River Profiles

River Profiles and
Fluvial Landforms
River Capture /
Stream Piracy

Learningobjectives
Processes of River Transportation
River Profiles : Long Profile
River Profiles : Cross Profile
Fluvial Landforms
River Abstraction / Stream Piracy.

Processes of river transportation Schuters:
Pg.165

Longitudinal Profile: River from Source to Mouth

V-shaped valley
Vertical erosion (Turbulent flow)
Waterfalls
Rapids
Gorges
Pot-holes
Interlocking spurs
Asymmetrical channel
Meanders
Transportation
Floodplains
Slip-off slopes
Truncated spurs
Large channel
Deposition
Braiding
Ox-bow lakes
Large flood plains
Levees
Deltas
River Channels Pg.127
Click for video
Longitudinal Profile is the profile
of a river from it’s Source to it’s Mouth.
Youthful stage
Mature stage
Old age stage

Stages of Stream Development
Initial Stage:
Fast moving
stream, narrow
valley
Mature Stage:
Meanders develop,
widening floodplain
Old Age Stage:
Wide floodplain,
yazoo streams,
and oxbow lakes
develop

Back
Upper Course where alternate layers of hard and soft rock is found!

CC- Geoff Edwards
Back
Erosion

CC- Aerial Photography
Back
Middle

CC- Martin Third
Back
Flood plain

CC- ecstaticist
Back
Lower Course

Ronnie Raindrop’s journey… Instructions
Copy the following 14 slides (slides 17-29) into a new
PowerPoint presentation and complete the
following :
1. Rearrange the slides so that they show the correct
order as you travel down a river. Remember that a
river has an Upper, Middle and Lower stage. By
the way the numbers don’t go in order!
2. On each slide write what Ronnie can see (fluvial
erosional and depositional landforms and the
process at work) on his journey. You could use text
boxes or speech bubbles to do this.
3. Add your name and form to the title slide.
4. Delete this instruction slide.
5. Print out your work and staple it.
6. Finally, hand it to your teacher.
Well done, mission complete…

1
Source / Origin of River
Youthful stage
Watershed
Catchment area
Orographic uplift
Formation of clouds

7
Youthful stage
V-Shaped Valley
Vertical erosion
Turbulent flow

5
Waterfall
Youthful stage
Turbulent flow
Alternate layers of hard and soft rock

2
Rapids
Youthful stage
Turbulent flow
Large bed load

6
Interlocking spurs
Youthful stage
Turbulent flow
Large bed load

11
Temporary Base Level of erosion

3
Mature stage
Meandering river
Large channel

10
Old Age stage
Meandering river

Old Age stage
Meandering river
River flood plain
8

4
Old age stage
Meandering river
Ox-bow lake

9
Old Age stage
Braided river
Velocity of river is reduced
Deposition occurs

12
Ultimate Base Level of erosion
Lowest level to which a river can erode
Mouth of the river

Profiles
Cross
Profile
Longitudinal Profile
Cross Profile
Is the profile of a
river from Bank
to Bank
Longitudinal Profile
is the profile of a river
from it’s Source to it’s
Mouth.

Ungraded vs. Graded Streams
Graded stream: Balance between transport capacity and sediment load.
Maintained by altering the shape of the channel and stream profile.
Rate of erosion = Rate of Deposition
Smooth concave profile
Ungraded profile / stream: Rate of erosion is not equal to rate of deposition
Rough concave profile

Long Profile
1) Name the typical shape that the river strives to achieve.
Smooth concave profile. [Graded profile] Dotted line on profile
2) What is the real shape it accepts?
An uneven, concave profile, steep at the source and gentle at the mouth.
3) Name (a) a temporary (local) and (b) a permanent (ultimate) base level of erosion.
(a) Dam (b) sea (the lowest level to which a river can erode)
4) Name three ways in which the above river may be rejuvenated.
Dam wall bursting. Rising of the land. Sinking of the sea.
5) Name 3 factors that disrupted the above longitudinal profile.
Rapids, waterfall and dam
6) Where does erosion occur fastest? Give a reason for your answer.
In the middle section, stream volume and load have increased. Erosion is thus faster.

