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
Input
Water entering the system
Precipitation - any product of the condensation of
atmospheric water vapor that falls under gravity.
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
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
Channel flow: movement of water
through the river channel
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
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)