Learning Objectives: 1)To compare the advantages and disadvantages of river defence techniques2)To consolidate our knowledge of river landscapes, river processes and river flooding

• Hard engineering is a method of river flood management which involves major construction work

• Soft engineering is a method of river flood management which works or attempts to work with natural river processes. It does not tend to involve major construction work e.g. Floodplain zoning

HARD ENGINEERING

• These are structures built by engineers, with the help of geographers and hydrologists.

• They are expensive and often not an option in LICs.• They often have a negative impact on the environment and

can even cause more flooding further down the river’s course.

• Use a full page and write the following headings along the top of the page:

• Method Description Comment

• Write notes on each technique as we go through the following slides.

Flood banks These are raised 1) Can be used as a path 1) The banks are

 

banks along the river, so it can hold more water. for pedestrians beside often not built

    the river. high enough

    2) Concrete embankments 2) Concrete

    are effective at stopping embankments

    bank erosion. are ugly and

    3) Earth embankments spoil the view.

    provide habitat for  

    plants and animals.  

Channelisation(straightening and deepening of the river)

The river channel may 1) Effectively protects 1) Altering the

  be widened and immediate area because river channel may

  deepened allowing it water is moved away lead to greater

  to carry more water. Aquickly. risk of flooding

  river channel may be 2) Long lasting downstream, as

  straightened so that   the water is

  water can travel faster   carried there

  along the course   faster.

      2) Unnatural and

      visually intrusive.

Los Angeles channelisation

Flood relief The channel course 1) Makes the people who 1) They require a

channels of the river can be live close to the main large amount of

  altered, diverting river safer as the flood land which might

  floodwaters away water is diverted into be difficult to

  from settlements. the relief channel. purchase

    2) Can be used for waterparticularly if it is

    sports. productive farmland.

      2) Extremely

      expensive.

Construction of a flood relief channel

Dams and reservoirs Dams are often built 1) Water is usually stored 1) Building a dam is

  along the course of a in a reservoir behind the very expensive.

  river in order to control dam. This water can then 2) Sediment is often

  the amount of discharge. be used to generate trapped behind the

  Water is held back by the hydroelectric power or wall of the dam,

  dam and is released in a for recreation purposes. leading to erosion

  controlled way.   further downstream.

      3) Settlements and

      agricultural land may

      be lost when the river

      valley is flooded to

      form a reservoir.

The Three Gorges Dam in China

• Use the resource sheet to complete a fact file on this example of a hard engineering scheme. Write your fact file around the map of China.

• Include:• Its main features,• Why it was built?• The impact : social, economic, environmental.• Extension work – How to get the A/A*• Use the booklet to add more detail to your case study:• 1. The history of flood events on the Yangtze (table 2),• 2. Why can the 3 gorges be described as a multi-purpose scheme?• 3. What does displacement mean and how have people been re-settled?• 4. What have the impacts on the Yangtze ecosystems been like?• 5. Add the detail from figure 1 to your map.• 6. What hazards has the dam created? • Do you think it should have been built? Do the benefits outweigh the costs?

Flood walls   

A vertical barrier usuallymade from prefabricatedconcrete. 

1) Can be used in areas where space is limited.2) Easily and quickly erectedin pre-constructed sections.

1) They have to beassembled very wellso that water doesn'tget through joints.

Flood wall on the River Moskva, in Moscow

Storage areas     

A large depression close to the river that will fill with water if the river overflows and thereforeprotecting the surroundingland.

1) Natural looking2) Does the damage the environment.   

1) Need a large area of land that is not being used. 2) Only come into use when the riverhas flooded.

Barriers, such as the Thames Barrier.

• The barrier is raised when a high tide or flood is forecast.

SOFT ENGINEERING

• These do not involve expensive structures, but instead uses the natural features of the drainage basin to control flooding.

• It involves planning the land use in the drainage basin.