Cross Profile
1) What type of river channel will produce a
symmetrical cross profile?
Straight stream
2) Which 2 factors determine the different cross profiles that a river may display?
Climate and Geological conditions
3) Which 2 erosive processes are responsible for eroding the valley sides.
Mass wasting and undercutting
4) Account for the shape of the cross profile on a bend.
Outer bend (undercut slope) is characterized by erosion since the water flows faster.
Inner bend (slip-off slope) is characterized by deposition, since the water flows slowly.

Cross Profile
Schuters:
Pg.167*
Notes Oxford:
Pg.122

• Velocity varies within the channel
– Highest velocity is in
the center of the channel
– Drag slows water along
the bottom, banks, and
top (water-air interface)

Channel shape and velocity
Schuters:
Pg.167

Activity 6: Channel shape and velocity Pg.122

1) Meanders / Ox-bow Lake
Fluvial Landforms
 River reaches flat land
 Begins to meander
 Velocity is highest on the outer bend
- erosion – undercut bank – river cliff
Velocity is lower on the inside bend -
deposition – slip-off slope – gradual
slope.

Channel shape is based on the velocity of the stream and resistance of rock it
is cutting into.
Water in streams tends to move quicker in the center of the stream and
slower towards the outside.
Outside of meander is called a Undercut slope and is associated with erosion.Inside of meander is called a Slip-off slope and is associated with
deposition.

Fluvial Landforms : Incised / Intrenched Meander

Fluvial Landforms
2) Waterfalls
 Forms when resistant layer of rock
prevents vertical erosion
 Softer underlying layers are eroded
 Resistant layer is undermined and
collapses.
Waterfall retreats upstream.
Forms a Gorge or Ravine.

Copyright © Houghton Mifflin
Company. All rights reserved.
Geology, 14b–52
Fluvial Landforms
Formation of a Waterfall

Fluvial Landforms
3) Levees
 Form on the floodplain on the lower course
 Flooding causes overflowing of banks
 Heavier deposits occur repeatedly on the banks
Deposits are built up to raised banks known as levees
May be artificially raised and strengthened as flood protection
Swamps may form on the floodplain

Deposition and Erosion of River Bars
Flood: Increased
discharge and
erosion!
Normal Flow
Post-flood; new
bars deposited

The Aswan Dam and the Nile DeltaFluvial Landforms
4) Deltas
 A large and constant supply of silt.
 A slow flowing river with water
all year
 No strong tidal effect in the sea
A calm, shallow sea with:
No rapid subsidence of the sea floor
No strong currents in the sea
When a river enters the sea or a lake
the gradient is gentle and the flow
speed of the river is reduced resulting
in the deposition of sediments
causing the river channel to become
blocked.
Requirements for a Delta to form

The Irrawaddy River Delta
This river delta
in Burma is
one of the
world’s great
rice producing
regions
Fertile mud
and sand
have been
deposited
here during
the last 2
million years
mangrove
forest
Sediment
plumes

Fluvial Landforms after rejuvenation

Rejuvenation is when the river flows faster due to the following:
 Global drop in sea level
Uplift of land
 Increase in rainfall
River Capture
Rejuvenation results in:
 Incised rivers (rivers cut into the plain)
River Terraces
Knickpoints

How Terraces Form
Incised River

Stream Terraces - Jackson Hole, WY

Fluvial Landforms : After Rejuvenation
Name the landforms that may develop after a river has been rejuvenated.
Intrenched Meander
 These are formed when rejuvenation
occurs in a stream which is already
meandering
 The stream now meanders in a deep,
steep-sided gorge eg. Fish River
Canyon and lower course of the
Breede River
Valleys within Valleys
 When streams are rejuvenated
fairly rapidly and the base level
drops substantially, a valley can
be formed within a valley.
Terraces
• When rejuvenation of a river flowing on a wide
valley floor (flood plain) occurs, a new valley is
carved into the old one and parts of the earlier
valley remain as terraces. E.g. Canyons
• Terraces may be:
Matched
Unmatched
• Such terraces can be seen along the
banks of the Vaal river in the vicinity of
Bloemhof, Christiana and Delport.

