Local Scale

• In a local drainage basin system, water may be lost as an output through evapotranspiration and runoff, but more water may be gained as an input through precipitation. As the inputs and outputs are not balanced, it is an open system.
• 𝙄𝙉𝙋𝙐𝙏𝙎:

  • Precipitation: Any water that falls to the surface of the earth from the atmosphere including rain, snow and hail.
• 𝙊𝙐𝙏𝙋𝙐𝙏𝙎:

  • Evapotranspiration: Compromised of evaporation and transpiration. Evaporation occurs when water is heated by the sun, causing it to become a gas and rise into the atmosphere.
  • Transpiration occurs in plants when they respire through their leaves, releasing water they absorb through their roots, which then evaporates due to heating by the sun.
  • Streamflow: All water that enters a drainage basin will either leave through the atmosphere or through streams which drain the basin. These may flow as tributaries into other rivers or directly into lakes and oceans.
• 𝗣𝗘𝗥𝗖𝗢𝗟𝗔𝗧𝗜𝗢𝗡:

  • Water moves from the ground or soil into porous rock or rock fractures.
  • The percolation rate is dependent on the fractures that may be present in the rock and the permeability of the rock.
  • Slow flow
• 𝗧𝗛𝗥𝗢𝗨𝗚𝗛𝗙𝗟𝗢𝗪:

  • Water moves through the soil and into streams or rivers.
  • The speed of flow is dependent on the type of soil.
  • Clay soils with a high field capacity and smaller pore spaces have a slower flow rate.
  • Sandy soils drain quickly because they have a lower field capacity, larger pore spaces and natural channels from animals such as worms.
  • Moderate/fast flow
• 𝗦𝗨𝗥𝗙𝗔𝗖𝗘 𝗥𝗨𝗡𝗢𝗙𝗙 (𝗢𝗩𝗘𝗥𝗟𝗔𝗡𝗗 𝗙𝗟𝗢𝗪):

  • Water flows above the ground, as sheetflow (lots of water flowing over a large area), or in rills (small channels similar to streams, that are unlikely to carry water during periods where there is not any rainfall)
  • Fast flow