Stream Dynamics
Processes which impact the course of a river over time.
WeatheringErosionDeposition
Stream discharge
Gradient (slope)
Tectonics
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Factors which influence water velocity
Stream Discharge
The volume of water in a stream.As discharge increases, velocity increases.
As velocity increases, kinetic energy ______________
As kinetic energy increases, the size and amount of weathered material the stream can transport _____________
As water velocity increases, erosion ___________
increases
increases
increases
During what time of the year will the greatest stream erosion occur in New York ? Spring Why ?
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Downcutting and Lateral Erosion:
When water velocity is high and the force of erosion is directed downwards, downcutting deepens the stream channel.
When downcutting is dominant, streams will have:
A straight channelA rocky stream bed
Rapids and waterfalls
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Downcutting is dominant in this stream in Ithaca , NY.
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With gradual slopes and softer bedrock or sediment, lateral erosion dominates.
With erosion directed toward the banks of the stream, the channel begins to change.
Over time, the bends become more eccentric.Eventually, the bends may get cut off forming Ox-Bow Lakes.
Ox-Bow Lakes
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Stream FeaturesChannel: The path the stream follows.
Meanders : The bends in the river channel.
Cut bank: The outside of a meander where erosion occurs.
Point Bar: The inside of the bend where deposition takes place.
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Water always seeks the path of least resistance as it flows toward the lowest points. A straight channel is most likely
found where slopes are steep and the stream bed is resistant rock.
With changes in slope and bedrock resistance, the channel begins to change.
Erosion at the outside of the channel
Deposition at the inside of the channel
Outside: Faster flow
Inside: slower flow
This process forms meanders.
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Stream Bed Profiles
Cut bankPoint bar
Cut bankPoint Bar
A B
X Y
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When the channel is straight, the stream bed becomes symmetrical.
ST
Fastest flow is always:
Above the deepest part
Just below the surface
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Deposition at the mouth of a river.Formation of a Delta.
As the river enters a body of water, velocity decreases.
Due to the loss of Kinetic energy, transported material is deposited. ( Drops out )
Horizontal sorting results from the gradual slowing of the river.
Particle size decreases
The Delta grows as sediments are deposited.
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Conglomerate
Sandstone
Siltstone
Shalefine
coarse
This sequence of sedimentary rocks indicates a delta deposit. Deltaic deposition
The Catskill region of New York State shows this type of sequence in the sedimentary structure.
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The Catskill delta
Decrease in particle size.
?
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Water fall Recession
The position of a waterfall gradually migrates upstream.
Limestonesandstone
Less resistant shale or siltstone
The water plunging over the falls removes the softer less resistant underlying bedrock.With the supporting rock removed, the overlying more resistant rock cracks off and falls.
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