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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