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Rivers: Profiles &
Landforms
Higher Geography
The Hydrosphere
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River ProfileSource
of river
UpperCourse
MiddleCourse
LowerCourse
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River speed
Fastest??
Moderate??
Slow??
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Upper Course
Lower Course
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Contrasting river landformsfrom source to mouth
Channel features
Valley features
Long profile
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Upper Course - Channel features
River channel is rocky. Covered with various shapes and sizes
of boulder.
Discharge is low.
Under flood conditions rivers energy is
expended on vertical erosion with
hydraulic action and corrosion processesat work.
Potholes may form.
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Vertical erosion
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Pothole formation
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Upper Course - Valley features
Valley sides are steep and form a V shaped
cross section.
Interlocking spurs.
V shaped valley
Steep sidesZig-zag bends(interlocking
spurs)
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V shaped valley
Form due to a combination ofthe following processes:
Vertical erosion by the river
itself.
Physical weathering (eg:frost action) which provides
debris to move down slope.
Mass movement (inc: soilcreep & landslides) to movedebris down slope.
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Interlocking
spurs
River flows aroundinterlocking spurs
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Upper CourseLong Profile
Generally the gradient is steep and the
profile is uneven, particularly where
waterfalls and rapids form.
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Waterfall formation
Hard Rock
LavaSoft Rock Sandstone or Conglomerates
Soft rock is easy toerode, but the hard rockis resistant.
So over time a ledgedevelops.
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Waterfall formation
The water rushes over theledge and erodes a plunge
pool by abrasion andhydraulic action.
Hard Rock
LavaSoft Rock Sandstone or Conglomerates
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Waterfall formation
The ledge collapses intothe plunge pool, wherethe debris helps tospeed up the erosion.
Hard Rock
LavaSoft Rock Sandstone or Conglomerates
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Waterfall formation
The process is repeatedand the waterfall
gradually retreatsupstream, carving out agorge.
Hard Rock
LavaSoft Rock Sandstone or Conglomerates
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WATERFALL
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PLUNGE
POOLUNDERCUTTINGOF SOFT ROCK
OVERHANG
WATERFALLRETREATS . .UPSTREAM . .
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Formation of rapids
Resistant rock Less Resistant Rock
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Features in the Upper Course
(closer to the source)
1. Steep V-shapedvalleys
As a river cuts down
vertically into its bed,the valley side walls
become degraded by
weathering and mass
movement, so thatthe valley itself adopts
a V-shaped profile.
2. Inter-lockingspurs
Water will find the
course of leastresistance, it
therefore moves
around hard rock. The
hard rock sticks outas spurs which inter
lock.
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Upper course
3. Potholes
A circular depressionon a river bed carved
out of solid rock Pebbles caught ineddy currents andwhisked around within
a small natural crackor hollow
Commonly found
under waterfalls or
rapids where
hydraulic action is asignificant process.
Abrasion is also at
work here.
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Upper course
4. Waterfalls
A sudden step in a rivers
long profile.
The result of a toughermore resistant band of
rock cutting across the
valley.
Waterfalls can migrate
backwards to produce a
steep sided valley or
gorge.
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Waterfalls
See diagrams
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Niagara Falls
At Niagara a hard
band of limestone
overlies softer shales
and sandstones. The Niagara River
plunges 50 m causing
the falls to retreat by
1m a year and socreating the Niagara
Gorge.
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Upper course 5. RAPIDS
Cedar Rapids, USA
Rapids can also be known ascataracts.
They develop where thegradient of the river bed
increases without a suddenbreak like a waterfall.
Or where the river flow over aseries of gently dipping bandsof harder rock.
Rapids increase the turbulenceof a river and hence its erosivepower.
See diagram
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RAPIDS
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Middle Course - Channel features
Channel is now wider and has smoother
banks and bed compared to the upper
course.
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Middle Course - Valley features
River erosional energy is now increasingly
expended horizontally rather than vertically.
Lateral erosion by the rivers meanders
broadens the valley floor into a narrow flood
plain.
