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2.1.2 - The Drainage Basin as a System
- Open system
- Water can enter and leave the system
- The drainage basin is a subset of the global hydrological cycle It is defined
as a catchment area forming part of the Earth's surface area which is
drained by a particular stream or river It is an open system which allows
energy and matter to be transferred across its boundary (the watershed
or drainage divide) from external areas
- Water can enter and leave the system
- Input
- Water entering the system
- Precipitation - any product of the condensation of
atmospheric water vapor that falls under gravity.
- Precipitation - any product of the condensation of
atmospheric water vapor that falls under gravity.
- Water entering the system
- Flow
- The movement of water between components
- Throughfall: Rainwater dripping from
leaves and branches towards the ground
(rain drops fall through the plants)
- Stemflow: Water flows along tree trunks and plant
stems towards the ground
- Infiltration: Downward movement of
water from ground surface into the soil
- Throughflow: Sideways movement of water through
the soil pores
- Percolation: Downward movement of water from soil to rock layer
- Groundwater flow: Movement of water through the rock layer
- Groundwater flow: Movement of water through the rock layer
- Throughflow: Sideways movement of water through
the soil pores
- Overland flow: Sheet of water moving along
the surface
- Two forms of overland flow
- Infiltration-excess: Intense rainfall
means not all water can infiltrate
soil, therefore runs along the surface
- Saturation-excess: Excessive
rainfall saturates soil so no more
water can infiltrate
- Infiltration-excess: Intense rainfall
means not all water can infiltrate
soil, therefore runs along the surface
- Two forms of overland flow
- Channel flow: movement of water
through the river channel
- Throughfall: Rainwater dripping from
leaves and branches towards the ground
(rain drops fall through the plants)
- The movement of water between components
- Store
- Where water is held in the system
- Interception: Water held on leaves and plant surfaces
- Vegetation store: Water within the biomass (plants and animals)
- Surface store: Water on the ground e.g. puddles
- Soil moisture store: Water held in soil
- Channel store: Water held in river channels
- Groundwater store: Water stored within rock layer
- Interception: Water held on leaves and plant surfaces
- Where water is held in the system
- Outputs
- Water leaving the system
- Channel discharge: Water leaving via river channels
- Evapotranspiration
- Evaporation
- Change of state from water to gas
(caused by temperature and wind
speed)
- Change of state from water to gas
(caused by temperature and wind
speed)
- Transpiration
- Water vapour released from plants
- Water vapour released from plants
- Evaporation
- Channel discharge: Water leaving via river channels
- Water leaving the system
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