5.5B Human actions that can exacerbate flooding

• • Human activity can exacerbate flood risk as a result of: -> Changing land use in the drainage basin -> Mismanagement of the river using hard engineering
• Changing land-use causes flooding:

  • Deforestation reduces the amount of interception and infiltration 
  • Overgrazing removes the vegetation and so increases bare soil, which animals compact under hoof, reducing infiltration rates and increasing runoff
  • Ploughing compacts the soil reducing soil porosity and less storage capacity
  • Farming often reduces vegetation cover and increase soil compaction from tractors and machinery, this reduces the amount of water infiltration and increases surface runoff
  • Urbanisation increases impermeable surfaces
• Mismanagement of a river channel causes drought:

  • Channelisation adds a liner to a straightened river channel to reduce friction which aims to improve flow rate
  • Dams, floodwalls and reservoirs are built to prevent flooding and ensure a regular supply of water
  • Embankments and levees can be built or increased in height to improve bankfull capacity, using concrete or sustainable materials
  • River straightening increases the flow of water by increasing the gradient of a river's channel and removing natural meanders