3 7 fertile floods (earth science)

What makes the Okavango River different from the other rivers you read about in this book.. read about the fl ooding of the Nile River and the building of the Aswan High Dam?. Extended

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Scott Foresman Science 3.7

Nonfi ction Compare and

Contrast

• Captions

• Diagrams

• Labels

• Glossary

Rocks and Soil

ISBN 0-328-13828-2

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Scott Foresman Science 3.7

Nonfi ction Compare and

Contrast

• Captions

• Diagrams

• Labels

• Glossary

Rocks and Soil

ISBN 0-328-13828-2

ì<(sk$m)=bdicij< +^-Ä-U-Ä-U

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1 What makes a fertile fl ood so good

for the farmers and the community?

2 What are some of the natural events

that will cause the rivers to fl ood in Bangladesh?

3 What makes the Okavango River

different from the other rivers you read about in this book?

read about the fl ooding of the Nile River and the building of the Aswan High Dam Write to explain how the Aswan High Dam has changed the behavior of the Nile River Give examples of both good and bad effects of the Aswan High Dam

the similarities between irrigating and fertilizing? What are the

differences?

What did you learn?

Extended Vocabulary

delta drought famine fertilize

fl oodplain irrigate oasis

Vocabulary

decay

igneous rock

loam

metamorphic rock

mineral

nutrient

rock

sedimentary rock

soil

Picture Credits

Every effort has been made to secure permission and provide appropriate credit for photographic material

The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

1 Mike Surowiak/Getty Images; 6 ©Airphoto; 9 (T) Robert Harding World Imagery/Alamy Images,

(B) John Hepver/The British Museum/DK Images; 11 NASA/Photo Researchers, Inc.; 12 (B) Trygve Bolstad/Panos Pictures;

13 Ian Berry/©Magnum Photos; 14 (BL) Martin Harvey/NHPA Limited.

ISBN: 0-328-13828-2

This publication is protected by Copyright, and permission should be obtained from the publisher prior to any

prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,

mechanical, photocopying, recording, or likewise For information regarding permission(s), write to

Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Kristin Cashore

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A rock is a solid, nonliving material made

of minerals There are three kinds of rock

Igneous rock forms from molten minerals and

gases Sedimentary rock forms from sediments

Metamorphic rock is rock that has been changed

because of heat, pressure, or both

Minerals form from nonliving matter

You can identify a mineral by its color, streak,

and other properties Most things that we use

contain minerals

Air, water, and rock particles make up three

of soil’s four ingredients Sands, silts, and clays

account for soil’s rock particles These rock

particles contain minerals that are rich in nutrients

The fourth ingredient in soil

is humus Humus is made up

of dead and decaying plants and animals

metamorphic rock

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What You Already Know

fl ooded rice fi eld

Crops grow best in soil that has a lot of water and nutrients One of the best soils for crops

is called loam

Most land gets its water from rain However, some places get their water through fl ooding People usually think of fl oods as being harmful events that hurt the land and its living things But some fl oods bring water and needed nutrients to dry land In this book you will learn about these kinds of fl oods

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The Thames (TEMZ) Flood Barrier was

built to prevent fl ooding in London.

Facts on Floods

Floods are caused by overfl owing bodies of

water, including rivers, lakes, and streams They

are also caused by groundwater rising up to the

surface and overfl owing the land When the soil

becomes saturated, meaning when it can’t hold

any more water, its water table, or the top layer

of groundwater, fl oods the land

A fl ood can be one of the most harmful

forces in nature It can harm people and crops,

ruin homes, and spread diseases However, there

are some places where fl oods bring important

benefi ts People depend on some annual fl oods to

bring water and minerals to the land

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Farmers often grow rice near fl ooding rivers Rice grows well in this fl ooded paddy fi eld.

Historically, rivers like the Nile in Egypt have

fl ooded regularly The Nile’s waters irrigate the land Irrigation makes the soils of the Nile

fl oodplain some of the most fertile in the world

Quick quiz: What did the ancient civilizations of Egypt, Mesopotamia, China, and India all have in common? Answer: They all developed along huge rivers The irrigation provided by their rivers’

annual fl oods supported farming, trade, and many other activities

Flooding rivers carry silt This silt is rich

in nutrients It fertilizes the land and creates productive farmlands when fl ood waters deposit it there If it weren’t for these fertile fl oods, drought and famine might happen in many places

fl oodplain river in fl ood

The fl oodplain is the low area covered

by a river during a fl ood.

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Deltas

The Mississippi Delta covers an enormous amount of

land in the southeastern United States.

So how does a fl ooding river work? As

it moves downhill over rocks and land, it

collects soil particles rich in nutrients When

the river reaches fl atter ground, it slows down

Most rivers fl ow into a lake, sea, or ocean

When a river reaches the lake, sea, or ocean,

it drops its particle load Over a long period

of time, this material forms an area of land at

the mouth of the river, called a delta Deltas

are made fertile by the nutrients they receive

from fl oods There are fertile deltas all over

the world

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For people who live near these deltas, the river can be both a friend and an enemy

If the river does not fl ood enough, people may suffer drought and famine If it fl oods too much, then property is damaged and people are hurt So everyone hopes the river fl oods just enough!

