8. Fluvial Processes and Landforms Flashcards
what is the most widespread and geomorphic agent on land.
rivers
They occur in diverse environments, even in deserts
The river channel is formed when
surface run-off is concentrated into a long depression
Tiny rills and larger masses of sheet flow coalesce to form
The channel
The width and depth of the channel vary along its
course
As the water flows downhill under gravity seeking sea level or its base level, the channel reflects what?
the fluvial processes
a drainage basin is
an area of land drained by a river and its tributaries
A drainage basin boundary is marked by?
a ridge of high land beyond which any precipitation will drain into adjacent basins.
This boundary is called a watershed
watershed (drainage basin) is the
The land from that delivers surface water, sediment and dissolved substances into a particular river, lake, wetland, or other body of water.
A drainage basin may be described as what type of system?
a open system
If a drainage basin is viewed as a system then its characteristics are
inputs in the form of precipitation (rain and snow)
outputs where the water is lost from the system either by the river carrying it to the sea or through evapotranspiration
Within this system,
some of the water is stored;
in lakes and/ or in the soil, or
passes through a series of transfers or flows,
e.g. infiltration, percolation, throughflow
evapotranspiration is
the loss of water directly from the ground, water surfaces and vegetation
figure3.1 The drainage basin as an-open system
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the greater the intensity of a storm
the shorter its duration
Convectional thunderstorms are short, heavy and may be confined to small areas,
whereas the passing of a warm front of a depression will give a longer period of more steady rainfall extending over the entire basin
Evaporation is
the physical process by which moisture is lost directly into the atmosphere from water surfaces, including vegetation and the soil, due to the effects of air movement and the sun’s heat
Transpiration is a
biological process by which water is lost from a plant through stomata in its leaves
Evaporation rates are affected by what?
temperature
wind speed
humidity
hours of sunshine and other climatic factors
Transpiration rates depend on
the time of year
the type and amount of vegetation
the availability of moisture and
the length of the growing season
example of how it is possible to distinguish between the potential and the actual evaporation spiration of an area
in deserts there is a high potential evapotranspiration because the amount of moisture that could be lost is greater than the amount of water actually available
On the other hand, in Britain the amount of water available for evapotranspiration nearly always exceeds the amount which actually takes place
hence the term actual evapotranspiration
transpiration is limited by
the availability of water in the soil
Interception storage is
The first set of precipitation that falls on the vegetation surfaces (canopy) or human-made cover and is temporarily stored on these surfaces which shelters the underlying ground
Intercepted water either can be evaporated directly to the atmosphere, absorbed by the canopy surfaces or ultimately transmitted to the ground surface.
interception storage is greater where?
is greater in a woodland area or where tree crops are grown
than on grass or arable land
