controlling processes that change land - pc\|mac
TRANSCRIPT
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Controlling Processes That Change Land
By: Cammie’s Corner
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Controlling Floods
A flood is an overflow
of water onto land
that is usually dry.
Damage buildings,
roads, people and
farmers’ fields.
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Dams control floods
built across rivers to control its flow.
It can be opened to let water
through.
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• click to see how a dam works
http://www.youtube.com/watch?v=-hooifWJ1jY
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Many dams hold back floodwaters at times of
heavy rainfall, but also hold back sediments that
rivers carry. Then these sediments cannot form
floodplains and beaches.
To maintain a beach, deposition of sand and
erosion of sand must be in balance. Where water
washes sand away, new sand must take its place.
Dams that hold back sediments upset the balance.
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When left in the natural state, the river flows sediment and nutrients along it's path, but dams prevent this natural process, doing damage well beyond
the traditional scope of thought.
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Levees also hold back floodwaters.
a raised bank of Earth built along the edges of a
river to prevent flooding.
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Levee
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Difference between a
dam and a levee is
that a levee holds
back water only at
times of high water
levels.
Sometimes levees
break. They need to
be maintained to
keep people and
property safe.
A levee failure during the Great Mississippi Flood of 1927
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Storm Drain Management The use of drains to
prevent flooding during
heavy rainstorms.
Water runs off roads and
other land into the drains.
Rain can wash harmful
materials into the drains
and can end up in rivers
and other waters.
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Controlling Erosion Ocean waves and currents cause erosion on coasts.
Ocean water carries sand away from beaches.
Coastal erosion makes beaches smaller.
It also destroy things built on beaches.
People build structures to keep beaches from
eroding.
These structures include groins and seawalls.
They can prevent erosion in some places. But they
may make erosion worse in others.
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Groins are built at right angles to the beach.
They protect the beach by
trapping sand that currents carry along the shore.
Trap sand on their upstream sides
But they block sand from reaching their downstream sides. In those areas, eroded sand is not replaced.
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Groin
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Seawall is built along the shore
Absorbs the pounding of waves and protects the land and buildings behind it.
But any beach on the ocean side of a seawall can still erode. They can increase erosion of nearby beaches.
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Seawall
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Seawall
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Beach Nourishment
Eroded beaches are reclaimed, or restored. Workers dig up sand from the ocean bottom or
from a riverbed and add this sand to an eroded beach to rebuild it.
Very expensive but temporary. It can harm plants and animals living in the coastal
area. Beaches erode again, and then the process must
be repeated. Ex. Tybee Island in Georgia. Scientist worry about
harm to sea turtles and other animals.
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Plant roots help hold soil in place so wind and water cannot erode it.
In some coastal areas, vegetation is planted on sand dunes to stop
them from eroding.
Dunes protect coastal islands from erosion.
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People have found ways to prevent erosion in areas away from the
shore. Farmers use several methods to prevent the loss of soil.
• Contour plowing- farmers plow across the sides
of hills instead of down their slopes.
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Terracing – farmers plant crops on flat
terraces cut into hillsides.
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Both prevent soil from washing downhill.
Windbreaks are rows of plants or fences. They slow
down wind and limit the distance it can carry soil.
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Vocabulary – Words to Know
1. Technology- the use of science to
solve problems in life.
2. Flood- overflow of water onto dry
land.
3. Dam- structure built across a river to
control its flow.
4. Levee- a raised bank of earth built
along the edges of a river to prevent
flooding
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5. Storm drain management- the use of
drains to prevent flooding during
heavy rainstorms.
6. Beach nourishment- the process of
adding sand to an eroded beach to
rebuild it.
7. Contour plowing-a method of
reducing erosion in which farmers
plow across the sides of hills.
8. Terracing- a method of reducing
erosion in which farmers plant crops
on flat terraces cut into hillsides.
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