Managing River Flooding

Managing River Flooding

Gr. 9_2024/2025​

By Shanty Sinay

• how and why it takes place in drainage basin

• aspects that cannot be changed: rock type

• aspects that can be changed: amount of forest

• Hydrographs: to advise the authorities on flood management

• Hydrographs: shows how a river responds to a period of rainfall over a short period of time.

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To manage flooding​

• Opportunities vs hazard

• Risk: damage and loss of life

• Government priorities: to protect people and environment from flood

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​Some text here about the topic of discussion.

​Living on a flood plain

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Multiple Choice

What is the aspect of drainage basin that cannot be changed?

• river

• the rock type

• the amount of forest in an area

• hydrographs

Multiple Choice

What is used to advise the authorities on flood management?

• hydrologist

• hidrologic cycle

• hydraulic actions

• hydrographs

Multiple Choice

What is hydrograph?

• a graph that shows how a river responds to a period of rainfall over a short period of time

• a table that shows how a river responds to a period of rainfall over a short period fo time

• a graph that shows how a river responds to a period of flood over a short period fo time

• a graph that shows how a river responds to a period of rainfall over a long period fo time

​To stop the flood from happening

Flood prevention

​to have procedures to protect people and property in place

​​Flood protection

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​​Flood Management

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Open Ended

What is the difference between flood prevention and flood protection?

​​Hard engineering techniques​

​​Soft engineering techniques

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​​Ways to do flood prevention

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​​Dams

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​​Barriers and flood walls

​​embankment or levees

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Flood prevention: hard engineering​

​​Dredging and straigthening channels

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​​Canals and waterways

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​​Involves building artificial structures which try to control rivers, tend to be more expensive. Each hard engineering strategy has its advantages and disadvantages​

The dam traps water, which builds up behind it, forming a reservoir. Water can be released in a controlled way.

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​Advantages

• to produce electricity by passing the water through a turbine within the dam.

• Reservoirs can attract tourists.​

Dams and Reservoirs

The dam traps water, which builds up behind it, forming a reservoir. Water can be released in a controlled way.

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Dams and Reservoirs

​Disadvantages

• Very expensive.

• Dams trap sediment which means the reservoir can hold less water.

• Habitats are flooded often leading to rotting vegetation. This releases methane which is a greenhouse gas.

• Settlements are lost leading to the displacement of people. In developing countries locals are not always consulted and have little say in where they are relocated.​

​​Advantages

• More water can be held in the channel.

• It can be used to reduce flood risk in built-up areas.

Disadvantages

• Dredging needs to be done frequently.

• Speeding up the river increases flood risk downstream.

River straigthening and Dredging

​​Straightening the river speeds up the water so high volumes of water can pass through an area quickly. Dredging makes the river deeper so it can hold more water.

Open Ended

In river straightening, speeding up the river increases flood risk downstream. Expalin how this is possible.

​​Raising the banks of a river means that it can hold more water.

Embankment​

.Advantages

• Cheap with a one-off cost

• Allows for flood water to be contained within the river.

Disadvantages

• Looks unnatural.

• Water speeds up and can increase flood risk downstream.

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Advantages

• Removes excess water from the river channel to reduce flooding.

Disadvantages

• Expensive to build.

• If water levels continue to rise, the relief channel may also flood.

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Flood relief channel​

The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course.

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Flood prevention:
soft engineering​

​​It does not involve building artificial structures, but takes a more sustainable and natural approach to managing the potential for river flooding. Each approach has its advantages and disadvantages.

​​a system of sirens and warnings and evacuation procedures

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​​temporary, moveable metal barriers that can be put up quickly

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a store of sand and sandbags for emergency use​

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Flood prevention: soft engineering

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Advantages

• More expensive buildings and land uses are further away from the river, so have a reduced flood risk.

• Less damage is caused, leading to fewer insurance claims.

Disadvantages

• Not always possible to change existing land uses.

• Planners have to decide what type of flood to plan for.

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Floodplain zoning

Allowing only certain land uses on the floodplain reduces the risk of flooding to houses and important buildings.

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Multiple Choice

Two examples of hard engineering techniques are ....

• building dams and flood-plain zoning

• flood relief channel and providing sand bags

• river straigthening and building embankment

• river dredging and warning system

Open Ended

Mention one advantage and one disadvantage of building embankment.

Open Ended

Dams trap sediment which means the reservoir can hold less waterr. How can the reservoir hold less water because of this?

Case Study:

The Elbe River

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NO NEED TO DO THIS

​Study Source B on pg. 90

• Observe carefully all information that you can get from Source B: the colors, numbers, name of places, location, etc. (5 mins)

• Answer the following questions

Some text here about the topic of discussion

Open Ended

Suggest why much of the flooding took place in Germany after 2 June 2013.