1.1 Hydraulic action - Force of the river against the banks
can cause air to get trapped in cracks and crevices.The
pressure weakens the banks and gradually wears it
1.2 Attrition - rocks being carried by the river
smash together and break into smaller,
smoother and rounder particles.
1.3 Corrosion - acids in the
water eat away at certain types of
rock (soft less resistant) e.g
1.4 Abrasion - rocks carried
along by the river can
wear down the river bed
2.1 Solution - minerals are dissolved in the
water and carried along in solution.
2.2 Suspension - fine light
material is carried along in the
2.3 Saltation - small pebbles and stones are
bounced along the river bed.
2.4 Traction - large boulders and
rocks are rolled along the
3 River Profiles
3.1 Upper Course
3.1.1 Long Profile - A river is steeper towards
the source of the river as it is often found
in mountainous areas.
3.1.2 Cross profile - in the upper course a river tends to be quite narrow and
shallow. The bottom and sides tend to be littered with many large angular
rocks, causing a lot of friction for the water flowing past them,so creates a
lot of turbulence and friction.This slows the water down as it uses its
energy to overcome friction - in the upper course a river is flowing at its
slowest velocity. valley sides are steep and v-shaped as there is lots of
vertical erosion. There is lots of vertical erosion because the large angular
rocks and boulders are transported down the river by traction, this grinds
away at the river bed through abrasion.The transportation of this material
is aided by the force of gravity and the amount of energy the water has
because of gravity as the gradient of the river is steep.
3.2 Middle Course
3.2.1 Long Profile - the gradient of a river becomes less steep
further towards the mouth of a river as the land begins to
level off and the river erodes towards its base level.
3.2.2 Cross Profile - a river increases in width and
becomes more u-shaped because there is more lateral
erosion,it also increases in depth as some vertical
erosion still takes place.
3.3 Lower Course
3.3.1 Long Profile - lower part of a river has the greatest cross section, highest
hydraulic radius, greatest velocity (because of decrease in chanel bed
roughness) and discharge.The gradient of the river is smaller as the river
approaches the sea or lake where the land is much flatter.
3.3.2 Cross profile - velocity and energy increasses due to increased discharge.The river
performes more lateral erosion making the chanel wider and smoother. As a result
there is less turbulence and friction, making the flow more efficient. At this stage the
water is flowing at its fastest and the river is deep in places where the water is flowing
3.4 Long profile - on a graph of the long profile of a
river there will be 'notches'/irregularities in the line.
These could be because of changes in rock type, sea
level or natural features like waterfalls in the upper
course of a river.
4 The Bradshaw Model
4.1 Average Velocity - Chanel bed roughness
decreases further downstream so the river
does not require to use its energy to
overcome friction like it does in the upper
course (its more efficient). For this reason
the velocity increases as the river maintains
4.2 Channel Depth - This increases as some vertical erosion still continues in the
middle course and hydraulic action and abrasion on the outside bend of
meanders causes parts of a river to become deeper. The channel depth is most
affected because increased erosion of particles means tht there is a lot more river
bed exposed so erosion of the river bed through hydraulic action occurs more
4.3 Load Particle Size - Most rocks and pebbles come from the source
of the river when they fall.As they move downstream they become
more and more eroded by attrition and corrosion so their size is
reduced.When there is low flow particles are stored on banks so
they can be broken down by weathering (particularly freeze-thaw)
but this depends on how long they are stored.
4.4 Discharge - discharge increases
largely further downstream as
more streams and tributaries join
the river and if there is a confluence of two rivers.
4.5 Occupied Channel Width - channel width increases
as more lateral erosion takes place downstream
unlike upstream where erosion is predominantly
4.6 Gradient - This decreases downstream because the land
levels out as the river travels further towards the sea from the
source which is in mountainous areas; the lower course is in
flood plains and the mouth may be in deltas.
4.7 Load Quantity - A river gets wider and deeper downstream, so it
has a larger capacity to hold more material.Through
transportation large rocks tend to break apart into smaller rocks
through attrition so the overall amount of particles in the river
4.8 Channel Bed Roughness - This decreases as you go
downstream because rocks have been eroded as they
travelled, so they are smaller and smoother.