A Question of Rivers
1 2 3
4 5 6
7 8 9

1
a) Which stage of the river will this type of erosion take place in?
b) Which type of erosion is responsible for the formation of these
circular depressions?

a)The circular depressions are little pot holes
and they develop in the Youthful stage of the
river.
Small stones are swirled around in them when
the river is flowing higher and faster than it is
at present.
b) The pot holes are eroded by the abrasive
action of the swirling stones.
1

2
What is required for incision of the river to occur?
Drag and drop the following labels in the correct position:
Fall in sea level Waterfall retreats cutting a lower valley New flood plain forms
River bluffs

2Rejuvenation is required for incision of the river to occur.

3
Identify the physical features by dragging and dropping the
following labels in the correct position:
meanders broad, flat flood
plain
ox bow lake limit of tidal
influence
embankments/levees

ox bow lake
limit of tidal
influence
meanders
broad, flat flood plain
embankments/levees
3

4
What river feature occupies the centre of this photo?
How does the river change downstream of the feature?

This feature is a confluence. It occurs where a
tributary joins the main stream or river.
Downstream of a confluence , the river increases
in width. The discharge of a river (the volume of
water it is carrying) also increases significantly.
4

5 What features
identify this
stretch of
river as part of
its upper
course?
interlocking spurs
steep valley sides
steep long profile
absence of flood plain
large bed load
Drag and drop the
following labels in
the correct position.

interlocking spurs
steep valley sides
absence of flood plain
steep long profile
large bed load
5

6
Why has a waterfall developed here?
Label the following:
a band of hard
rock interrupts
the river’s
course
An overhang develops
where the softer rock
below is eroded. In
time this will collapse.
relatively
softer rock
plunge pool

a band of hard
rock interrupts
the river’s
course
An overhang develops
where the softer rock
below is eroded. In
time this will collapse.
relatively
softer rock
plunge pool
6

7
How would you know that this valley was not
carved by the river which flows in it today?

This valley is a U-shaped valley in the Scottish Highlands.
It was eroded by ice during the Ice Age.
It is much too large and deep to have been carved by the
small river which now flows in it.
The river is called a ‘misfit’ as it is not in keeping with
the scale of its valley.
Although the river is in a highland valley, it displays
features of a valley in its lower course (meanders). This
is because the valley floor is so flat.
7

8
Identify the physical features by dragging and dropping the
following labels in the correct position:
small tributary no flood plain steep valley sides
Perennial Straight
stream
steep long profile of a tributary

steep valley sides
small tributary
no flood plain
steep long profile of a tributary
8
Perennial Straight stream

9
Describe and explain the differences between
the sides (banks ) of the river

9
On the inside of the meander
water is flowing more slowly.
This results in deposition and
the formation of the slip-off
slope or river beach.
On the outside of the meander
water is flowing more quickly.
This results in erosion and the
formation of a undercut slope
or river cliff.

Abstraction of a Drainage Basin
 A watershed remains in
the same position only if
the rates of erosion on
either side are equal
 The river (B) flowing down
the steeper gradient
erodes faster and moves
the watershed back from
position 1 to 2
 Water falling on the area
between 1 and 2 will thus
no longer flow down gradient
B, as it had previously done,
but will be captured to fall
into the catchment area
belonging to A
Factors favouring river abstraction

Factors favouring river abstraction
Schuters pg 176

Activity 14: Abstraction of the eastern escarpment Pg.136

Activity 15: Identifying river capture Pg.137

River Profiles

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