Flood Management - Hard and Soft Engineering Stratagies

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Dams - Hard Engineering

Dams

How it works

  • Huge wall built across river and a reservoir forms behind
  • Flood water caught behind dam, preventing downstream floods. The water is released steadily over the year

Benefits

  • Turbines can be built in dam,  to generate electricity
  • Steady release of water allows irrigation of land below all year
  • reservoir can be used for recreation (e.g fishing)

Disadvantages

  • Expensive
  • Reservoir creation = flooding => destryed farmland and people having to move
  • May affect wildlife ( ie. salmon swimming upstream to breed)
  • Sediment can get trapped => dam may fail AND can lead to erosion downstream
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Channel straightening - Hard engineering

Channel straightening

How it works

  • River is straightened (meanders removed)
  • Artifical cut-throughs allow the water to flow faster
  • Flooding reduced as water drains downstream faster.

Benefits

  • Navigation is easier as river is straighter and shorter

Disadvantages

  • Flooding can occur downstream
  • More erosion downstream
  • altering the channel disturbs wildlife habitats
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Levees - Hard engineering

Levees

How it works

  • Embankments built along river
  • Increase bankfull level so it is less likey to flood (discharge < bankfull level)

Benefits

  • Allow flood plain to be built on

Disadvantages

  • Quite expensive
  • Risk of severe flooding if they are breached
  • Can prevent flood water draining back into river if flooding does occur
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Diversion spillways - Hard engineering

Diversion spillways

How it works

  • Channels that take water elsewhere if water level is too high (water diverted around important area or to another river)
  • Prevent flooing as discharge it reduced
  • Often have gates so the reelease of water can be controlled.

Disadvantages

  • There is and increase of discharge when spillway rejoins main channel which can lead to flooding at this point in the river
  • If spillways are overwhelmed areas not used to flooding can be flooded which can cause bigger problems
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Land use management -Soft engineering

Land use management

How it works

  • Planning retrictions prevent roads of buildingd being built on the flood plain and use of flood plain resricted to playing fields, allotments or parks
  • More water can infiltratie = surface runoff drecreased = discharge reduced

Benefits

  • No roads of buildings damaged by flooding = less damage if flooding occurs
  • provides recreational oppurtunities

Disadvantages

  • Restricts development (problematic in areas with housing shortages)
  • Can't be used in areas already urbanised
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Wetland and river bank conservation - Soft enginee

Wetland and river bank conservation

How it works

  • Wetlands store water and slow it down = reducing flooding downstream
  • Conserving them = natural protection
  • Planting trees and shrubs on banks increases interception and lag time and reduces discharge

Benefits

  • Vegetation protects surface soil from erosion and provides habitats for wildlife

Disadvantages

  • Less land available for farming
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River restoration -Soft engineering

River restoration

How it works

  • Making the river more natural (i.e. removing man-made levees) allowing river to flood natrually
  • As flood plains flood, discharge in channel is reduced reducing flooding downstream.

Benefits

  • Little maintenance needed
  • Creates habitats

Disadvantages

  • Local flood risks can increase
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Alteration or urban surfaces - Soft engineering

Alteration or urban surfaces 

How it works

  • Building porous pavements or soakways increases infiltration and reduces runoff, which increases lag time and reduces discharge

Benefits

  • Any pollutants in the water are filtered out by the soil before water eaches the channel

Disadvantages

  • Expensive
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Weather forecasts and flood warnings - REDUCING IM

Weather forecasts and flood warnings

How it works

  • The Environment Agency monitiors weather forcasts, rainfall and river discharge
  • They issue warnings using media (i.e. TV, radio, newspapers and the internet)
  • Gives people time to prepare (i.e. evacuate, move possessions, use sand bags)

Disadvantages

  • Some people may not be able to access communication network
  • Flashfloods may happen to fast for warnings
  • People may ignore the warnings if they have been in accurate in the past
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