Transcript The Work of Rivers

Ok 1 (U) notice anything?
Oh no Jackie
Its those
First Years
again!
First year geography
Ms Clifford
• Rivers: How they shape our land
Some important river
terms
• Source-where a river begins
• Course- the route it takes as it flows from an upland area
down through its valley until it enters the sea
• Tributary- a stream or river which joins a larger river
• Confluence- the point at which a tributary joins the river
• Mouth- the place where a river enters the sea
• Estuary- the part of the mouth that is tidal
• River basin- the area that is drained by a river or its
tributaries
• Watershed- the high ground that separates one river basin
from another
There are 3 stages in a rivers life
• The youthful stage (upper stage)
• The mature stage (middle stage)
• The old stage (lower stage)
3 stages of a rivers life…just like humans life!
The Work of Rivers
The erosional work of streams/rivers
carves and shapes the landscape through
which they flow.
3 functions of rivers
a. Erosion=wearing away the landscape
b. Transportation=moving the material
away (called the rivers load)
c. Deposition=to drop the load along the
way
The Work of Rivers
RIVERS MAY ERODE IN 4 WAYS:
1.
Hydraulic action
The force of the flow of the
moving water erodes pieces of rock
from the banks and bed of the river:
this is called Hydraulic Action
(This material is called the load)
The Work of Rivers
2. Abrasion
Load carried by a river will scrape
against the soil and rock along the bed
and banks of the river, deepening and
widening the river channel. This process
slowly wears the bed and banks away.
The Work of Rivers
3. Attrition
When rocks carried by the river rub
against each other they are worn down
and smoothed.
Attrition
The Work of Rivers
4. Solution
Certain minerals in rocks like limestone
can be dissolved by the river
The rate of erosion
depends on
• The size of the river- it erodes
faster when it is in flood
• The speed of the river- a fast
flowing river has more erosive powers
• The hardness of the rock- some
rocks erode more easily than others
How does the river
transport its load?
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It does this in 4 different ways:
Traction-rolling of stones
Saltation- bouncing of stones
Suspension- carrying of stones
Solution- the load is dissolved
4 ways it transports its
load
Deposition of a river
• This is the dropping of the rivers
load
The Work of Rivers
Rivers will deposit their load when:
a. They lose speed
b. There is a reduction in water in the rivers
channel
c. They flow into a lake or sea
d. The slope or gradient of the river is
reduced
The Work of Rivers
A river’s volume decreases when
• Dry season
• Dry region with high evaporation
• Presence of permeable rocks
• Receding flood waters
The Work of Rivers
A river’s speed decreases when
• It enters a lake
• It enters a calm sea
• It enters a gently sloping plain
3 stages of a river
• Youthful stage
• Mature stage
• Old stage
The youthful stage of a
river
• At this early stage of the river, it
flows down a steep gradient.
• The river has a small volume
• It cuts down into the rock by a
process known as vertical erosion
• It does this though hydraulic action,
abrasion, attrition or solution
Features /landforms of
the youthful stage
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V shaped valley
Interlocking spurs
Potholes
Waterfall
Yummy 
V Shaped Valley
V Shaped Valley
• V shaped valley have steep sides and
narrow floors. These are formed as the
river cuts down into its bed, deepening it
by “vertical erosion”. Meanwhile
weathering breaks up the soil and rock,
weakening the sides of the valley. They
eventually collapse and the debris falls
into the river. This gives it the v shape
Interlocking spurs
Interlocking spurs
• These are the areas of high ground that
jut out like a jig saw from each side of the
valley. If the river meets obstacles of
hard or resistant rock like granite-it is
unable to cut through it. Instead it flows
around them but still continues to erode
downwards. This is why the river develops
a zig-zag course
Potholes
• Potholes are circular-shaped hollows
found on the riverbed. When the
riverbed is uneven, the water begins
to swirl around. Pebbles that are
carried by the swirling water cut
down into the riverbed, creating
hollows called potholes. This is the
process of abrasion. Example: Liffey
Waterfalls
Waterfalls
• A waterfall is a feature where the water flows or falls over
a vertical slope.
• It develops where a band of hard or resistant rock lies on
top of a band of soft rock. The softer rock is eroded by
the river more quickly than the hard rock. This causes a
plunge pool to be formed by the force of the falling water.
• The falling water also cuts under the waterfall to form an
over-hang, which eventually collapses.
• As this process repeats itself-the river gradually retreats
upstream
• Examples-Powerscourt, Glencar waterfall or Torc waterfall
The mature stage of a
river
• The river has a greater volume since
many tributaries have joined it. It
flows over a gentler gradient.
• It has a larger load of material to
carry now
• It flows more slowly than the
youthful stage
3 features/landforms of
a mature river
• Wider valley troughs
• Meanders
• Flood plain
Wider valley troughs
• The sides of the mature valley are less
steep and the floor is wider and flat
• Lateral erosion widens the valley
• The river swings from side to side,
removing the interlocking spurs
• Weathering and mass movement continues
so the valley becomes less steep
Meanders
Meanders
• Meanders are curves or loops that develop along the course
of a river.