5 River Course Features
5.1 Lower Course
5.1.1 Levees-Levees are natural embankments along the banks of a river.Rivers
can carry a lot of material so when a river floods it carries the material with
it.The water immediately loses velocity so heavy material is dropped first on the
edge of a river as it does not have enough energy to carry it. Lighter material
is transported further as less energy is required to carry it.When flooding
occurs again the banks get higher and higher;people sometimes build these even
higher to reduce the risk of flooding.
5.1.2 Floodplains - A floodplain is a wide, flat area of land either side
of a river in its lowercourse.It is formed by both erosion and
deposition.Lateral erosion is caused by meanders eroding the
outside of their bends-this makes the valley floor wide and flat.
When the river floods,the flood water spreads out on the valley
floor,slows down and deposits sediments it was carrying;This can
be beneficial for farmers because it can help fertilise the soil.
5.2 Middle course
5.2.1 Meanders - A meander is a bend in a riveri n
the middle course.In this section the river
flows faster as the bed is smoother so there is
less friction.Water flows faster on the outside
of the river bend.Hydraulic action and
abrasion undercuts the river bank and creates
a river cliff.The water flows slowly aroun the
inside of the river bend so it cant carry a lot of
material so deposits it.This is called a slip off
5.2.2 Oxbow Lakes - An oxbow lake occurs on the bend of a
river.Water erodes the the outside bend of a river
through hydraulic action an abrasion and deposits
sand/silt on the inside.The neck of the meander gets
closer together and eventually (normally when a river
floods) it pushes through the neck to follow the
shortest course.The old bend is abandoned by the river
and gradually dries up.
5.3 Upper Course
5.3.1 Waterfall - When a river meets a band of less resistant softer rock,hydraulic action and abrasion causes
the rock to erode, causing a undercutting.Because the underlying softer rock erodes more quickly
than the more resistant rock.The unsupported more resistant rock overhangs,becomes unstable through the
force of gravity and eventually collapses onto the river bed.This and other rocks causes abrasion of the river
bed.Hydraulic action also helps to create a deep plunge pool.This process is repeated so the waterfall
retreats upstream and overtime a steep sided river valley (gorge) is formed.
5.3.2 Interlocking Spurs - Streams that flow down steep valley sides into the river perform
vertical erosion so the sides of the tributaries and streams protrude outwards.The bed is
littered with rocks and debris which are occasionally after storms.This material wears
down the bed by abrasion as it is transported by traction and saltation.Areas of the
landscape that the river flows through contains hard rock , this means that the river
erodes these areas much more slowly than the softer rock.this means that the river
winds and bends as interlocking spurs are created. interlocking spurs are kind of like
the interlocking parts of a zip. when a river runs over alternating layers of hard and soft
rock,rapids and waterfalls may form.
6 Weathering - The breakdown of rocks and
minerals by physical and chemical
processes.This involves little/no
movement of material unlike erosion.
6.1 Physical Weathering (Freeze - thaw) - This happenes when
rainwater enters a crack or gap in a rock and freezes when
temperatures fall below 0 degrees.The water expands as it turns into
ice and experts pressure on the rock.This is repeated overtime so
eventually the rock cracks into smaller pieces.
6.2 Chemical Weathering - When rain water is slightly acidic (acid
rain) it can react with weak minerals within the rock causing them
to dissolve and the rock to decay and wear away.This can happen
if the air polluted by factory /vehicle emissions,acidic rain usually
occurs close to areas where there is lots of these emissions.
6.3 Biological Weathering - The roots of plants can
grow into cracks in a rock and split the rock appart.
7 River Valleys
7.1 Weathering and Mass Movement - Weathering
causes the valley sides to break down which
allows mass movement - The weathered material is
transported down the valley sides to the river, via
rockfall or sliding where it becomes part of the
7.2 Gorges- Gorges have near vertical sides because there is little weathering or
mass movement,the river cuts downwards rapidly;perhaps the land is being
lifted up too.in different conditions the valley might be wider because
weathering and mass movement operate fast,as in a tropical climate,rivers
7.3 Geology - where a river flows over hard resistant rock the valley sides
tend to be steep and the sediment load is small because erosion is
slow.When a river flows over bands of softer less resistant rock the
valley sides tend to be gentile and the sediment load is too large because
erosion is rapid.
