CAUSES OF FLOODING

• precipitation (physical)


  • depends on how quickly precipitation gets into the river channel
  • surface runoff is the fastest
  • continuous heavy rain results in a higher discharge
  • sudden bursts of heavy rainfall results in infiltration being slow
  • prolonged light rainfall if the soil is already saturated
• relief (physical)


  • height and slope of land
  • steep slopes - more surface runoff
  • steep sided valleys
  • low lying flood plains - no slope for surface runoff
• geology (physical)


  • rock found in mountains is impermeable rock
  • the rock is bare with thin soils and little vegetation to intercept rain
  • low lying areas contain impermeable clay - difficult for infiltration
  • flooding is less likely in areas of permeable rock
• urbanisation (human)


  • greater area covered by buildings and roads
  • homes are being built on greenfield sites
  • houses being built on flood plains
• deforestation (human)


  • reduces interception and rocks no longer take water form soil
  • soil becomes saturated, surface runoff occurs and river discharge increases
• farming (human)


  • bigger fields = less hedges = less interception
  • once crops are harvested there is not interception from the vegetation
  • fields soak up rainfall through infiltration, using polytunnels to extend growing season reduces this ability of infiltration