• They are formed by both erosion and deposition.
• As the river flows around a slight bend, the water on the
outside bank flows more quickly and erodes the bank.
• The water on the inside flows more slowly . As a result, it
deposits its load.
• This process continues and the meanders become more
pronounced.
• Examples include Shannon, Blackwater and the Moy
meander
Flood Plain
Flood plain
Floodplain
• This is the land on either side of the river.
It has a very covering of fertile clay called
alluvium.
• Following a period of heavy rainfall, the
size of a river increases and it may
overflow its banks to flood the land.
• The water loses its speed and deposits a
layer of alluvium
Old rivers
• This is the last stage of the river and
it flows slowly with little energy. It
deposits its load because of this lack
of energy and because the load is too
heavy.
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Features found at the old stage include:
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Ox Bow lakes
Levees
Deltas
Ox Bow Lakes
How an OX BOW Lake is formed
• An ox bow lake is a horse-shoe shaped lake that
was once part of a meander
• Erosion takes place on the outer banks of the
river and in between the neck of 2 meanders
• When the energy has a lot of energy it cuts
through the neck to flow along a straight path
• The river has little energy so it deposits its load
along the channel
• This eventually cuts off the meander to form an
ox bow lake
Ox bow lake
Levees
levees
• Levees are raised banks of alluvium
• When a river bursts its banks, it flows over the
floodplain
• It quickly loses its energy and deposits its heavier
load close to the river
• Smaller rocks/stones are carried further away
• Over time the rocks build up along the river banks
to form levees
Deltas
delta
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How a delta is formed
A delta is formed when a river is about to enter
the sea.
The river loses speed and deposits its load.
Lighter material can be carried out to sea but the
heavier load is deposited at the mouth of the
river.
Over time the deposited rocks build up forming
new land called deltas
The river is split into smaller channels called
distributaries
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not all rivers flow into the sea so there will be no delta 
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`v
River mississippi
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The mississippi drains nearly 40% of the land surface of the USA
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Over time man has interfered with the river in the following ways:
(A) building man made levees to prevent flooding
(B) cutting off meanders so the river flows straighter
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THIS HAS EFFECTED THE RIVER IN MANY WAYS:
(a) levees have walls 8 metres high. The river cannot overflow its
banks and deposit its load so instead the level of the river
increases
The authorities built the levee walls even higher and this means
that the river is now higher than the landscape
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Learning outcome
Floods (positives and negatives)
Dam building and hydro electric power
Quick pop quiz
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3 stages of rivers?
Source?Tributary?
Confluence?
Rivers erode in 4
way?
• Rivers transports
in 4 ways?
• Rivers overflow
leaving deposits of
----------• At which stage of
a river is a
waterfall found?
The flood of 2001
A example of the Mississippi flooding
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In spring of 2001, many areas received three times the normal
amount of rainfall
As the snow on the mountains melted, it fed the river mississippi,
raising the level of the river
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The river became so swollen, it broke some of the levees and
flowed across the floodplains
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What were the effects of the flooding?
Factories, houses, shops and businesses were flooded
60 people died
Crops were ruined and many animals were killed
Water supply and sewage systems were disrupted
Ships could not travel along the mississippi so this had economic
consequences
How can rivers be useful to man?
• Rivers provide excellent settlement sites for man. Many
cities such as Dublin are built alongside the river Liffey
• The river is a source of food and water.
• Rivers are a means of transport: the river Rhine in Germany
is used by barges to transport goods such as coal. This
reduces traffic congestion on the roads
• Rivers provide us with rich agricultural land
• Rivers can be used to provide hydro electric power (HEP)
• Rivers are also used for leisure activities such as……
What are the negative effects of rivers?
• When rivers flood, it can cause death and destruction to
farmland and property
• Rivers can become polluted by man and this damages aquatic
life.
• For example: When farmers spread fertiliser or use
pesticides on slopes (hills) when it rains, this runs down the
hill and finds its way into rivers.
Dam building
• A dam is a barrier constructed across a river to control the
flow of the river
• There are many advantages to dam building:
• (1) hydro electicity power stations are built near the river
and they use the energy from the water by converting it
into electricity
• (2) artificial lakes called reservoirs are built behind the
dam and this water can be used as local water supply or for
leisure activities
• There are many disadvantages to dam building:
• Sometimes as the level of water rises, areas are flooded
and this means that homes are destroyed and agricultural
land is lost
• People have to relocate away from the dam
• Fish farming can be effected due to the loss of spawning
ground
Poulaphouca dam
Hydro electric power station
How is electricity created using water??
• The theory is to build a dam on a large river that has a large
drop in elevation.
• The dam stores lots of water behind it in the reservoir.
Near the bottom of the dam wall there is the water intake.
• Gravity causes it to fall through the penstock inside the
dam.
• At the end of the penstock there is a turbine propeller,
which is turned by the moving water.
• The shaft from the turbine goes up into the generator,
which produces the power.
• Power lines are connected to the generator that carry
electricity to your home and mine.
• The water continues past the propeller through the tailrace
into the river past the dam. By the way, it is not a good idea
to be playing in the water right below a dam when water is
released!