5.2A Hydrological cycle processes

• • Drainage basins are subsystems of the global hydrological cycle, they drain all the water which lands on the Earth's surface
  • An individual drainage basin is the area drained by a river and its tributaries, this is also known as the catchment area
  • The boundary of the drainage basin is the watershed
• Drainage basin example:

  • the Nile River basin drainage area is more than 3 million km2 over 12 countries with 73 % of the drainage basin in Sudan and Egypt

  
• Drainage basin key features:

  • Watershed
  • Source
  • Confluence
  • Tributary
  • Mouth

  
• Orographic rainfall = where warm, moist air is forced to rise over high ground, which then cools and condenses forming clouds which release precipitation

  
• Frontal rainfall = when warm and cold air masses meet and the warm air rises over the cold air, causing condensation of clouds, causing precipitation

  
• Convectional rainfall = occurs when the ground heats the air above it, warm air rises which the cools causing clouds and then precipitation

  
• Interception = when plants/leaves/vegetation intercepts the falling precipitation

  -> Can prevent as much as 40% of precipitation reaching the ground
• Infiltration = where water enters small openings and pores in the ground from the surface.
• Throughflow = the lateral (sideways) movement of water through the upper soil, along lines of seepage called percaline
• Percolation = where water flows down through the soil layers and underlying rock is pulled down through gravity

  -> rate of travel is determined through porosity (soil) and permeability (rock)
• Groundwater flow = water that has infiltrated and percolated into the bedrock and below the water table to feed springs, river channels and recharge aquifers 
• Watershed


  The area of land that drains into a particular river, lake, or other body of water. Also known as a drainage basin or catchment area.
• Source


  The starting point of a river or stream, where the water originates. This could be a spring, a lake, or even melting snow.
• Confluence


  The point where two or more bodies of water meet and combine. This could be two rivers, a river and a stream, or any other combination of flowing water.
• Tributary


  A smaller stream or river that flows into a larger one. Tributaries contribute to the flow of the larger river and help to increase its volume.
• Mouth


  The ending point of a river, where it empties into a larger body of water such as a sea, lake, or ocean.