Drainage Basins

• Drainage basins :


  area surrounding river where rain falling on land flows into that river (river catchment)
• drainage basins are open natural systems that are local hydrological cycles
• watershed :


  boundary of drainage basin
• water balance :


  the balance between inputs & outputs
• water balance affects how much water is stored in drainage basins
• UK water basin seasonal patterns :

  wet seasons : precipitation exceeds evapotranspiration = water surplus = ground stores full = increased runoff & discharge = river level rises

  dry seasons : precipitate lower than evapotranspiration = ground stores depleted & some flows into river but isn't replaced

  end of dry season : water deficit in ground = refilled in next wet season
• Drainage basin inputs :

  1. Precipitation
• Drainage basin storage :

  1. Interception
  2. Ground water storage
  3. Soil storage
  4. Surface storage
  5. Channel storage
  6. Vegetation storage
• Drainage basin flows :

  1. Infiltration
  2. Overland flow / Runoff
  3. Throughfall
  4. Stemflow
  5. Throughflow
  6. Percolation
  7. Channel flow
  8. Baseflow
  9. Interflow
  10. Groundwater flow
• Drainage basin outputs :

  1. Evaporation
  2. Transpiration
  3. Evapotranspiration
  4. River discharge / River flow
• Zone of saturation :

  zone of soil/rock where all pores are full of water
• Water table :


  top surface of zone of saturation
• Aquifers :


  porous rocks that hold water
• precipitation :


  ways moisture leaves atmosphere to ground (main flow)
• interception :


  precipitation lands on vegetation/other structures before it reaches soil
• Vegetation storage :


  water taken up by plants / amount contained at 1 time
• Surface storage : 


  water in puddles , ponds & lakes
• Soil storage :


  moisture in soil
• Groundwater storage :


  water stored in ground (soil / rocks)
• Channel storage :


  water held in river / stream channel
• Infiltration :


  water soaking into soil
• Overland flow/runoff :


  water flowing over land
• Throughflow :


  water moving slowly downhill through soil
• Percolation :


  water seeping down through soil into water table
• Channel flow :


  water flowing in river/stream (river discharge)
• Transpiration :


  evaporation from within leaves