Controlling Processes That Change Land

By: Cammie’s Corner

Controlling Floods

A flood is an overflow

of water onto land

that is usually dry.

Damage buildings,

roads, people and

farmers’ fields.

Dams control floods

built across rivers to control its flow.

It can be opened to let water

through.

• click to see how a dam works

http://www.youtube.com/watch?v=-hooifWJ1jY

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.

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.

Dams Brain Pop Video

Levees also hold back floodwaters.

a raised bank of Earth built along the edges of a

river to prevent flooding.

Levee

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

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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Floods Brain Pop Video

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.

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.

Groin

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.

Seawall

Seawall

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.

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.

Terracing – farmers plant crops on flat

terraces cut into hillsides.

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.

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

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.