7.4 Factors That Affect the Shape
of River Valleys
7.4.1 The speed of weathering;if
scree piles up, weathering
rapidly takes place.
7.4.2 The speed of mass
7.4.3 How quickly the river can remove the
material brought by mass movement.
7.4.4 If the river has plenty of energy, it takes the
material away and uses it to help erode the
valley making it steeper (abrasion)
8 Key Terms
8.1 Rock Outcrops - exposures of bedrock above the
surface of the ground.
8.2 Scree - accumulated
below a crag or
other exposed rock
will accumulate at
the base of the
scree, carried by
8.3 Mass Movement - the movement of broken (weathered)
rock,minerals,soil and vegetation from steep valley sides to a river as a
result of the force of gravity. e.g. Weathering takes place on valley
sides, usually making it less steep overtime as material is moved from
the top of a slope to the bottom. However the river itself erodes its own
channel by wearing away the bed and banks as well as eroding the
base of the valley side, making it steeper and leading to mass
8.4 Landslides - Landslids occur when a hill or mountainside becomes unstable because of factors such as
erosion;this can overly steepen slopes.Earthquakes can cause landslides because they cause soil to move - on
steep slopes these soil slips cause landslides.When steep slopes become saturated with repeated heavy
rainfall landslides can occur, especially if there is no root support.Human actions can enhance the lack of root
support through deforestation.This stops water from being able to be absorbed by the roots so hillsides become
8.5 Soil Creep - Individual particles of soil
slowly move down valley sides because
of gravity and collect at the bottom of
the valley sides.
8.6 Slumping - This happens when the bottom of a valley
side is eroded by the river.This makes the slope steeper
and the valley side material can slide downwards in a
rotational manner, often triggered by saturation due to
rainfall, which both 'lubricates' and makes it much
9.1 Factors That Encourage Flooding
9.1.1 A Steep -Sided Channel - a
river channel surrounded by
steep slopes causes fast
9.1.2 Lack of Vegetation or woodland - trees and plants
intercept precipitation (they can catch or absorb
water).If there is little vegetation in the drainage
basin then surface run-off will be high.
9.1.3 Drainage basin, consisting mainly of
impermeable rock - this will mean that
water cannot percolate (pass through)
through the rock layer, and so run
faster over the surface.
9.1.4 A Drainage Basin in an Urban Area - these consist
largely of impermeably concrete, which encourages
overland flow.Drains and sewers takes water quickly and
directly to the river channel.Houses with sloping roofs
further increase the amount of run-off.
9.2 A flood ocurs when a river breaks its banks and
water spills onto the flood plain.Tthe faster the
water from hesvy rsinfsll reaches the river chsnnel
the more likely the river is to flood.
9.3 Flood Management -
techniques often involve
lengthening the amount
of time it takes for water
to reach the river
channel, so increasing
the lag time.
9.3.1 Hard-Engineering Options V.s
Soft-Engineering options - hard options tend
to be more expensive and have a greater effect
on the river and surrounding landscape.soft -
engineering options are more ecologically
sensitive. Effective flood management should
be economically,environmentally and socially
sustainable.Sustainable strategies allow
management without compromising the needs
of future generations
220.127.116.11 Hard-Engineering Options
18.104.22.168.1 Dam Construction -Dams are often built along the course of a river in order
to control the amount of discharge.Water is held back by the dam and
released in a controlled way.This controls flooding.Water is usually stored
in a reservoir behind he dam.This water can then be used to generate
hydroelectric power or for regeneration purposes. Building a dam can be
very expensive .Sediment is oftentrapped behind the wall of the
dam,leading to erosion further downstream.Settlements and agricultural
land may be lost when a river valley is flooded to form a reservoir.
