River Flooding (Edexcel GCSE Geography B)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Risks from River Flooding
River floods are one of the most common natural hazards
The risk from river flooding around the world has increased over the past 50 years
The increased flood risk is the result of human factors outlined in the sections on hydrography and human activity - they include
Deforestation
Agriculture
Urbanisation
These all increase overland flow/run off and decrease the lag time
The result is that the river's capacity is more likely to be exceeded leading to a higher flood risk
Climate change may lead to increased rainfall or frequency of storms which increases the discharge
River channel management upstream can increase discharge downstream for example straightening the channel will increase the speed the water moves downstream increasing the risk of the river capacity being exceeded
Impacts of increased flood risk
There are a range of possible impacts of flooding
These can be both social and environmental
Possible Impacts of Flooding
Social | Environmental |
|---|---|
Homes destroyed and damaged leading to homelessness | Destruction of animal habitats |
Damage to crops and agricultural land which increases the chances of food shortages and food price increase | Loss of food supply for animals |
Death and injury | Pollution of land due to pollutants such as sewage and diesel in the flood water |
Damage and destruction of transport routes (road and rail) | Death and injury of animals |
Loss of jobs due to the damage and destruction of businesses | Destruction of trees and other vegetation |
Loss of clean water supply as contaminated water enters the supply |
|
Loss of electricity and gas when water gets into the supply |
|
Worked Example
Explain one way in which human activity can increase the risk of river flooding
(2 marks)
Answer
Building on floodplains/urbanisation (1) which can reduce infiltration and/or puts more people/property at risk (1)
Deforestation (1) which reduces infiltration and so increases runoff making rivers ‘peakier’ (1)
River channel management preventing river flooding upstream (1) so making river discharge larger downstream thus increasing risk (1)
Climate change idea (1) increasing rainfall and/or making weather stormier increasing discharge (1)
Managing Flood Risk
The key cause of flooding is the amount and duration of precipitation this cannot be altered
There are a number of 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 natural processes of the river and 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 the flooding
Cost and Benefits of Hard Engineering
Method | Benefits | Costs |
|---|---|---|
Dams and reservoirs | Enables the amount of discharge downstream to be controlled | Expensive to build Can affect habitats downstream |
Embankments and levees | Increase the capacity of the river Use natural materials which blend with the environment | May fail due to erosion or water overtopping Can be expensive Increase flood risk downstream |
Dredging | Increases river capacity as it removes sediment from the river bed | Needs to be carried out regularly Increases flood risk downstream |
Flood relief channels | Allow some water to flow out of the main channel reducing the discharge and protecting areas in the immediate area | Can lead to flooding elsewhere |
Flood walls | Low maintenance Relatively low cost | Increases flood risk downstream Block the view of the river |
Costs and Benefits of Soft Engineering
Method | Benefits | Costs |
|---|---|---|
River restoration | This supports the river by restoring it back to its original regime: putting meanders back in, stabilising banks and connecting to flood plains | It involves land use change that the local population may not want |
Washlands | Areas are left undeveloped so that the floodwaters can flow on to them. This reduces discharge within the river channel | Reduces the land available for development and agriculture |
Floodplain retention | Means that only certain land uses are allowed on the flood plain, reducing flood risk Provides areas for leisure and recreation | Reduces the land for development and agriculture |
Afforestation | Reduces discharge by increasing infiltration and interception | Not possible in all areas |
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 which involves ploughing fields across the slope rather than up and down. This gives the water more time to infiltrate and stops the ploughed furrows becoming channels for water
Improved forecasting and flood warnings
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