Hydrosphere - course notes.doc

8/9/2019 Hydrosphere - course notes.doc

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Hydrosphere – Course notes

You should be able to draw a diagram of the hydrological cycle and

describe the main elements of the diagram.

The H.C. is a closed system in that the amount of water that is contained

in the system remains constant. The system is powered by energy from

the sun.

The Drainage Basin

Drainage basins are part of the global hydrological cycle.

A drainage basin is an area of land drained by a river and its

tributaries.

Unlike the closed system of the hydrological cycle, the drainage basin

system is open. It has inputs, stores, flows and outputs.

The boundary of a drainage basin is called a watershed. This is usually

found on higher ground.

Advection

GeothermalEnergy

EmittedEnergy

SolarEnergy

Precipitation (23%)

Evapotranspiration (16%)Rn o!

"n#ltration

Rn o!

$atertale

&ceanStorage('%)

lods(*+**1%)

,ondaryo- system

"cestorage

(2%)

Grond.aterstorage (1%)

SoilSoil Soil

Rivers /0aes (*+*1%)

Precipitation

(%)Evaporatio

n(%)

4he Gloal 5ydrological ycle


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The definitions for all these words are on pages 47 and 48 of the

Core Higher eography te!t boo".

The precipitation that falls in a drainage basin is sometimes intercepted

by egetation. If this happens then the rain water will take longer to

reach the ground as it trickles and flows down the leaes and branches of

the tree !stem flow". #nce the rain water reaches the ground and it is

i#per#eable then it will flow directly oer the surface back into the

rier !run off".

There could be many reasons why the ground is impermeable, these could

include it being made up of an impermeable rock !e.g. granite" or it may

already be saturated with water, alternatiely it may be coered with

tarmac in a town or city. $ll these factors would encourage water to

%uickly run oer the surface into the rier and could increase the risk of

flooding.

&ain water can soak into the ground if it is permeable. In this case water

trickles down through the top soil !infiltration" and eentually back to the

rier as through flow. 'ometimes water is held deep down in the bedrock

and ery slowly makes its way back to the rier although this may take

hundreds of years. This is called ground water. In such cases riers which

are fed mainly by through flow and ground flow hae a far smaller risk of

flooding as the water makes it way back to the rier channel in a slow,

gradual process.

Precipitation

"nterception yvegetation

Sr-ace Storage

"n#ltration

SoiloistrePercolatio

nGrond.at

er

4ranspiration

Sr-ace rno!(overland

7o.)

Evaporation

River carrying.ater to theocean8sea

4hrogh7o.

Grond.ater

7o.

$ater tale

9nsatratedroc8soil

Satratedroc8soil

"npt

Storage:lo.(trans-er)&tpt

Key

Stem 7o.


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The $or" of %ivers

There are three main processes in the way that a rier (works). These

are*

&. 'rosion

(. Transportation

). Deposition

&. 'rosion

The amount of erosion a rier can achiee depends on its energy or

discharge. $ rier)s energy increases with its olume, elocity and regime

!seasonal flow".

+rosion in a rier is caused by processes*

Attrition - when boulders, rocks and pebbles crash in to each

other and bits break off therefore being rounded and

reduced in sie.

Corrasion * Abrasion- the wearing away of the rier bed and

the banks by the rier)s load. This is the main method of

erosion.

Hydrauli+ A+tion - the sheer force of the rier breaks off

particles from the rier bed and banks. Corrosion ,Che#i+al -olution - dissoling of minerals from

the rocks.

$ rier)s alley is deepened by verti+al erosion - entirely a rier process.

$ rier)s alley is widened by lateral erosion - affected by weathering on

the alley sides and by the rier on the rier banks.

(. Transportation

$ rier transports its load in ways*

Tra+tion - dragging of pebbles, grael along its bed.

-altation - bouncing of the load.

-uspension - light sediments of silt and clay are held in

suspension by the rier)s turbulence !the greater the

turbulence, the greater the sie of particles which can be

held". -olution - chemicals are dissoled in the water.


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). Deposition

'ediments are transported by a rier until it has insufficient energy to

moe them further and deposition takes place.

$ rier may lose its energy where*

There is a decrease in gradient.

There is widening or meandering of its channel.

There is an increase in load.

A Typi+al %iver profile !'/$ - e0am paper"

You need to be able to e0plain the changes along the course of a rier in

terms of these 1 main processes.

$n (ideal rier) is diided into three sections - the Upper, 2iddle and

3ower courses.

These courses all hae characteristic features which form the rierlandscapes.


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The /pper Course

Channel shape

The upper stretches of a rier are rocky, often being coered

with boulders of different shapes and sies. The rier channelis usually narrow and fairly straight.

0alley

features

The alley is a 45shape in the upper course, meaning it is ery

narrow.

