1. Stream Dynamics. Weathering. Erosion. Processes which impact the course of a river over time. Deposition. Stream discharge. Gradient (slope). Tectonics. 2. Factors which influence water velocity. Stream Discharge. The volume of water in a stream.
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Processes which impact the course of a river over time.
Factors which influence water velocity
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 ___________
During what time of the year will the greatest stream erosion occur in New York ?
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 channel
A rocky stream bed
Rapids and waterfalls
Downcutting is dominant in this stream in Ithaca , NY.
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.
The path the stream follows.
The bends in the river channel.
The outside of a meander where erosion occurs.
The inside of the bend where deposition takes place.
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
Inside: slower flow
Depositionat the inside of the channel
Outside: Faster flow
This process forms meanders.
Stream Bed Profiles
When the channel is straight, the stream bed becomes symmetrical.
Fastest flow is always:
Above the deepest part
Just below the surface
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 )
Particle size decreases
Horizontal sorting results from the gradual slowing of the river.
The Delta grows as sediments are deposited.
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.
Decrease in particle size.
The Catskill delta
Water fall Recession
The position of a waterfall gradually migrates upstream.
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.