Rivers and coasts .pptx

8/20/2019 Rivers and coasts .pptx

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Rivers and coasts


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eral erosional processes

These processes erode materialat the coast and in a river.

Hydraulic action

The force of thewater breaks rock

particles away fromthe river

channel/cli.

Corrasion/Abrasion

Eroded rocks rubagainst the

channel/thrownagainst the cliwearing it away.

Attrition

Eroded rockspicked up by the

river/wavessmash into each

other.

Corrosion/Solution

River/seadissolves sometypes of rock

such as chalk andlimestone.

Coastal erosion is aected by: The point at which the wave breaks teepness of the wave. Rock type and structure ! "hard rock

such as granite is far more resistant toerosion than soft rocks# such as clay$.


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ral transportation processes

These processes movematerial at the coast

and in a river.

mall particlesare carried

along by thewater.

%arge particleslike boulders arepushed along the

bottom of theriver bed/sea by

the force of thewater.

oluble materialsdissolve in waterand are carried

along.

&ebble si'edparticles are

bounced along theriver bed/sea by theforce of the water.


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pes of waves

Destructive

(estroys "takesbeach away$

trong backwash

)eak swash

Constructive

Creates "put sandon the beach$

trong swash )eak backwash

in*uenced by: how long the wind has been blowing the strength of the wind how far the wave has travelled "the

fetch$


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stal erosional landforms

Wave cut platform )eather weakens the top of

the cli.

The sea attacks the base ofthe cli forming a wave cut

notch.

The notch increases in si'ecausing the cli to collapse.

The backwash carries therubble back to the sea

forming a wave cutplatform.

The process repeats itselfand the cli continues to

retreat.

+

,

-


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Headland erosion

0ydraulic action createscracks in the headland.

1vertime the hydraulicaction causes the crack to

become deeper.

This creates a cave. Thismay eventually break

through.

This creates an arch. Thearch will eventually become

bigger and collapse.

This leaves a stack. 2orcesof erosion turn the stack into

a stump.

+

,

-


7/33Coastal erosional landformsCase study Swana!e" #ld Harry Roc$s


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Headlands and bays

The sea attacks an area ofcoast with alternating bands

of hard and soft rock.

The soft rock "sand or clay$are eroding more 3uickly.

This creates a bay.

The hard rock is moreresistant and takes longer to

erode.

This leaves a headland

4utting out to sea.

+

,

-


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stal depositional landforms

%eaches

Constructive waves help tobuild up beaches.

The soft rock "sand or

clay$ are eroding more3uickly.

This creates a bay.

The hard rock is moreresistant and takes longer

to erode.

+

,

-


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stal depositional landforms

SpitsLongshore drift moves

material along the coastline.

5 spit forms when thematerial is deposited.

1ver time# the spit growsand develops a hoo$ ifwind direction changes

further out.

)aves cannot get past aspit# which creates a

sheltered area where silt isdeposited and mud *ats or

salt marshes form.

+

,

-

5 bar forms when a spit 4oins to two headlands.

%ars


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Coastaldepositionallandforms

Case studyHurst Castle

spit


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astal mana!ement

Hard en!ineerin!

Rip!rap

6reakwater

7roynes

7abions

ea wall

Revetment

E8pensive 9nattractiv

e

%ong!term

6eachesremainnatural

Easilydestroyed

outh beachesa deprived ofsediment

6uild upthebeach

Cheap

Thebouldersare good atabsorbingwaveenergy

&reventserosion.

5cts as a*oodbarrier

E8pensive eed

maintaining Creates a strong

backwash

Caneasily bemoved

Theyneed to

bereplaced

Cheap

E;cient

Cagesrust

hortlifespan

E8pensiveCreates astrongbackwashwhich erodesunder thebarrier.

Theyabsorbthe waveenergy


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astal mana!ement

Soft en!ineerin!

6eachreplenishment

Createswiderbeaches.

&rotectsfromerosion and

*ooding %ooks

natural

Taking materialcan killorganisms


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y protect the coast'

ocial

Economic

Environmental

(eaths

)ater suppliesaected

%oss of housing

%oss of 4obs(amage to

infrastructure

%oss oftourism

2loods damage farmland

6usinesses on theedge

0ouse pricesfall


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Managed Retreat & conflict

Happisburgh, Norfolk

#ld &ana!ement (all)* years old+

!Revetments > nowdamaged "from a storm$

and not eective

!7roynes were placed tostop the rate of erosion#however they are not

helping enough.!Rock 5rmour > now little

eectiveness


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drolo!ical cycle

2lows!)ater

moving.

tores!)aterstored.


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aina!e basin The area of land a river gets its waterfrom.


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pper course

Waterfalls

nterloc$in! spurs

Created when the river *ows overan area of hard rock followed by

soft rock.

The soft rock is eroded more

3uickly creating a step.

5s the water goes over the step iteroded more and more of the

softer rock.

5 steep drop is created which iscalled a waterfall.

+

,

-

The hard rock is undercutby the erosion and

collapses.

The collapsed rock isswilled around and helpsto erode the softer rock

in the plunge pool.

1vertime more collapses

occur and the waterfallretreats creating a gorge.

F

The river eroded vertically downwardscreating G!shaped valleys.

The rivers are not powerful enough toerode laterally as they have to windaround the hillsides.


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iddle course

The current if faster on the outsideof the bend because the channel is

deeper.

Therefore more erosion takes placeon the river bend forming a river

cli.

The current is slower on the insideof the bend because the channel isshallower.

o eroded material is deposited onthe inside forming a slip!o slope.