Meanders gradually shift their course
downstream.
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Middle Course 1
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Middle Course 2
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MeandersA meander starts as a slight bend:
Water flows faster on the outer curve ofthe bend (more energy), and slowest on theinner curve (less energy).
So the outer bank gets eroded whilematerial is deposited at the inner bank.
Over time the outer bank gets worn away(river cliff) and the inner one builds up(river beach). The bend grows into ameander.
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Meanders(refer to previous notes and diagrams)
Alternating series of irregularities develop
Poolsdeeperstretches ofslow moving water
Rifflesshallowersection offasterflow,
flowing above coarser material River develops a winding or sinuous course
Fasterflow on outer bend results in erosion
and formation of River Cliff
Slowerflow on inside of bend results in
deposition and formation of Slip-off Slope
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Meanders
Meanders develop and
migrate laterally and
downstream
Helicoidal flow further
assists meander
formation and transports
sediment from river cliff to
the slip-off slope on the
inside of the next bend.
MEANDERS
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MEANDERS
Flood plain
MeandersMost erosionon the outsideof the bend .. Fastest flow
Possible breakthrough point
Possibleox-bowlake
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Meanders
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Middle Course - Profile
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Middle Course - Profile
Gradient is now less steep.
Overall the profile is smooth but anoutcrop of resistant rock could still cause a
waterfall.
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Middle Course 1.MEANDERS
In the middle course of
the river the discharge
has increased as more
tributaries feed into the
river. Gradient has decreased
so instead of vertical
erosion, lateral erosion
takes over. See overhead for 3 types of flow
in the river channel
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Meanders
Rivers follow the path
of least resistance so
it is often forced to
follow a windingroute.
Fastest flow is on the
outside of the bend
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What causes meandering?
A) An obstruction inthe channel
- This causes thewater to be thrownto the outside of thechannel as the waterfinds the path ofleast resistance
- See diagram on overhead
B) Helicoidal flowSurface water flows towardsthe outer (concave) banks
the water descendseroding & undercutting the
bankThe bottom flow is towards
the inner (convex) bank
- eroded material is carriedalong the bed & deposited
on the slip of slope area
See diagram on overhead
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Fluvial LandformsMiddle course of
river
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What causes meanders?
C) In straight
channels there is a
regular pattern of
shallow areas (calledriffles) and deep
areas (called pools).
Spacing is usually 5
to 6 times bed width
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Fluvial LandformsMiddle course of
river
There is less friction in pools.
Thus, river flows faster and has more erosive
power.
Increased friction in the riffles slows water
down and more deposition takes place.
Continuous erosion in the pools and deposition
in the river accentuates the slight bends of a
river. See diagram on overhead
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Fluvial LandformsMiddle course of
river
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Fluvial LandformsMiddle course of
river
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Middle Course
Meanders will migrateacross the plain anddownstream
See diagram on overhead
2. Ox-bow Lakes
Handout provided
- also known as a cutoffor a mortlake
- it is a crescent shapedlake originating in ameander
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Lower Course - Channel features
The channel is now at its broadest and deepest.
Bedload is carried entirely in suspension and is
solution.
Deposition now dominates particularly duringfloods.
Erosion also occurs in the formation ofmeanders
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Lower CourseValley features
Thanks to lateral erosion the valley sides
may now be several kilometres away.
Typically it may also contain the following
features:
Floodplain & natural leves
Braided channels
Meanders
Oxbow lakes
Estuaries and deltas
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Lower Course
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Natural leves
As the river floods, sediment is dropped over allthe flooded areas but most falls along the riverchannel itself.
This sediment raises the height of the banks isflooding occurs regularly
Levees themselves do not prevent floodingbecause as the banks are raised, moresediment is dropped on the river bed, raising thewater level.
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Gentle valley sides
Flat floodplain
Layers of siltDeposited during floods
Coarse materialForms naturallevees
River is actually flowing above
The floodplain !!
Levees is oftenartificiallystrengthened
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Braided channels
Formed by the choking of the main
channel by the deposition of a
considerable amounts of the river load.