1ain pro+esses

$s the rier is fast flowing it has a high amount of energy to

erode. This erosion usually happens ertically as the rier bed

cuts down into the alley floor. The main types of erosion

operating in this stage of the rier are hydraulic action and

corrosion, due to the fast flowing nature of the water. 6otholes

form where pebbles and cobbles, rotated by swirling eddies,

grind deep holes in the bedrock.

radient

The gradient is usually ery steep in the early stages causing

the rier to be fast flowing. This encourages the main work of

the rier to be erosion.

Dis+harge Under normal conditions the discharge is fairly low.

%ivers load

7oulders of arying shapes sies occupy the rier bed. 3arge

stones and rocks trael down the rier channel by traction andsaltation.

2eatures you

need to learn

8aterfalls, gorges, 45shape alleys, Interlocking 'purs,

potholes.

$aterfalls

Usually found where there are

differences in rock hardness. $ fast

flowing rier has a large amount ofenergy to erode ertically. The soft

rock is eroded faster than the hard

rock, usually through the process of

corrasion and hydraulic action, !e0plain the meaning of these processes in an e0am answer" creating a step in the landscape.

#er time the rier will undercut the

hard rock creating an oerhang. This

oerhang of hard rock is no longer supported and eentually breaksoff and collapses in to the rier below. This hard rock is then swirled


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around at the base of the waterfall and helps to

care out a deep plunge pool. $s this process repeats

itself time and again the waterfall gradually

retreats back up the alley leaing a steep sided

gorge in its wake.Corrieshalloch Gorge

(Source: www.panoramio.com/photos/original/1217468.jpg )

03-hape 0alleys

9. 4ertical erosion !in the form of

abrasion, hydraulic action and

solution" in the rier channel results in

the formation of a steep sided alley.

(. #er time the sides of this alley

are weakened by weathering

processes and continued ertical

erosion at the base of the alley.

). :radually mass moement of materials occurs down the alley

sides, gradually creating the distinctie 5shape.

4. This material is then gradually transported away by the rier

when there is enough energy to do so.!'ource*

http*;;geobytesgcse.blogspot.com"

3

H a r d e r , m o r e r e s i s t a n t r o c k

Waterfallretreatsupstream

;Gorge-like sidesdevelop as waterfallretreats upstream

2 Overhang develops and

collapses whenunsupported

Rivercontines

do.nstreamAngular,fallenrocks

Softer, lessresistant rock,which is erodedmore uickly,which leads to -

1 !ndercutting

"eep plunge pool# "eepened $yhydraulic action and a$rasion of fallen,angular rocks, which are swirled at times of

high discharge % deepening the pool#

V-shape valley with interlocking spurs.www.bws.wilts.sch.uk/.../Geog/geography.html

http://www.panoramio.com/photos/original/1217468.jpghttp://www.panoramio.com/photos/original/1217468.jpghttp://www.bws.wilts.sch.uk/curriculum/departments/Geog/geography.htmlhttp://www.panoramio.com/photos/original/1217468.jpghttp://www.bws.wilts.sch.uk/curriculum/departments/Geog/geography.html


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otholes

$ pothole is formed in the rier bed when boulders

are too heay to be carried along with the rier

therefore they ches of slow moing water.

• &ifles = shallower sections of faster water

www.winona.edu/Geology/MRW/LateProterozoic.htm

http://www.winona.edu/Geology/MRW/LateProterozoic.htmhttp://www.winona.edu/Geology/MRW/LateProterozoic.htm


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?. This causes the

water to deelop a

side to side swing.

1. The process is

assisted by erosion

and deposition.

. In the pools the rier currents start undercutting the rier cliffs.

This happens on the outside of the rier bend where elocity is

fastest.

#n the other side where the current is weakest deposition takes place

to form a rier beach or point bar.

@. 2eander formation is assisted by helicoidal flow of water. This is a

corkscrew like moement. This causes the meander to migrate down

stream.

A ,

ar) -orms also called a slip>o! slope+

0argest material deposited on pstream side+

Erosion on otside o- end(concave an) y hydralicaction and corrasion+ 4his is.here velocity isgreatest and -riction is minimal+River cli! develops+

Ri?e

Pool


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• Cross -e+tion A 3 B

The 5ower Course

Channel shapeThe channel is now at its broadest and deepest.

0alley

features

Due to lateral erosion alley sides may be seeral kilometres

away. The alley is dominated by wide floodplains.

1ain pro+esses Deposition is now the dominant process particularly duringfloods when the riers load is spread out oer the alley floor.

radientThe gradient is now ery gentle and in some cases may appear

totally flat. This encourages deposition to take place.

Dis+harge The discharge of the rier is at its greatest as large olumes

of water pour out into the sea.

%ivers loadThe rier)s load is carried entirely in suspension and solution

consisting mainly of fine sediments.