• Forecasting and warning systems are also important

Floodplainzoning         

Local authorities and the national governmentintroduce policies to control urban developmentclose to or on the floodplain.     

1) A very cheap way of reducing the risk of damageto property.2) It is sustainable becauseit reduces the impact of flooding and buildingdamage is limited.3) Also because the flood-plain has not been built on,surface runoff is less likelyto cause flooding.

1) There can be resistance to restricting developmentsin areas where there is a shortage of housing.2) Enforcing planning regulations and controlsmay be harder in LICs.    

Washlands        

The river is allowed to floodnaturally into wastelandareas, to prevent floodingin other areas, for example,near settlements.    

1) Very cost effective as nothing is built.2) Provides potential wetland sites for birds andplants.3) The deposited silt may enrich the soil, turning the area into agriculturalland.

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

Warning systems      

A network of sirens whichgive people early warningof possible flooding. TheEnvironment Agency usesTV, radio, email, fax, text and phone messages tokeep people informed.  

1) A very cheap system.2) Electronic communicationis a very effective way ofinforming people.3) Because the people havewarning of floods they canmove valuable belongingsto safer places.

1) The sirens could bevandalized, so they aretested annually.2) There might not be enough time for residentsto prepare.   

Afforestation or Flood abatement Trees are planted in the 1) This is a relatively low 1) It is often conifers that

  catchment area of the river cost option. are planted which can

  to intercept the rainfall and 2) It improves the qulaity of make the soil acidic.

  slow down the flow of water the environment. 2) Dense tree plantations

  to the river. 3) Soil erosion is avoided as spoil the natural look of

    trees prevent rapid runoff the landscape.

    after heavy rainfall. 3) It increases fire risks

    4) Very sustainable. because of leaisure

      activities in the forest.

How can we manage the Cumbria Floods?

Use the map to help you suggest and explain which management techniques you would put in place. Hard or soft engineering? Where? Why?

Flood proofing

• This is where buildings are either designed or altered to make them less at risk of flooding.

• Do you recognise• this place?

1. Use the photo of Skipton, you have been given, to annotate with evidence of flood management. Try to identify evidence of the different types of hard and soft engineering.

2. Draw 2 spider diagrams, one for soft and one for hard engineering schemes and include their advantages and disadvantages.

The Environment Agency manage floods in England and Wales.

ACTIVITY:

Your task:• You work for the Cumbrian Flood Action Group.

• You have a brief to report to the Environment Agency and the Cumbrian County Council your views on the flood.

• Go back to the previous page where you have already:

• 1. Stuck the OS map of the area in to the centre of a double page,

• 2. Around the edge of the map included details on why it happened, it’s impacts (social, economic and environmental) and the responses to the event.( Put these in neat boxes with headings)

• NOW:

• 3. On the same map label your ideas on which hard and soft engineering techniques should be used to protect Cockermouth against a future flood event of this magnitude.

• Outline the benefits and problems of each around your base map.• You must also state your reasons for the choices you made (weighing up the balance between social,

economic and environmental benefits). Be prepared to present this to the rest of the class!

• Resources available to you:• You have been given a resources pack to help you produce your report, as well as a base map of the

area to detail your ideas for your flood alleviation plan.• Use your notes on methods of flood protection looked at in lessons.

Cumbrian Floods of 2009What are the proposals for flood alleviation?

Flood defence works begin!Innovative developments in Cockermouth.

What decisions have the Environment Agency made?

Open the sealed envelope to find out!

Plenary: Name and describe each method of flood management.

a.

b. c.

d.

e.f.

g.

Floodwalls Washlands

Relief channels

Flood warnings

Channelisation Floodplain zoning Afforestation

HARD SOFTEngineering Engineering

Floodwalls

WashlandsFlood relief channels

Flood warnings

Channelisation Floodplain zoning

Afforestation

FloodwallsFlood warningsFloodplain zoningWashlandsChannelisationFlood relief channelsAfforestation