaking of water into the ground

8. Interception

The capture of rainwater by leaves

9. Transpiration

The evaporation of water from leaves

10. River basin

The area drained by a river, the edge of which is marked by its watershed

Knowledge check

• Update your checklist sheet in your book

• Make a note of the areas you feel you still need to learn more about (e.g. I’m a bit unsure about the hydrological cycle)