River Flooding (Cambridge International IGCSE Geography)

Specification checklist

This content page covers the following sections of the specification:

• 1.3.2 - The human and natural causes of river flooding.
• 1.3.3- The impacts of river flooding.
• 1.3.4- An evaluation of the strategies and techniques used to manage river flooding, including sustainable

The causes of river flooding

Spec point — The human and natural causes of river flooding.

• When rivers cannot contain all the water they are transporting, a flood will occur
• Water flows out of the channel onto the floodplain
• Causes of flooding can be physical or human

Physical causes of river flooding

Precipitation type and intensity

• Intensive rainfall produces increased overland flow
• Heavy rain compacts the ground, reducing infiltration
• Rapid melting of snow can cause high rates of overland flow

Temperature and evapotranspiration

• Colder air can hold less water
• Lower temperatures lead to less evaporation, which means more water in the rivers

Drainage basin size and shape

• Smaller drainage basins respond more quickly to rainfall conditions, increasing the flood risk
• Circular basins respond more quickly to floods than linear basins, increasing the flood risk

Drainage density

• High drainage density is the result of impermeable rock/soil and increases overland flow

Slopes

• Steeper slopes reduce infiltration and increase overland flow

Vegetation types

• Deciduous trees lose their leaves in autumn, reducing the amount of interception in autumn and winter, which increases overland flow

Rocks and soil

• Impermeable rocks and soil decrease infiltration and percolation, which increases overland flow

Human causes of flooding

Urbanisation

• Urbanisation increases the magnitude and frequency of floods in three ways:

  • Creating impermeable surfaces, such as roads
  • Creating gutters and sewers, which increase drainage density
  • Riverside facilities reduce carrying capacity

• Urbanisation tends to have a greater impact on the lower section of the drainage basin due to there being more urbanisation in this section

Deforestation

• Similar impact to urbanisation
• Deforestation can increase overland flow
• Deforestation decreases channel capacity due to an increase in deposition in the channel
• In the Himalayas, there is evidence that changes in flooding and increased silt are due to high monsoon rains and unstable terrain

Agriculture

• Bare soil and ploughing increase the amount of overland flow

The impacts of river flooding

Spec point — 2.2.5 · The impacts of river flooding.

• There is a range of possible impacts of flooding
• These can be economic, social and environmental

Economic

• The cost of crop destruction will affect commercial farmers and increase food prices
• Destruction of infrastructure such as roads, energy supply and communications, which will then need to be repaired
• Increased insurance costs
• Reduction in house prices for those areas affected by the flooding
• Closure of businesses

Social

• Homes destroyed and damaged, leading to homelessness
• Increased food shortages and higher food prices caused by the loss of crops
• Deaths and injuries
• Difficulties in moving around the area due to damaged transport
• Loss of jobs
• Lack of clean water leads to disease
• Loss of energy supply

Environmental

• Destruction of animal habitats
• Loss of food supply for animals
• Pollution of the land due to pollutants carried by the water
• Death and injuries of animals
• Destruction of trees and other vegetation

Exam Hint There is often an overlap between the different categories of impact. It is important that you recognise the connections and, if appropriate, refer to them in your answers. For example, flooding leads businesses to close, which has an economic impact, but it also has a social impact because it means that people lose their jobs, and so their quality of life is affected.

Management of river flooding

Spec point — An evaluation of the strategies and techniques used to manage river flooding; including sustainable

Flood management

• The key cause of flooding is the amount and duration of precipitation; this cannot be altered

• There are several methods of managing floods and reducing the severity and/or impact

• The two main categories of flood management are hard and soft engineering:

  • Hard engineering involves building structures or changing the river channel
  • Soft engineering works with the natural processes of the river and the surrounding environment

• Soft engineering is increasingly popular

• Soft engineering is an example of mitigation where schemes aim to minimise damage rather than trying to prevent flooding

Types of hard engineering

• Dams and reservoirs enable the amount of discharge downstream to be controlled
• Embankments or levées increase the capacity of the river
• Straightened channels mean that the river flows more quickly past vulnerable areas, reducing the risk of flooding
• Flood relief channels allow some water to flow out of the main channel, reducing the discharge
• Spillways or overflow channels: these take excess water away from the main channel

Types of soft engineering

• River restoration supports the river by restoring it to its original regime—putting meanders back in, stabilising banks and connecting to flood plains

• Wetland conservation provides these areas as a place for excess water to go and slows the flow of floodwater

• Catchment management plans assess the risk of flooding in an area and outline how this will be managed

• **Floodplain zoning **means that only certain land uses are allowed on the floodplain, reducing the risk

• Afforestation is a long-term strategy (trees take time to grow), which**** involves the planting of vegetation and trees, it:

  • Increase interception and infiltration
  • Increases biodiversity
  • Reduces surface runoff

Additional flood control methods

• Other methods that can be used to decrease the risk of flooding are:

  • Leaving the stubble on the fields after the crop is harvested helps to stabilise the soil and increase infiltration
  • Contour ploughing involves ploughing fields across the slope rather than up and down. This gives the water more time to infiltrate and stops the ploughed furrows from becoming channels for water
  • Improved forecasting and flood warnings
  • Dredging the rivers to increase capacity, however, often leads to the need for concrete reinforcement of the banks

Sustainable Flood Management Strategies

• To be sustainable, a flood management strategy needs to both reduce flood risk and protect the environment

• Examples of sustainable strategies include:

  • Afforestation
  • River restoration
  • Wetland conservation
  • Flood storage areas

Exam Hint In the exam, you may be asked to "evaluate" the flood control methods. To ensure that you can do this, you need to know how effective the different methods are in reducing flooding. Examples of evaluation include:

• Soft engineering may be longer-term because strategies such as afforestation take time to work
• Hard engineering is effective in the short-term but is expensive and damages the environment.