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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
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%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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