River Flooding (Edexcel GCSE Geography: B (1GB0))

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Geography Lead

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

flood-events

Graph showing the increase in flood events over time

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

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

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)

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

to absolutely everything:

the (exam) results speak for themselves:

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