1. The Drainage Basin
as a system

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

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