the drainage basin system

what is a drainage basin

a drainage basin is an area within which water supplied by percipitation is transferred to the ocean a lake or larger stream it includes all of the area that is drained by a river and its tributaries

throughflow

the downslope movement of water within the soil towards the river channel parallel to the surface

stem flow

water which has been intercepted by vegetation and reaches the surface by flowing down the tree trunks or stems

percolation

the downward movement of water after infiltration through the pores in the subsoil into the bedrock and joints and cracks in rock

throughflow

where precipitation is not intercepted by the vegetation and is able to fall directly onto the ground.

surface runoff

the movement of water across the surface of the earth due to over saturation of soils or impermeable surfaces, or when rates of rainfall exceed speed of infiltration

infiltration

the vertical movement of water entering the soil from the surface

interception

the trapping of water during a percipitation/rainfall even on leaves of vegetation

evaporation

the loss of water from the earths surface via the change of water to gas through the application of heat

groundwater flow

the slowest down spline movement of water through the deep bed rock

base flow

the groundwater flow that slowly enters the river from seeping in the ground(not a result of the throughflow or surface runoff

evapotranspiration

the loss of water from land water and vegetation via the combined process of evaporation and transpiration from the stomata/leaves of vegetation

river discharge

the volume of water passing a fixed point at a given time

cross sectional area x velocity=discharge

measured in cumecs

percipitation

process by which water is transferred from the atmosphere to the earths surface in the form of rain hail sleet or snow

input to the drainage basin system

drainage basin system

factors effecting evaporation

temp

humidity

winds speed(displaces the moustire layer on a puddle allowing evaporation rates to increase)

vegetation cover

vegetation colour-light=low as light reflected

dark=quick as light absorbed

field capacity

refers to the amount of water held in the soul after excess water drains away that is saturation or near saturation

infiltration capacity

is the maximum rate at which rain can be absorbed by soil in a given condition

antecedent soil moustire

is the pre existing levels of soil moisture

soil moisture deficit

the degree to which soil moisture falls below field capacity.

soil moisture recharge

occurs when precipitation exceeds potential evapotranspiration there is some refilling of water in the dried up pores of the should

soil moustire surplus

is the period when soil is saturated and water cannot enter and so flows over the surface

soil moustire utilisation

is the process by which water is drawn to the surface through capillary action

porosity

is the capacity of a rock to hold water

permeability

the ability to transmit water through a rock via joints and fissures

springs(underground water)

the point at which water emerges from the ground either where throughflow is impeded and has to rise to the surface or where underground water is held in an aquifer and water level is raised to the surface through recharge.also result of impermeable zones

water table(underground water)

upper surface of the saturated zone where soil/rock pres are filled with water

rises in wet reasons(rain or snowmelt) falls in dry periods

recharge(underground water)

water movement from the surface(infiltration) deep percolation of water into saturated zone

ground water

the subsurface water that is stored under the surface in the rocks it accounts for 96% of all freshwater on earth