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Oh no JackieIts thoseFirst Years again!

First year geographyMs 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?

• 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

• 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.

• Features found at the old stage include:

• 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

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

• not all rivers flow into the sea so there will be no delta • `v

River mississippi• The mississippi drains nearly 40% of the land surface of the

USA

• 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

• 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

Learning outcomeLearning outcomeLearning outcomeLearning outcome

Floods (positives and negatives)Floods (positives and negatives)

Dam building and hydro electric powerDam building and hydro electric power

Quick pop quiz• 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 2001A example of the Mississippi flooding

• 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

• The river became so swollen, it broke some of the levees and flowed across the floodplains

• 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!