Water extraction

• Water extraction


  Extracting water from surface and groundwater to meet public, industrial and agricultural demands
• River Kennet


  • Drains an area of 1,200 km²
  • Upper catchment mainly chalk (highly permeable) - groundwater contributes most to Kennet's flow
  • Diverse range of habitats and wildlife
  • Exceptionally high oxygen levels
• Water extraction from River Kennet

  Reduced flows by 10-14%
• 2003 drought


  Flows fell by 20%
• Reduced groundwater levels


  Caused springs and seepages to dry up, reduced incidence of saturated overland flow on chalk uplands
• Aquifer


  Permeable or porous water-bearing rocks such as chalk, New Red Sandstone
• Artesian basin


  Sedimentary rocks form a synclinal or basin-like structure, aquifer confined between impermeable rock layers, groundwater under artesian pressure
• London Basin


  • Located in the centre of a synclinal structure, groundwater in chalk aquifer trapped between impermeable London Clay and Gault Clay
  • Rainwater enters chalk aquifer where it outcrops on the edges of the basin in the North Downs and Chilterns
  • Groundwater flows by gravity towards the centre of the basin
  • Wells and boreholes in London under artesian pressure
• Overexploitation of groundwater in London


  Caused a drastic fall in water table of nearly 90m since 1900
• Declining industrial water demand in London

  Allowed water table to recover
• Rising water table in London in the early 1990s at a rate of 3mm per year began to threaten underground tunnels</b>
• Abstraction licenses were granted to slow the rise in water table, which is now stable
• Seasonal changes in water table

  • Summer - storage of water decreases, some wells dry up
  • Winter - water table higher, all wells in artesian basins are artesian