+

,

-

Erosion causes the outside bendsto become closer and the riverbreaks through. (eposition cutso the meander forming an o8!

bow lake.

&eanders

#56bow la$e


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wer course

8lood plain7evees

%evees are natural embankments.

(uring a *ood eroded material isdeposited over the *ood plain.

The heaviest material is depositednearest the river channel.

1vertime the deposited material

builds up creating levees alongthe channel edge.

Deltas

River are forced to slow down

when they meet the sea or a lake.


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ong !rofile of a ri"er

Ri"er #ees - North East England

4pper Course!ource high in the &ennines

"BH-m above sea level$!0igh run o as steep G shaped

valleys of impermeable rock !0igh rainfall > good water

supply !=any tributaries

!2amous high fall waterfall >tallest in England ,+ metres high

!7orges# rapids and potholes at%ow force

&iddle Course6Clear widening and

meandering!=eanders cut o in the

+Hth century!ides become less steep

!%ateral erosion

7ower Course!Gery urbanised and large populations. Eg Iarn

!


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uses of ,oodin!

9hysical Human

4rbanisation9rban areas have lots ofimpermeable surfacessuch as tarmac. Thismeans the water runs othe surface 3uickly and tothe river.

Deforestation Trees intercept the rainwater. They also take up water. Cuttingdown the trees increasessurface!runo and therefore the

volume of water in the river.

Geolo!y


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,ood hydro!raph5 *ood hydrograph shows whether ariver has *ooded. The lag time shows

how 3uickly the water reached theriver.

)hen the river hasreached itscapacity.

)hen the river *ow

decreases.

)hen the river*ow increases.

The time it takesfor the water to

reach the river.

)hen therainfall is at its

highest.

The normal*ow of the

river.

d t


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od mana!ement(ams andreservoirs

Gery

e8pensive 2looding

downstream

tore

water 0ydroelectric power

2lowcontrol

Channelstraightening

=an!made levees

2lood warnings

&reparation

2lood plain 'oning

2loodingmayhappendownstream as watergets therefaster

)atermovesmore3uickly

Catastrophic *oodingif leveesbreak

Rivercan holdmorewater

Hard

en!ineerin!

Soften!ineerin

(on@t stop

the *ood %E(C lackof accessto radioetc

9rbane8pansionis limited

o help inplacesalready

built on

(oes notmeansafety

E8pensiveto modifybuildings

Risk of*oodingreduced


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ME$% lood

'oscastle 2(()

Reasons for the ,oodin!

9H:S3CA7!5 very wet 5ugust ", timesaverage rain$ 1 the ground

was already saturated

! rapid runo !Con*uence of Rivers Galency

J Kordan is 4ust above thevillage

!5 very high tide > made itdi;cult for water to *ow out

to sea

H4&A;!6ridges were low so acted aa dam ! debris such as tree

trunks caught on them waterpiled up until it burst through

in a great wave

!=any buildings J roads werepositioned close to the river

*cm +2ins of rain

fell in to hours

Very Short Lag Time

9rimary 3mpacts

- L cars# and caravanswere swept out to sea

- a wall of water sweptthrough the village

destroying everything inits path

- buildings were sweptaway

- =any other houses#

shops etc were *ooded#with mud L sewage as

well as waterMpossessions also ruined- Roads under ,.Fm of

water- o deaths# few serious

in4uries

Secondary 3mpacts- HN of economy dependent on tourism

O lost money O, accommodationproviders J tourist attractions/shops

forced to shut- encouraged to usemore *ood resistant material# raise height of

electrical wiring etc!Environment 5gency > *ood warning

system L information!Council runs special advice days#

encouraging people to have an emergencyevacuation

pack J to take out insurance. Council has

an emergency action plan.

ince , > *ooding again# still damagebut not as damaging as this event

%lear rescue and relief

argely economical impacts

60% f h k fl d d


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E$% lood

'angladesh 2(()

Characteristics of %an!ladesh

!%ays mainly on *oodplains# so *at land=ost of the land lies metres below sea!- main rivers! The 7anges#6rahmaputra and =eghna.!=onsoon season evey year > highconcentrated rainfall in a few months"Kune to eptember$.

!+#Bmm and ,#mm rain a year.!&overty is a huge issue in 6angladesh!low literacy rate!2looding occurs naturally in 6angladesh!now from the 0imalayas melts eachyear and increase river discharge!ediment blocks up the river andcauses *ooding!(eforestation in the forest increases

run o and reduces lag time!Cyclones occur in the 6ay of 6enegaland causes coastal *ooding!(ensely populated areas meaningincrease in deaths

The 2004 floods lasted from July to September

and covered 50% of the country at their peak.

Social impacts!- million people were

made homeless !&eople died as a resultof disease because theyhad no access to clean

water.!

roads# bridges# embankments#railway lines# irrigation systems

!5ll domestic and internal *ights hadto be suspended during Kuly

!Galue of damage was assessed asbeing in region of P,., billion of N

of total 7(& for ,

=nvironmentalimpacts

(uring Kuly and 5ugustappro8imately -BN of the

total land area was*ooded including

B# ha ofagricultural land and

(haka2loods caused river bank

erosion especially onembankment areas closeto the main channels# soil

erosion# water!logging#

water contamination

Response and mana!ement !Reliance on go support > Dnancial

and emergency supplies >9disaster management support!elf help schemes promoted

!local community early warningsystem implemented# plus shelters!


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!eo! oneeasy tack earns

medium 6each earns

hard 0ydraulic5ction

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!eo! oneeasy pit earns

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'onning

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meltearns

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Rivers and coasts .pptx

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