fw.1.1 The drainage basin as an open system

News article

Colorado River basin has lost nearly the equivalent of an underground Lake Mead

Reservoir lost 27.8m acre-feet of groundwater in 20 years, study finds, vanishing ‘twice as fast as surface water’

The Guardian · 27 May 2025

Key terms

• Aquifer
  • A body of rock and/or sediment that holds groundwater.

• Atmospheric storage
  • The storage of water in the atmosphere in the form of water vapour, clouds, and precipitation.

• Channel flow
  • The movement of water within the river or stream channel.

• Channel storage
  • The water held in a river or stream channel, including pools and slower-moving sections.

• Closed system
  • A system that does not exchange matter with its surroundings, but can exchange energy.

• Confluence
  • The point where two or more rivers or streams meet and merge into a single watercourse.

• Discharge
  • The volume of flow of water in a channel, measured in cubic metres per second (cumecs).

• Drainage basin
  • The area of land drained by a river.

• Evaporation
  • The process by which water is transformed from liquid to vapour, transferring from surfaces like lakes, rivers, or moist soil into the atmosphere.

• Evapotranspiration
  • The sum of evaporation from the land surface plus transpiration from plants.

• Groundwater
  • The water that resides under the surface of the earth, typically in porous rock formations known as aquifers.

• Groundwater discharge
  • The natural or artificial removal of groundwater, such as springs or wells, to the earth's surface or into bodies of surface water.

• Groundwater flow
  • The movement of groundwater through the soil and rock layers beneath the earth's surface.

• Groundwater storage
  • Water stored underground in the zone of saturation.

• Ice storage
  • Water stored in the form of ice, such as in glaciers, ice caps, and ice sheets.

• Impermeable
  • Not permeable.

• Infiltration
  • The process by which water on the ground surface enters the soil, moving into the subsurface layers.

• Infiltration capacity
  • The maximum rate at which soil can absorb water, often influenced by soil type, moisture content, and land cover.

• Inputs
  • Are the elements that go into a system.

• Interception
  • The process by which precipitation is caught and held by vegetation, buildings, or other structures, preventing it from reaching the ground immediately.

• Interception storage
  • The temporary retention of precipitation by leaves, branches, and other surfaces before it either evaporates, falls to the ground, or flows as stemflow.

• Open system
  • A system that exchanges matter and energy with its surroundings.

• Outputs
  • Whatever comes out of the system.

• Percolation
  • The movement of water through the soil itself.

• Permeable
  • A property of soils and rocks indicating their capacity for transmitting water.