Unit 1 topic 1

• Hydrological cycle


  The continuous movement of the earth's water
• Water


  • Can change state (liquid, vapour, ice)
  • Changes state at various speeds
• The amount of water on earth is always the same
• The hydrological cycle is a closed system
• Drainage basin


  An area of land drained by a river and its tributaries
• Drainage basin


  • Edge is marked by a boundary watershed
  • Range in size from local to large systems (e.g. Nile)
• Movement of water in drainage basin

  1. Shown through Drainage Basin Hydrological cycle

  2. Cycle has inputs (precipitation) and outputs (evapotranspiration and runoff)
• Water balance


  The difference between the inputs and the outputs (the subsequent change in storage) in the drainage basin
• If precipitation exceeds runoff and evapotranspiration, there will be a positive water balance and the amount of water stored will increase
• If runoff and evapotranspiration exceeds precipitation, there will be a negative water balance and the amount of water stored will decrease
• Water balance equation


  • P=Q+E+ Change in storage
  • P=Precipitation
  • Q=Runoff
  • E=Evapotranspiration
• Groundwater


  Any water underground that can be held in soils or between the spaces in rocks
• Groundwater makes up around 30% of all the earth's freshwater
• Aquifers


  Underground water stores
• Shallow groundwater aquifers can store water for up to 200 years, deeper fossil aquifers can last for up to 10,000 years
• Water table


  The boundary between the unsaturated and saturated zone underground
• Groundwater recharge


  When groundwater levels are reduced, groundwater can be recharged by precipitation infiltrating the ground
• Groundwater is recharged mainly in winter when there are high precipitation levels and low evaporation rates
• Groundwater can also be recharged through surface water storage - lakes and rivers seeping into groundwater stores
• Difference between water table and groundwater

  Water table refers to the level below ground that is saturated with water, groundwater is the water that comes from this saturated ground
• Soil moisture budget


  The change in the amount of water stored in the soil throughout the year, mainly affected by precipitation and potential evaporation
• Potential evaporation


  The amount of evapotranspiration that could occur if sufficient water was available in the system, linked to temperature
• Often the atmosphere's ability to hold water vapour (potential evaporation) is greater than the amount of water available
• Hydrograph


  A record of a river's discharge over time
• Types of hydrographs


  • Annual hydrographs (river regimes)
  • Storm hydrographs (flood hydrographs)
• Parts of a storm hydrograph

  • Peak rainfall
  • Peak discharge
  • Lag time
  • Rising limb
  • Falling limb
  • Base flow
• Factors affecting overland flow and hydrograph shape

  • Size of basin
  • Shape of basin
  • Drainage density
  • Relief of the land
  • Rock and soil type
• Physical factors affecting hydrological hydrograph

  • Storms and precipitation
  • Seasonal changes and vegetation
  • Temperature
• Human factors affecting hydrological drainage basin system and hydrograph shape

  • Land use change (urbanisation, deforestation)
  • Farming practices
  • Water abstraction
• In Europe, the dominant source of freshwater is groundwater, which is often pumped from the ground quicker than it is replenished, leading to sinking water tables and saltwater intrusion in coastal areas