Stream dynamics
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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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Stream Dynamics

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Stream dynamics

1

Stream Dynamics

Weathering

Erosion

Processes which impact the course of a river over time.

Deposition

Stream discharge

Gradient (slope)

Tectonics


Stream dynamics

2

Factors which influence water velocity

Stream Discharge

The volume of water in a stream.

As discharge increases, velocity increases.

As velocity increases, kinetic energy ______________

increases

As kinetic energy increases, the size and amount of weathered material the stream can transport _____________

increases

As water velocity increases, erosion ___________

increases

During what time of the year will the greatest stream erosion occur in New York ?

Spring

Why ?


Stream dynamics

3

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


Stream dynamics

4

Downcutting is dominant in this stream in Ithaca , NY.


Stream dynamics

5

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.

Ox-Bow Lakes

Over time, the bends become more eccentric.

Eventually, the bends may get cut off forming Ox-Bow Lakes.


Stream dynamics

6

Stream Features

Channel:

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.


Stream dynamics

7

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 dynamics

8

Stream Bed Profiles

X

Y

Point Bar

Cut bank

A

B

Cut bank

Point bar


Stream dynamics

When the channel is straight, the stream bed becomes symmetrical.

9

Fastest flow is always:

Above the deepest part

Just below the surface

S

T


Stream dynamics

10

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.


Stream dynamics

11

This sequence of sedimentary rocks indicates a delta deposit. Deltaic deposition

coarse

Conglomerate

Sandstone

Siltstone

Shale

The Catskill region of New York State shows this type of sequence in the sedimentary structure.

fine


Stream dynamics

12

?

Decrease in particle size.

The Catskill delta


Stream dynamics

13

Water fall Recession

The position of a waterfall gradually migrates upstream.

Limestone

sandstone

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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