Inputs
 The main input of a drainage basin is precipitation
 It is the deposition of moisture on earths surface from the atmosphere
 Varies in terms of type (snow/rain/dew/etc) quantity and intensity, duration
Outputs -there are usually two
 Evapotranspiratiom-EVT. This is a term combining both evaporation and transpiration
Evaporation is the loss of water is the loss of water from the surface to the atmosphere due
to heating. Transportation is the loss of water from plants via the stomata in leaves, after
uptake by the roots of water in the soil. EVT can account for 80% of water losses (outputs) in
equatorial drainage basin systems
 River discharge- this is the river flow, out of the channel and into the sea (or lake or another
drainage basin)
Evaporation- the physical process by which changes state from a liquid to gas and is lost from the
surface into the atmosphere due to heating. Rates of evaporation depend on the temperature of the
water and the air, the amount of humidity and wind speed
Transportation-when plants take up water through their roots from the soil and then lost through the
stomata in leaves. It is a biological process.
STORES:
• Interception - is the capture of raindrops by leaves and branches of vegetation which prevents precipitation
from reaching the ground directly. Some of this water may be lost from the system through evaporation.
• Soil moisture/soil water - this refers to subsurface water held in the pore spaces and around soil particles in
the soil.
• Surface water - any water sitting on the surface, whether in a puddle or dam is a form of surface water storage.
• Groundwater - refers to subsurface water in a zone of saturation in permeable rocks.
• Channel storage - once water reaches the river it could be considered channel storage for a brief time, before
flowing towards the sea or a lake.
FLOWS
Above ground:
• Throughfall (drip) - when intercepted water drips from the branches and leaves to the ground.
• Stemflow - when intercepted water trickles down tree trunks and plant stems to the ground.
• Overland flow/surface runoff - the surface discharge of water from rainfall or snowmelt down a slope, also
including surface discharge of underground streams (springs).
Below ground:
• Infiltration - the movement of water from the surface into the top layer of soil. Infiltration capacity is the
maximum rate at which rain can be absorbed into a soil in a given condition and it is expressed in mm/hr.
• Percolation - the downward moment of water through pores, joints and crevices within the mass of soil and/or
rock. It supplies the groundwater storage with water.
• Throughflow - the lateral downslope movement of water within the soil above the zone of saturation.
• Groundwater flow is a slow movement of water from groundwater storage to the nearest river channel
. •Baseflow is the part of a river’s discharge that is provided by the groundwater seeping into the bed of the river.
The two terms can be used interchangeably but there is a subtle difference.