Stream/River Erosion &
Deposition
What is a Stream/River?
• A stream is a
moving body of
water that
eventually
connects to an
ocean
A river is
simply a
LARGE
stream!!
Stream / River Characteristics
1. Velocity – how fast or slow the river is moving.
This determines the rivers ability to erode
sediments
Which river has a greater velocity?
Stream / River Characteristics
2. Gradient – the slope or steepness of the
river
The steeper the gradient, the more energy
Stream / River Characteristics
3. Discharge – the amount of water moving by
a certain point of the river in a set time
The Amazon River in South America
has greatest discharge 212,400 m3/s
Mississippi River in USA has 7th
greatest discharge at 17,300 m3/s
Stream / River Characteristics
4. Stream Channel – the course that the water
flows in a river
Following a River from
Source to Mouth
• A river begins at the
source/headwaters
– This is usually where you find
the steepest gradient
– You may also find V-shaped
valleys here
Following a River from Source to Mouth
• Alluvial Fan: A fan-shaped deposit of sediment that
forms when a stream drops downward from a higher
elevation and encounters the valley floor. The stream
slows down, depositing fine silt, sand, or other sediments
it is carrying.
Waterfall Formation
The stream bed
has soft and hard
rock.
The softer rock
erodes MORE
QUICKLY as the
river flows over it.
Eventually there
is a big enough
difference in the
rock layers to
form a waterfall.
Following a River from Source to Mouth
• As the river continues, you will also find
many tributaries – this is where one stream
empties into another
As more tributaries add
water to the main river,
the amount of discharge
increases
Tributaries
Following a River from Source to Mouth
• As the river moves downhill, it will erode its
channel until it hits base level
• Base level is the lowest point to which a
river can erode its channel.
Following a River from Source to Mouth
• As a river approaches base level, it can
develop meanders – bends in the stream
channel
Following a River from Source to Mouth
• Delta - a fan-shaped sediment deposit where
a river empties into an ocean at the mouth
Lena
River
Delta in
Siberia
New Orleans: Built on
Mississippi River Delta
Ox Bow Lakes
Meanders can turn into Oxbow
lakes…here’s how
Ox Bow Lakes
1.Neck of meander is gradually eroded
2.Once cut off, the water takes the
quickest/shortest route
3.What’s left behind is the Ox Bow lake
Sediment Transport in Rivers
• Rivers & Streams carry sediment in 3 ways:
– In solution (dissolved load)
– In suspension (suspended load)
– Scooting or rolling along bottom (bed load)
http://www.youtu
be.com/watch?v
=LhbEvV5hqCo
1. Dissolved Load
• Sediments that are dissolved in river water
2. Suspended Load
• Fine-grained sediment (like sand, silt, clay) that
remains in the water during transportation
– Usually what you see that makes a river look dirty
– Most sediment carried by a stream is suspended
– This amount increases dramatically during floods
3. Bed Load
• Heavier, coarse grained sediments that
travel along the bottom of a stream.
– Causes the most stream erosion!
– Sediment may not move frequently
Over 55% of U.S. rivers and streams are so polluted that
they are no longer safe for fish and other aquatic life!!
Quiz Vocabulary
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•
Stream
Velocity
Gradient
Discharge
Stream Channel
• Source/Headwaters
• Alluvial Fan
• Tributaries
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Base Level
Meander
Delta
Ox Bow Lake
Dissolved Load
Suspended
Load
• Bed Load