Human Activities on River Landscapes (Edexcel GCSE Geography A): Revision Note
Exam code: 1GA0
Causes & Effects of 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
Graph showing the increase in flood events over time
The increased flood risk is the result of both physical and human factors
Physical Factors Which Increase Flooding Risk
Physical Factor | Reasons for Increase in Surface Run-off |
Relief | Steep slopes reduce infiltration |
Geology | Impermeable rocks reduce percolation |
Soil | Frozen, saturated or compacted soil reduces infiltration Some soil types, such as clay, reduce infiltration |
Rainfall | Heavy or prolonged rainfall means that the rate at which water reaches the surface exceeds the infiltration rate After a period of snow, rising temperatures can cause rapid melting |
Seasonal Variations | Flooding in Northern Europe tends to occur in the autumn and winter, when rainfall is more frequent In areas affected by monsoon, much of the annual rainfall occurs in a few weeks, saturating the ground Higher temperatures in spring lead to snow melt in mountainous areas |
Drainage basin | Where drainage density is high, there are many tributaries taking water to the main channel, causing a rapid increase in discharge |
Vegetation | Where there is little natural vegetation, there is reduced interception |
These all increase surface run-off (overland flow) and decrease the lag time
This means that water reaches the river more quickly
The result is that the river's capacity is more likely to be exceeded, leading to a higher flood risk
Flood (storm) hydrographs
Prediction of flooding means that steps can be taken to manage flooding
Flood hydrographs are used to predict the reaction of a river discharge to a rainfall event
A flood hydrograph shows the changes in river discharge after a storm event
The graph shows a short period of time, usually 24 hours
The flood hydrograph has a number of features:
Base flow
Peak rainfall
Rising limb
Peak discharge
Lag time
Recessional limb
Flood Hydrograph in an Urban Area
Impacts of increased flood risk
There are a range of possible impacts of flooding
These can be both human and physical
Possible Impacts of Flooding
Human | Physical |
Homes destroyed and damaged, leading to homelessness | Destruction of animal habitats |
Damage to crops and agricultural land 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 floodwater |
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 |
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Loss of electricity and gas when water gets into the supply |
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Impact of Human Activity on River Processes
As well as physical factors, human activities impact on rivers, their processes and landscape
Urbanisation
Urbanisation has led to an increase in the land covered by impermeable surfaces, including tarmac and concrete
Water flows into the drains and reaches the rivers more rapidly
Increasing areas of river floodplains are being built on
This reduces the areas where water can go when a flood occurs
The construction of urban areas may lead to river channel alterations, such as channel straightening
This impacts on the natural processes of the river
It can increase erosion and deposition downstream
Agriculture
Areas of trees and vegetation are cleared to make way for crops and grazing
This reduces interception and infiltration
Surface runoff increases and water reaches the rivers more quickly
Irrigation leads to increased water abstraction
This reduces the discharge in the river
It may lead to increased deposition and a decrease in erosion
Fertilisers and pesticides used in farming are washed from the soil into the water system affecting the river ecosystem
Ploughing creates channels which increase the amount of surface run-off
The surface run-off transports sediment into the rivers
The sediment builds up on the river bed, decreasing the river capacity
Industry
Abstraction of water for industry reduces the discharge in the river
This may lead to increased deposition and a decrease in erosion
Solid and liquid industrial waste pollutes rivers, which impacts the river ecosystem
Examiner Tips and Tricks
In the exam, you may be asked to explain the causes of flooding. Remember this means that you need to give connections between factors such as deforestation and the increased flood risk. Rather than simply stating that deforestation increases flood risk you need to explain the reasons - decreased interception and infiltration, leading to increased overland flow and shorter lag time.
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