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Summary Ultimate Guide to CCEA Geography
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Providing an in-depth summary of all things Geography. Covering many themes throughout, this text has everything you need to know to ace your exam.
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Geography: Understanding Our Natural WorldTHEME A:RIVER ENVIRONMENTS
THE DRAINAGE BASIN:A COMPONENT OF THE WATER CYCLE
A drainage basin is the area of land that it drained by a river and its tributaries. When a
droplet of water falls onto the land (as precipitation), gravity will make sure that the water is
‘pulled’ downhill to return to the sea.
A major component of the water cycle is the drainage basin system.
There are many inter-relationships within this system:
Inputs: How water is introduced into the drainage basin system. This is known
as precipitation.
Stores: How water is stored or held for a period of time within the drainage basin
system - interception (by vegetation), soil moisture, surface storage (lakes),
groundwater
Transfers: A process or flow of water from one place to another in the drainage basin
system - surface run-off/overland flow, infiltration, percolation, through-
flow, groundwater flow
Outputs: How the water is released either back to the sea or back into the
atmosphere - river discharge, evapotranspiration
,Characteristics of the Drainage basin:
Drainage basin - the area of land drained by a river.
Catchment area - the area within the drainage basin.
Watershed - the edge of highland surrounding a drainage basin which marks the
boundary between two drainage basins.
Source - the beginning or start of a river.
Confluence - the point at which two rivers or streams join.
Tributary - a stream or smaller river which joins a larger stream or river.
Mouth - the point where the river comes to the end, usually when entering a sea.
How does a River change course Downstream?
A river changes shape as it flows from its source to its mouth. A section of the course of a
river drawn from source to mouth is known as a long profile.
Long profiles
, The source
of a river is
often in an
upland
area. Near
the source,
a river flows
over steep
slopes with
uneven
surfaces.
As a river
flows down
steep
slopes, the
water
performs ve
rtical erosion. This form of erosion cuts down towards the river bed and carves out steep-
sided V-shaped valleys.
As the river flows towards the mouth, the gradient of the slope becomes less steep.
Eventually the river will flow over flat land as it approaches the sea.
As the river moves from the source to the mouth – both the depth of the river and
the width of the river will both increase.
The load of a river will also change as it is transported and eroded along the river's profile.
As a result, the size and shape of stones will change as they journey through the river
profile.
The discharge will increase as the river approaches the sea.
The discharge is usually calculated as the cross-sectional area (depth x width) multiplied by
the velocity or speed of the water.
RIVER PROCESSES
Erosion, deposition and the different materials they carry all contribute to how rivers shape
surrounding land.
Erosion
Erosion involves the wearing away of rock and soil found along the river bed and banks.
, Erosion also involves the breaking down of the rock particles being carried downstream by
the river.
The four types of river erosion
Hydraulic action - the force of the river against the banks can cause air to be trapped
in cracks and crevices. The pressure weakens the banks and gradually wears it away.
Abrasion/Corrasion – the force of the water in the river carrying stones and other
materials grinds the bedload like a piece of sandpaper.
Attrition - rocks being carried by the river smash together and break into smaller,
smoother and rounder particles.
Solution/Corrosion - soluble particles are dissolved by weak acids in the water.
Transportation
Rivers pick up and carry material as they flow downstream.
Solution - minerals are dissolved in the water and carried along in solution (in the
water).
Suspension - fine light material is carried along in the flow of the water.
Saltation - small pebbles and stones are bounced along the river bed.
Traction - large boulders and rocks are rolled along the river bed.
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