Flooding

Flooding

1. MEDC flood

   • Cumbria (December 2015)
     • Confluence of the Cocker and the Derwent
       • X2 the volume of water
     • 348m of precipitation in 24 hours
       • water fallen on already saturated ground
         • antecedent moisture
     • Imapcts
       • £250 million lost in the cost of damage
       • Dozens of domestic UK flight were cancelled
       • In Cumbria and Lancashire more than 43,000 homes suffered from a power cut
       • floor of a toy shop in Cockermouth was ruined by flood water
         • happened near Christmas (busiest time of the year) income decreased

2. LEDC Flood

   • Pakistan 2010
     • River Indus
     • Monsoon, 60 hours of continuous heavy rainfall
     • Impacts
       • 1.2 million homes damaged
       • £1.5 million lost in agriculture
       • 1600 people died
         • these people could have been the breadwinner so this means that there is less money in the family and this may result in poverty
       • 20% of tree plantations created in the 2009 – 2010 afforestation project were ruined
         • there was less interception and increased the intensity of future floods
           • the soil is also more susceptible to soil erosion so the vegetation is unlikely to re-establish itself
     • 20% of Pakistan was flooded
     • levees were formed
       • in Pakistan sediment was eroded off the Himalayas and this caused levees on the walls of the channel
     • deforestation
       • Taliban were cutting down trees

3. Hard Engineering strategy

   • Dams
     • Three Gorges Dam in China
       • Yangste River
       • Generates hydroelectric power
         • 20,000 megawatts an hour
         • Enough electricity for 60 million homes in China
       • 150,000 acres of land had to be cleared
         • Destroy habitats
         • 1 million people had to move away from the river
       • Employment
         • 40,000 jobs created when the dam was being built and maintained
       • Cost of the dam- 15 billion dollars
         • Took 17 years to build
     • Reduces flooding as water is held in a reservoir behind the dam which can be controlled
       • China
         • In 1931, 135,000 people died due to flooding
       • However it stops nutrients reaching the land downstream
         • Crops fail
           • Farmers income decreases

4. Soft engineering strategy

   • Afforestation
     • More interception so there is less infiltration so this means that there is less surface runoff so it takes more time for the water to get to the river channel
   • River restoration
     • Allowing the river to meander means that the velocity decreases
       • flooding happens in these areas rather than downstream where the town and houses are located
     • At HIghland water (tributary of the River Lymington) Warwick Slade Lawn is the section of highland water that was modified
       • Start date- June 2009
         • End date- November 2009
       • 150m of the river
       • £200.000 total costs
   • Floodplain zoning
     • Using previous floods to predict future floods
       • You know not to build on a floodplain because this is an area where there flooding

5. Causes of flooding

   • Human causes
     • Deforestation
       • Removing trees
         • Less interception and less water is held in plant storage
           • Water gets to the channel faster
             • Surface runoff increased
               • Lag time reduced
         • for example this happened in Pakistan and therefore increased the impacts and the cause of the flood
     • Urbanisation
       • more concrete surfaces
         • water can not infiltrate
           • more surface runoff
   • Natural causes
     • Climate change
       • more precipitation
         • more water in the drainage basin system
       • increased temperatures
         • more evapouration so there is less water
         • ground goes harder due to evapouration
           • less infiltration
     • steeped sided slopes
       • higher gravitational potential energy
         • increased velocity
     • Rock type
       • impermeable rocks means that theres less infiltration