The channel splits into several smaller
channels which flow around fresh islandsof deposited material before rejoining.
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Braided channels
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Braided channels
O
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Ox-bow lakesDownstream migration of meanders produce pronounced meander loops which
may form ox-bow lakes during flood conditions
1 Lateral erosion on outside of bends of pronounced meander
2 Narrow neck of meander gradually becomes narrower
3 Neck is cut through by river during floods and river forms new straighter
channel
4 Cut-off is sealed by deposition
5 Ox-bow lake begins to silt up(Core Higher, P 65, Fig 3.36)
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Oxbow lakes
An Oxbow lake starts as a meander.During a flood the river cuts across themeander, forming a new channel.
Sediment is deposited along the sides ofthe new channel. The loops gets sealedoff and an oxbow lake forms.
The water in it becomes stagnant. Thelake will remain sealed of until either theriver floods into it or it dries out.
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Oxbow lakes
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NARROW MEANDER NECK
FUTUREOX-BOW LAKE
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Estuaries and deltas
An estuary is where a river meets the sea
(it is tidal).
Deltas are essentially the seaward
extension of the floodplain and form where
tides are too weak to remove depositsediment.
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Lower Course
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Lower course -1. Floodplains
AGGRADATION occurs as the river
bed is silted up due to deposition.
There is still some lateral erosion to
wear away the banks and widen the
valley floor, but this is weak.
A FLOODPLAIN is a mostly flat
area of land bordering a river that
is subject to periodic flooding.
It is made up of silts and sands
which have been deposited over
many years by the river
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Floodplain Formation
Formed in 2 ways:1. When river in flood
- Wetted perimeter increases,so more friction
- Deposition of suspendedload
- Alluvium deposited, andfloodplain builds up in heightover time
- E.g. it has proved impossibleto drill down to bedrock inlower Nile valley due to depth
of alluvium- Alluvium provides a very
fertile soil
2. By migration of meanders
- Deposition occurs on insidebend of meander
- Point bar deposits build up toform a slip off slope
- Ultimately the whole valleyfloor is affected as meanderswander across it
The floodplain can be widenedby lateral erosion of themeanders.
The edge of the f.plain is oftenmarked by a prominent slopeknown as the BLUFF LINE.
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Lower Course Features
2. LeveesHandout provided
Natural levees producedduring floods
Artificial levees built toprotect from flooding e.g.levees on Mississippistretch for 3,500 mileswith average height of 7mand reaching 15m inplaces.
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Lower course features
3. Terraces- These form when sea level
drops
- This could be due to tectonicuplift of plates e.g. Turkey
- Or isostatic uplift due todeglaciation (ice melts so lessweight and land rises e.g. inBritain)
- Due to the drop in sea level theriver has much more erosivepower in its lower reaches
- So the river cuts down into itsbed and the old floodplain maybe left perched above thechannel to form a TERRACE
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4. BraidingBRAIDING is the subdivision of a
river due to the build up of
deposited material in the channel.
Why does this happen?
A) Easily eroded river banks e.g. if
made of loose sands and gravels.Braiding occurs in rivers which for
short periods of the year carry a
very heavy load in relation to their
velocity e.g.
B) A glacial out-water stream ladenwith sediment eroded by glacier.
C) A stream during snowmelt in
Alpine or Arctic areas.
D) Rapid and frequent variation in
stream discharge
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Braiding continued
Why does the river divide?- When discharge falls
competence and capacity arereduced.
- The channel becomes chokedwith material which it cannot carry.
- Load is deposited.- Dumped material forms islands in
the channel called EYOTS (orBRAID BARS).
- River is forced to divide aroundEYOTS.
- The location and number of
channels and islands is notpermanent, these move aboutmaking navigation difficult.
- The smaller subdivided channelsare faster and can cut into thebed, steepening the gradient andincreasing efficiency.
Generally braided channels occur
in summer when discharge is low.In winter greater discharge
enables material to be transported
again and the river can fill the
whole width of its channel again.