When rivers fl ood, they do more than irrigate

fl oodplains and spread minerals They also change the shape of the land Some land gets eroded, or washed away Other land gets this washed away material, which builds up And the river itself sometimes changes its course

To prevent such changes, many countries have dammed their major rivers Later you will read about the damming of the Nile and its results

Rivers move quickly on steep land When they reach level land, they slow down and spread out

Floodplain

Delta

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The Nile River is the longest river in the

world It has always been the center of life for

Egyptians The capital of Egypt, Cairo, is on

the Nile So is Khartoum, the capital of Sudan

Farther to the south, a branch of the Nile begins

at Addis Ababa, the capital of Ethiopia

Although the Nile fl ows for hundreds of miles

in Egypt, it gets its water from countries such

as Ethiopia It rains a lot in Ethiopia during the

summer For thousands of years the Nile carried

the water from Ethiopia’s rains all the way to

Egypt In the past this caused fl ooding

These fertile fi elds were watered

by the fl ooding of the Nile.

The Nile

9

When the Nile fl ooded, it made the narrow strip of land on either side of the river very fertile The fl ooding river provided the water and nutrients needed to grow crops

Sometimes the river rose too much or not enough In the worst years it didn’t rise at all, leading to terrible drought and famine The corn, rice, wheat, and other crops grown along the Nile needed a lot of people to tend to them, so families started having more children This made the famine years even worse, because there were

so many more mouths to feed

The Egyptian government decided to take steps to try to solve the problems created by drought and famine They built the Aswan High Dam

The Nile brings life to the dry lands on either side of it.

ancient Egyptian carving of a farmer plowing

a fi eld

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N ile

EGYPT

SUDAN

Lake Nasser Aswan High Dam

10

The Aswan High Dam, built in

1970, has stopped the Nile’s annual

fl oods and controlled the water

supply During rainy years it stores

water During times of drought

it releases water The dam also

generates electricity for all of Egypt

The Aswan High Dam keeps

people and houses safe from

fl oods It also helps prevent

drought and famine However, the

dam has also had some very bad

effects By stopping the fl oods it has

prevented the silt suspended in the

water from reaching the land This has forced

Egyptian farmers to use man-made fertilizers

As time passes, their land grows more dry and

unhealthy without the traditional silt deposits

These temple ruins needed

to be moved to higher ground after the Aswan High Dam was built.

The Nile River and the Aswan High Dam

11

Because the dam held back the fl ow of the Nile, some of the lands behind the dam were permanently fl ooded Thousands

of people who lived on these lands had to leave their homes Some ancient Egyptian relics were lost under the water The Egyptians tamed their wild river, but their land would never be the same

This is a satellite image

of the Aswan High Dam The dam holds back a huge reservoir

of water.

Aswan High Dam

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ge s

M

eg hn a

BANGLADESH

12

Bangladesh’s fl at land and many rivers fl ood easily.

Bangladesh is a small country near India The deltas of three big rivers, the Ganges, the Brahmaputra, and the Meghna, form much of Bangladesh’s land These rivers start all the way up in the Himalayas They end at the Indian Ocean

Bangladesh fl oods if there is a

lot of snow melting in the

Himalayas It also fl oods if

there is heavy rain upstream in

India and elsewhere The yearly

rainstorms, called monsoons,

also fl ood Bangladesh The

fl oods bring rich silt deposits,

which make Bangladesh one

of the most fertile places in

the world

12

Bangladesh’s

fl ooding regions

Bangladesh

13

Farmers in Bangladesh are used to fl ooding Many

of them build their houses

on stilts That way when the fl oods come, the people don’t have to leave! However, some years the fl ooding

causes terrible devastation

It harms people and animals, washes away houses, and destroys crops The farmers who live near Bangladesh’s rivers must always be alert

Many Bangladeshi people have adopted ways to live above the fl oods.

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O kav an go

BOTSWANA

ANGOLA

NAMI BIA Okavango Delta

14

The Okavango River originates in Angola

and fl ows through Namibia and Botswana, in

southern Africa This river is unique It does not

end at a lake, sea, or ocean Instead, it ends at a

wetland in the middle of the Kalahari Desert

This wetland is called the Okavango Delta, and

it is one of the largest inland deltas in the world

The Okavango Delta is an oasis of life in

the harsh desert It fl oods every summer This

fl ooding irrigates and fertilizes the delta so that

a variety of plants and animals

can grow and live there

The annual fl oods of the Okavango bring life to the Kalahari Desert.

14

Okavango Delta Okavango Delta

15

These elephants would not have enough to eat if it weren’t for the

fl ooding of the Okavango.

Whenever a river fl oods, it can cause destruction But sometimes people depend upon fl oods to fertilize and irrigate their lands Sometimes fl ooding even helps plants and animals

Rivers are not predictable Sometimes they’re supposed to rise, but fail to Other times they

do rise, but when they’re not expected to! In the best years, rivers rise just the right amount, at just the right time This is when the people and the land are happy to have a fertile fl ood!

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Glossary

near the mouth of a river

caused by lack of rain or lack

of expected fl ooding

hunger and starvation

nutrients that plants need to grow

fl oodplain the area on either side of a river

that is covered with water during

a fl ood

help them grow

the desert, caused by the presence

of water