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Fluvial Systems (Rivers)

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Fluvial Systems (Rivers). Click the link for an interactive tour through the water cycle. http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/. Water that flows across land or is stored above ground is known as surface water.

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http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/

Water that flows across land or is stored above ground is known as surface water.

• Although rivers are unimportant as reservoirs for water, they are absolutely crucial to the water cycle.

They are the major route by which continental rain and the products of weathering reach the oceans.

Stream velocity-the speed at which water flows through a stream. The higher the velocity, the greater the erosive force of the stream

• Numerous factors affect the velocity of water flow in a stream:

-gradient

-channel shape

-channel size

-channel roughness

-discharge

distance water travels

V = -------------------------------------------

time required to travel that distance

Figure 16.14

The higher the velocity – the more turbulent the flow.

The more turbulent the flow – the higher the erosive capacity.

The work of running water includes:

-Transportation of sediment

-Erosion of channel (abrasion + dissolution)

-Deposition of sediment

The water

velocity

required to

pick-up and

transport

sediment

grains

depends on

their size.

Stream Load

• A stream can carry its load in three different ways:
• 1.________ – material is dissolved
• 2.__________ – particles are held up by stream’s moving water
• 3._________ – material pushed or rolled along the stream’s channel

solution

suspension

bed load

TRANSPORTATION

suspended load = mud

bed load = sand + gravel

Discharge is the amount of water that flows past a point in a certain amount of time.

Discharge is dependent upon velocity, depth, and width of the stream.

Discharge = _______ x _____ x _____

velocity

depth

width

Discharge varies from stream to stream, AND

from time to time AND place to place along

a single stream.

A stream’s discharge and velocity as well as the

sediment influx determine the morphological

features formed by a river system.

The following slides contain various river system

features.

Figure 16.14

-Meanders develop because the velocity of water

in a stream is non-uniform.

-The maximum velocity occurs on the outsides of

the meanders where erosion occurs. Deposition of

alluvium occurs on the insides.

Point bar- a depositional feature formed when the velocity on the inside of the meander slows down and sediment falls out of suspension.

• Cut bank- erosional feature formed on the outside of the meander due to the highest velocity of water removing sediment through erosion.
• The 6/10ths rule is applied to determine where the location of the fastest moving water in a river. The depth of the river is multiplied by 0.6

Point Bar

Cut bank

Braided streamsdevelop when sediment

load is too large for a

single channel to carry

so numerous channels

evolve.

Migration of meanders lead to the formation

of abandoned meanders and oxbow lakes.

Rejuvenation of a stream occurs when tectonic

processes reactivate uplift in a region and

cause streams to begin downcutting again.

terraces

entrenched meanders

A watershed is the

entire region from which a stream and its

tributaries receive their water.

Drainage

Basin

of the

Mississippi

River

Watersheds

of North

Carolina

When the amount of water in a stream exceeds the capacity

of the stream channel the water rises up over the banks

and floods the adjacent lowland called the floodplain.

A stream rises to its

bankfull stage (just

filling channel) about

once every 1.5-2 years.

The physical

characteristics of the

stream channel are

adjusted to carry this

volume of water.

http://www.coolgeography.co.uk/GCSE/AQA/Water%20on%20the%20Land/Meanders/Landforms%20Meanders.htm

Floodplains can be many tens

of miles wide and it may be

impossible to see the river from

parts of the floodplain.

Figure 16.36 A and B

Floods are a natural,

recurring phenomenon,

but the frequency and

severity of flooding can

be made worse by

human activities.

1993 Midwest

Floods

ReferencesDr. Terri Woods

http://core.ecu.edu/geology/woods/Rivers1_files/frame.htm

http://core.ecu.edu/geology/woods/Rivers2_files/frame.hm