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Lower course 5. Deltas
A DELTA is the flat alluvial area atthe mouth of some rivers where
the mainstream splits up into
several DITRIBUTARIES.
Flooding from distributaries builds
up the delta. The largest deltasin the world are the Ganges, Nile
and Mississippi.
Conditions for formation:
A) Huge amount of sediment in the
river
B) River gradient is low
C) Little current or tidal action as
this would sweep sediment away
Most of the worlds deltas are
decaying because people builddams which hold back sediment.
Tides are also changing and getting
higher, so eroding deltas.
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Mississippi Delta
BIRDS FOOT DELTA
River has many distributaries
which extend out to sea like
the claws of a birds foot
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Nile Delta
ARCUATE DELTA has a
rounded, convex outer
margin.
When Mississippi and Nile
reach the sea, the meeting
of fresh and salt water
produce an electric charge
which causes clay
particles to coagulate andto settle on the seabed,
this process is called
FLOCCULATION.
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Tiber Delta
CUSPATE DELTA
Material brought down by
the river is spread out
evenly on either side of
its channel.Deltas are:
- Fertile
- High flood risk areas
- Difficult to navigate as
shallow and change
shape
Ri
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River
Running water is the most important agent oferosion on the continents and the streamvalleys are the most common landforms.
Rivers flowing to the oceans drain about 68 %of the Earth's land surface. The remainder ofthe land either is covered by ice or drains toclosed basins.
River gradually mould the land by erodingaway the material in some place anddepositing it in other
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A river system consists of a main channel (trunk stream) and all of the
tributaries that flow into it or joining the trunk stream.
A RIVER SYSTEM CAN BE DIVIDED INTO THREE SUBSYSTEMS:
collecting system (branches) -- consisting of a network of tributariesin the headwater region, collects and funnels water and sediment to
the main stream transporting system (trunk) -- the main trunk stream, which functions
as a channelway through which water and sediment move from the
collecting area toward the ocean. (Erosion and deposition also occur
in a river's transporting system)
dispersing system (roots) -- consists of a network of distributaries atthe mouth of a river (delta), where sediment and water are dispersed
into an ocean, a lake, or a dry basin
Partsof River
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tributary : a stream flowing into or joining a larger
stream distributary : numerous stream branches into which a
river divides where it reaches its delta
upstream : moves toward headwater (up the regional
slope of erosion) downstream : moves toward mouth of river (delta)
Delta : a large, roughly triangular body of sediment
deposited at the mouth of a river
Meander : a broad, looping bend in a river
Braided : river is divided into multiple channels by
alluvial islands. Braided rivers tend to have steeper
gradients
Partsof River
Drainage Pattern
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Irregular branching pattern (tree
like) in many direction.
It is common in massive rocks and
in flat lying strata
Due to strong resistance of rocks
headward development of valley is
negligible.
Drainage Pattern
Dendritic
Parallel Parallel or sub-parallel drainage
formed on sloping surface.
Common in terrain with
homogeneous rocks. Development of parallel rills, gullies
or narrow channels are commonlyseen on steeper and gently slopingsurface
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Streams radiates out from the center of the
topograhic high
common in Volcanic terrain
Channels marked by right-angle bends
Commonly due to presence of joints
and fractures in the massive rocks or
foliation in metamorphic rocks
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Consequent Stream:
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Consequent Stream:
A stream following the slope.
Development of slope may
be due to sudden tectonic
uplift
Subsequent Stream:
A stream that develops later on, carving the
softer rocks and flow at almost right angle to
the original slope of the land
FLUVIAL LANDFORMS
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Alluvial Fan
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Alluvial fans are fan-shaped deposits ofwater-transportedmaterial (alluvium).
They typically form atthe base oftopographic features
where there is amarked break in slope.
Consequently, alluvialfans tend to be coarse-grained, especially attheir mouths. At their
edges, however, theycan be relatively fine-grained.
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Braided Channel
Levee
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s
Oxbow
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lakes
Riversystem
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system
Headwat
er
TributariesTrunk
stream
Distributaries
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