1. River Erosion & its
Associated Features
Presented By:
Vasu Goel
P.I.E.T.
2. Longitudinal River Profile
Elevation(feet)
0
3,000
Headwaters
Ultimate
Base level
River Length (Miles)
100 0
This diagram outlines the longitudinal profile of a
river basin from the headwaters to the ultimate
base level, or sea level. A rivers gradient is
steepest near the headwaters and gentlest near
the base level. In South Carolina, the steepest
sections are often found in the blue Ridge and
Piedmont, while the gentler gradient occurs in the
Coastal Plain. River length, or distance, is
measured from the rivers mouth to its
headwaters, seemingly reversed from what one
might expect.
Longitudinal Profile and Watersheds
Headwaters:
multiple low-order
streams near
drainage divide
Base level:
single outflow and
highest order stream
This figure is a hypothetical river basin. The black dotted line
represents the drainage divide and the numbers refer to stream
order. Any rainfall that falls within the black dotted line will
eventually flow into the main strem river and out at the mouth.
Stream order increases from the headwaters to the base level.
In this example, the river is a5th-order river.
Stream Order:
1st order and 1st order = 2nd order
2nd order and 2nd order = 3rd order
3rd order and 3rd order = 4th order
4th order and 4th order = 5th order
And so on, 5 and 5 =6, 6 and 6 =7th order…
5
1
1
1
2 2
1
1
3
4
3
4
5
13. A river can erode material from its bed and
banks in 4 main ways
Chemical Action
Abrasion
Hydraulic Action
Attrition
14. The Work of Rivers
The erosional work of streams/rivers and shapes
the landscape through which they flow.
functions of rivers
a. Erosion
b. Transportation
c. Deposition
15. The Work of Rivers
Erosion
•A river may erode in 4 ways
1.Abrasion/corrasion
Load carried by a river will grind against its
bed and sides.
This process slowly wears the bed and sides
away.
16. The Work of Rivers
2. Attrition
When thrown against the sides and bed of
rivers, the load gets broken into smaller
pieces.
17. The Work of Rivers
3. Hydraulic action
The work of turbulence in the water.
Running water causes friction in the joints of
rocks in a stream channel
Joints may be enlarged
18. The Work of Rivers
4. Solution/Corrosion
Certain minerals in rocks like limestone can
be dissolved in water.
Rocks are then eroded.
19. Methods of Transportation
Rivers transport material in 3 main ways
Solution - Some minerals (particularly in limestone areas) dissolve easily in
water and are not visible to the naked eye
Suspension- As the speed or velocity of a river increases, it is able to pick up
and carry larger and larger particles in its flow. Where particles are carried
along in the flow and are not in contact with the river bed, they are said to be
travelling in suspension.
Bed load- heavy bigger rock fragments moves along with the flow of water is
known as bed load.
20. Methods of Transportation
Siltation - Heavier particles may not be held in the flow all the
time but may be bounced along the bed
Traction - The heaviest particles are rolled along the bed. Such
particles may only be moved when the river has a large volume of
water in it
21. 21
Boulders are large and semi-rounded, due to
attrition within the load and abrasion with
the stream bed and banks
Why are they rounded?
River load in upper course
23. • A kettle-like small depressions in the rocky beds of the river valleys are
called pot holes which are usually cylindrical in shape.
• Pot holes are generally formed in coarse-grained rocks e.g. sandstone and
granites.
• The diameter of pot holes ranges from a few centimeters to several
meters.
• They are found in the upper course of a river where it has enough
potential energy to erode vertically.
• The pot holes go on increasing in both diameter and depth.
Pot Hole
25. Waterfalls
• Waterfalls occur where there is resistant bedrock, abrupt changes in bedrock resistance, or
along fractures or faults in the bedrock.
• Less resistant materials are weathered more quickly than resistant rocks, creating stair-
stepped ledges or drop offs where waterfalls occur. Less resistant rocks may also form pools
between resistant rocks that form waterfalls.
• Faults and fractures often provide natural pathways for the downslope movement of water.
• The location of the waterfalls origin may be referred to as a “knick-point”, continued
weathering by the stream flow causes the knick-point to slowly migrate upstream.
• Most waterfalls in South Carolina occur along streams in the Blue Ridge, Piedmont, and the
along the Regional Fall Line where there are rock layers of varying resistance.
This waterfall was formed by differential weathering
between the softer shale and harder more resistant
limestone.
Photo: SCGS
Lower White Water
Falls in the Jocassee
Gorges area of South
Carolina drops nearly
200 ft. Here, the
Toxaway Gneiss forms
a resistant bedrock that
the Lower White Water
River flows over before
draining into Lake
Jocasse.
38. 38
Lower Severn Valley
Well developed
meanders with bars
in the channel
indicating high
sediment load
Very gentle valley side
gradients
Very wide
floodplain
44. A flood occurs whenever a river overflows its banks
(over ‘bank full discharge’). However, a flood
becomes a problem when the water rises to a level
where it Destructs property and life.
bank full
discharge
Meander cross
section
What is a Flood?