2eatures you

need to learn

Aloodplains, leees, braiding, o05bow lakes, deltas, rier

terraces !re


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2loodplains and 5evees #er many years, the rier has coered the alley floor with

enormous %uantities of alluium !sedimentary deposits". It was

deposited by migrating meanders and floodwater. $cross the

resulting leel floodplain, ariations in relief are ery slight so thatany rapid increase in discharge almost ineitably results in flooding.

8hen a rier floods, the floodwater)s speed reduces most %uickly

at the sides of the channel. Conse%uently coarser alluial

sediments are deposited at the channel edge, gradually building up

into natural ridges or leees. #ccasionally leees act as natural

embankments and often they hae been strengthened by man as a

part of flood preention measures.

Braiding Aor short periods of the year, some riers carry a ery high load in

relation to their elocity. 8hen a rier)s elocity falls rapidly, the

channel may become choked with material, causing the rier to

braid i.e. the channel splits up into seeral smaller channels which

flow around fresh (islands) of deposited material before re


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6!3bow 5a"e

In an e0am when e0plaining how o05bow lakes are formed it is important

to first e0plain how meanders deelop in a rier.

• $s can be seen in the diagrams below the neck of the meander

becomes narrower.

• During flood conditions the rier breaks through the neck of the

meander.

&=>o.laes


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• The fastest flowing current is now flowing in a straight line.

• The water in the meander rapidly loses energy and therefore

deposits material, this seals off the meander from the main

channel.

Erosion on concave ans gradally narro.ing the nec o-land

River eventally reas throghnec o- land sally at times o-7ood

o!

t>o! -ormed


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• The o05 bow lake may eentually dry up.

'stuaries and Deltas

8hen a rier enters a loch or the sea elocity is reduced and load

is deposited.

8here the rier)s mouth broadens to form an estuary, tidal

currents are able to scour out most of the sediments, transferring

them to the sea)s transportation system. The sediment that is not

remoed from the estuary forms e0tensie sand and mud banks,

often colonised by salt5tolerant egetation and e0posed at low tide.

Deltas are essentially the seaward e0tension of the floodplain and

form when tides are weak. They also grow where streams enter

freshwater lochs.

Distributaries are the small streams which hae formed due to braiding inthe rier channel.

Terra+es

&=>o. lae

o!

River 7o.s in ne.@straight channel

'ource* 8ikipedia


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$ rier terrace is a remnant of a former floodplain, which after

re


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If a rier is re


16/21

%e+ognising features on an 6.- #ap

The following is an e0ample of an answer. The map is diided into a

number of sections, howeer, if you would prefer to follow the whole map,

you should be able to borrow the map from the :eography department.

The map is the Thirlmere map.

The uestion is 3

9/sing appropriate grid referen+es: des+ribe the physi+al

+hara+teristi+s of the %iver Derwent and its valley fro# ();&


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Here, the rier flows along the

8est side of the alley in almost a

straight line hugging the base of

the alley side. $ number of

tributaries flow down and


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%iver Hydrographs

$ hydrograph is a record of channel flow in a stream or

rier.

It shows ariations in discharge with time.

$ Hydrograph has a number of main characteristics*

6recipitation - shown as a bar graph but sometimes not

always shown

7ase Alow - flow supplied by groundwater. This is a slowmoement therefore base flow rises slower and later.

/uickflow;'torm Alow - flow supplied by oerland flow and

soil throughflow. This gies the peak flows.

&ising 3imb - includes !a" rainwater that fell into stream

!b" water flowing oerland and

into stream channels as the

soil water becomes saturated.

!a" J !b" lead to peak discharge.

3ag Time - the time it takes from peak rainfall topeak discharge.


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The shape of the rising li#b depends on

The length of the rainstorm - a long period of rainfall

causes rise in the water table and increased oerland

flow. The intensity of rainfall -

If heay - considerable %uick flow if the soil is

incapable of soaking it in and storing it a steep rising

limb.

If light - less steep rise and flatter shape since rain is

easier to store.

The condition of the soil - If the soil is already

saturated more water flows oerland into streams andthis leads to a higher and earlier peak.

'hape of the drainage basin 5 a long narrow basin with

tributaries


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'!a#ple – e!plaining the shape of the two graphs

'!a# uestions

#ne type of %uestion that can arise about hydrographs is a comparisonbetween different hydrographs.

8hen answering these types of %uestions you must not only

describe the features of the hydrographs, but e0plain why the

hydrographs hae certain shapes. It is likely that you will be gien

a diagram or information to help and you should think about what

effects on the hydrograph the following hae*

'ie of the drainage basin

'teepness of the slopes

A B'teep slopes

Fo Trees

Impermeable rocks

Urbanised

Intense thunderstorm

:entle slopes

Aorested

6ermeable rocks

Aields

3ight steady rain

raph A raph B


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&ock or soil type !6ermeable or ImpermeableE"

'tream density

4egetation

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Hydrosphere - course notes.doc