Human Activities & River Landscapes (Edexcel GCSE Geography A)

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

• 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 

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