45. Flood plains
• Flood plains are
constructive, depositional
landforms created by
stream flow and sediment
deposition.
45
This aerial view of the Mississippi River
Valley contains many typical floodplain
features. The darker, green areas are
floodplain forest and they likely flood the
most frequently and thus are not
developed with agriculture or housing.
The surrounding patchwork represents
agricultural fields and other developed
lands that are probably at a higher
elevation formed by natural or artificial
levees.
Pointbar
Cutbank
Oxbow
Lakes
Infilled
Channel
46. • The narrow flat surface on either side of the valley floor are called river
terrace.
• Some times, the river valleys are frequented by several terraces on either
side wherein they are arranged in step-like forms.
• River terraces are generally formed due to dissection of fluvial sediments
of flood plains deposited along a valley floor.
• Terrace represents the level of former valley floors and the remnants of
former flood plain.
River Terrace
47. Floods and Flood Control
Floods
A flood occurs when the discharge of a
stream becomes so great that it exceeds
the capacity of its channel and overflows its
banks.
Measures to control flooding include
artificial levees, flood control dams, and
placing limits on floodplain development.
50. The River’s Journey
Rivers usually begin in the mountains.
They flow downhill onto flat land and into the sea
51. Characteristics of Streams
• Water always flows downhill, even on the
slightest of slopes.
• The speed of water flow depends upon the
slope. As slope increases, the velocity of the
water increases.
52. Running Water is the Predominant
Agent of Erosion on the Earth
• Every stream and its branches make up a
single system that collects all the runoff
within a definite area called the drainage
basin of the system.
• A stream consists of running water, the land
surface it drains, the sediment it transports,
and the potential energy used to drive it.
53. What determines a streams
characteristics
• Stream Discharge: the volume of water that
passes a point in the stream during a given
amount of time.
• The average velocity of a stream increases as
its discharge increases.
54. Life History of a Stream
• YOUTHFUL STREAM
• Steep gradients
• V-shaped cross sections
• Rough sediments flowing rapidly down
stream.
• Due to greater water velocity larger sediment
can be moved.
55. • Sediments cut through bedrock as they are
moved along
• Common to find rapids and waterfalls due to
differences in resistance of the bedrock to
weathering.
58. Mature Streams
• Potential energy for cutting and removing rock
becomes less.
• The average gradient is decreased.
• Velocity near the bed becomes less.
• The size of sediment that can be moved
decreases.
• Bed becomes covered with loose material, thus
protecting it from further erosion.
59. • Cutting action of the stream becomes very
slow.
• The base of the V has been widened due to
weathering and the action of tributaries the
valley now has gentle slopes.
• Meanders begin to form
• There is an increase in the volume of water
that is carried.
• A greater mass of sediment can be carried,
but most of it is silt and clay.
60.
61. Old Streams
• Gradient becomes extremely small and only
the finest of sediments can be moved.
• During times of peak flow the banks will
overflow and flood the nearby portions of its
valley.
• When the flow subsides a layer of silt and clay
is left behind on the valley surface, this is the
flood plain.
62. • Meanders are strongly looped and from time to time
they become cut off to form oxbow lakes.
63. Locations of Stages
• It is unlikely that any stream is at the same
stage of development throughout it entire
length.
• Most streams tend to have the characteristics
of youth near their source and of old age near
their mouths and to be in the mature stage
somewhere in-between.
• A stream can be rejuvenated through crustal
uplift.
64. The river cuts downward to
form a ‘V’shaped
valley. The river starts
to meander
65. River uses its meanders to cut from side
to side eating into
the valley
Floodplain
starts to
form
1
2
68. Alluvium = silt deposited by a river
Alluvial fan Caused when a stream
falling from a side valley
reaches flatter ground on
the valley floor.
Material is dropped at
the ‘break of slope’ to
form this fan shape.
(This is really a depositional feature.)
Erosion/Deposition
70. Deltas
Deltas form where the mouth of a river meets its ultimate base level at the ocean or
sea. As the river’s velocity decreases, it looses the capacity to carry its sediment load
and the resulting deposits form a delta. Delta shapes and forms vary depending on
tidal influences, waves, currents, sediment type and quantity, river discharge, and the
stream gradient near the outlet. The most common types of deltas include bird-foot,
estuarine, and arcuate.
Not all rivers form deltas, for example the Amazon deposits its sediment load directly
into the ocean onto an underwater seaward sloping continental shelf. The Columbia
River in the northwest United States, lacks a delta altogether, because the currents
are too strong and erosive for the sediments to deposit.
Mississippi River Delta: Bird-Foot Delta
A bird-foot delta contains a large channel with multiple
smaller distributary channels draining off from the main
channel and depositing sediments. They generally form
with rivers that have a high sediment load and flow
into an area with minimal tidal influences. This false-
color infrared image provides a satellite view of the
Mississippi River delta. This delta has shifted positions
several times over the last 5000 years in relation to
changes in the Mississippi River. Scientist recognize
atleast 7 distinct deltas. The most recent began
forming 500 years ago and forms a classic bird-foot
delta.