22.214.171.124.2 River Engineering - The river channel may be widened or
deepened allowing it to carry more water.A river channel may be
straightened so that water can travel faster along the course.The
channel course of a river can also be altered diverting flood water
away from settlements.Altering the river channel may lead to a
grater risk of flooding downstream as the water is carried there
126.96.36.199 Soft-Engineering Options
188.8.131.52.1 Afforestation - trees are planted near to the river so there is a greater
interception of rainwater and lower river discharge.This is a relatively
low cost option which enhances the environmental quality of the
184.108.40.206.2 Managed flooding - the river is allowed to flood naturally in places, to
prevent flooding in other areas i.e. near settlements.
220.127.116.11.3 Planning - local authorities andnational governments intraduce policies
to control urban development close to or on the flood plain.This reduces
the chance of flooding and the damage to property. There can be
resistance to development restrictions in areas where there is a shortage
of housing.Enforcing planning regulations and controls may be harder in
9.3.2 Different interest groups have
different views about flood
18.104.22.168 Governments and developers prefer
large, hard engineering options
because by building a dam you can
generate income as profits can be
22.214.171.124 Environmental groups and local residents
often prefer softer options as they cause
little damage to the environment and do not
involve resettlement of communities.
9.4 The Impact of Flooding
9.4.1 Floods can cause damage to homes and possessions as
well as disruption to communications. However flooding can
have positive impacts on an area - flooding deposits fine silt
(alluvium) on to the floodplain making it very fertile and
excellent for agriculture.People living on or near to
flood[plains may rely upon regular flooding to help support
their farming and therefore provide food.
9.4.2 LEDC's tend to be more affected by
the effects of flooding more than
MEDC's.This is partly because LEDC's
have more farms, and farming
communities are attracted to fertile
floodplains LEDC's often do not have
the resources to prevent flooding or
deal with the aftermath of flooding.
10 River Background
10.1 The Hydrological Cycle - seas and oceans contain
97% of the world's water, and ice holds 2%.That leavs
just 1% of the world's water as fresh water on land or
in the air .This water is ecycled again and again
through the process of evaporation ,condensation
and water transfers such as surface run-off.
10.1.2 Key Definitions
10.1.2.1 Precipitation - Rain,snow, sleet or hail that falls on the ground.
10.1.2.1.1 Interception - when tree leaves and branches 'catch' precipitation and stop it from reaching
10.1.2.1.1.1 Evaporation - when water is turned from a liquid to a gas.
10.1.2.1.1.1.1 Transpiration - when water is lost from the leaves through water vapour.
10.1.2.1.126.96.36.199 Infiltration - when surface water soaks into the soil.
10.1.2.1.188.8.131.52.1 Soil moisture - when water is stored in the soil.
10.1.2.1.184.108.40.206.1.1 Surface storage - when water is stored on the Earth's surface (puddles).
10.1.2.1.220.127.116.11.1.1.1 Percolation - when water moves through permeable rocks .
10.1.2.1.18.104.22.168.22.214.171.124 Groundwater - when water is stored in rocks underground.
10.1.2.1.126.96.36.199.188.8.131.52.1 Through-flow - when water flows through the soil.
10.1.2.1.184.108.40.206.220.127.116.11.1.1 Groundwater flow - when water flows in rivers in rock underground.
10.1.2.1.18.104.22.168.22.214.171.124.1.1.1 Surface run-off - when water flows over the surface of the Earth.
10.1.2.1.126.96.36.199.188.8.131.52.184.108.40.206 River channel - when water flows in the river channel.
10.2 Terminology For The Study of Rivers
10.2.2 Drainage basin - the area of land drained by a river.
10.2.2.1 Catchment area - the area within a drainage basin.
10.2.2.1.1 Watershed - the edge of highland surrounding a drainage basin.It
marks the boundary between two drainage basins.
10.2.2.1.1.1 Source - the beginning or start of a river.
10.2.2.1.1.1.1 Confluence - the point at which two rivers or streams join.
10.2.3 Tributary - a stream or smaller rive
which joins a larger stream or river
10.2.3.1 Mouth - the point where the river comes to the end,
usually when entering a sea.