4. A drainage basin
An area of land drained by a river and its tributaries where
any precipitation is collected or drained into it.
Its boundary is marked by a ridge of high land called
watershed
Drainage basins have one main stream and many
tributaries
5. Watershed: A stretch of land that surrounds drainage basin (a.k.a. boundary)
Drainage Basin: A river system that collects rainwater and comprises of streams and river
Tributaries: Streams that flow in the river which is mainly found in the upper course.
Distributaries: Branch out from the river which is mainly found in the river delta.
River Source: Point where the river starts
River Mouth: Place where the river meets the sea / ocean (River ends)
6. A drainage basin may be described as an open
system.
It forms part of the hydrological cycle
7. Characteristics of a drainage basin
are:
Inputs : - in the form of precipitation
Outputs:- water is lost through
evapotranspiration
Within the system, some of the water:
Is stored in water storage such as lakes or soil
Passes through a series of transfers or flow e.g. infiltration,
percolation and throughflow
8.
9. Important terms..
Interception : precipitation lands on vegetation.
Infiltration : Water that reaches ground surface will soak into soil.
Overland flow : water moving over the ground.
Throughfall : precipitation passing through the plant canopy
Percolation : Some water sinks deep into the earth (percolates)
through openings in the soil.
Stemflow : water that flow down tree trunks or plant stems.
Groundwater : water transfer through permeable rocks from the soil
above.
Baseflow : water flows from groundwater stores to the stream
Throughflow : water moving through the soil. Surface run-off : water
that flows over the land surface.
10. main input - precipitation.
The type: rain or snow,
hail, etc.
Factors affecting the
amount of water in the
system:
the intensity,
the duration and
frequency.
Each subsystem of the
drainage basin system will
also have
inputs and ouputs, and
the output from one stage
of the diagram will form the
input for another.
11. Water stored - on the surface,
- in lakes and channels
or
- in the groundwater
store.
Reach groundwater via infiltration and
percolation.
some water will be stored in the soil
and rock.
The amount of water stored will vary
depending on:
the porosity of the soil and
the permeability of the rock.
Water can be temporarily stored via
interception. – in the storage of water
on leaf and plant stems.
12. all the water flowing over the drainage
basin’s surface is called runoff.
made up of streamflow - flow through
permanent river channels and
overland flow or surface runoff.
Overland flow - transfers water through the
basin either as:
sheetwash, across the surface, or
in tiny channels called rills.
Beneath the surface, water is transferred via
throughflow, which is the movement of water
through the lower soil towards rivers, and
groundwater flow (base flow).
Water that has been intercepted by foliage
may also be transferred, either directly as
throughfall, or by running down branches
and stems via stemflow.
13. final release of the water in a drainage basin
flow into the sea will be the main output of a
drainage basin.
Some water will also be lost via
evapotranspiration.
Evaporation from water bodies and soils
Transpiration from plants
