surface water

what are streams and rivers

A stream is a body of freshwater that flows downhill in a channel. The channel of a stream has a bottom, or bed, and sides called banks. Any size body of flowing water can be called a stream. Usually, though, a large stream is called a river.

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streams and rivers

Look at the pictures of flowing water in Figure 13.4. A waterfall tumbles down a mountainside. A brook babbles through a forest. A river slowly meanders through a broad valley. What do all these forms of flowing water have in common? They are all streams.

river basins and divides

All of the land drained by a river system is called its basin, or watershed. One river systems basin is separated from another river systems basin by a divide. The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipitation that falls on the other side of the divide flows toward a different river. Figure 13.6 shows the major river basins in the U.S. You can watch an animation of water flowing through a river basin at this link: http://trashfree.org/btw/graphics/watershed_anim.gif

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features of streams and rivers

All streams and rivers have several features in common. These features are shown in (Figure 13.5). The place where a stream or river starts is its source. The source might be a spring, where water flows out of the ground. Or the source might be water from melting snow on a mountain top. A single stream may have multiple sources. A stream or river probably ends when it flows into a body of water, such as a lake or an ocean. A stream ends at its mouth. As the water flows into the body of water, it slows down and drops the sediment it was carrying. The sediment may build up to form a delta. Several other features of streams and rivers are also shown in Figure 13.5. Small streams often flow into bigger streams or rivers. The small streams are called tributaries. A river and all its tributaries make up a river system. At certain times of year, a stream or river may overflow its banks. The area of land that is flooded is called the floodplain. The floodplain may be very wide where the river flows over a nearly flat surface. A river flowing over a floodplain may wear away broad curves. These curves are called meanders.

ponds and lakes

After a heavy rain, you may find puddles of water standing in low spots. The same principle explains why water collects in ponds and lakes. Water travels downhill, so a depression in the ground fills with standing water. A pond is a small body of standing water. A lake is a large body of standing water. Most lakes have freshwater, but a few are salty. The Great Salt Lake in Utah is an example of a saltwater lake. The water in a large lake may be so deep that sunlight cannot penetrate all the way to the bottom. Without sunlight, water plants and algae cannot live on the bottom of the lake. Thats because plants need sunlight for photosynthesis. The largest lakes in the world are the Great Lakes. They lie between the U.S. and Canada, as shown in Figure 13.7. How great are they? They hold 22 percent of all the worlds fresh surface water!

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water in ponds and lakes

Ponds and lakes may get their water from several sources. Some falls directly into them as precipitation. Some enters as runoff and some from streams and rivers. Water leaves ponds and lakes through evaporation and also as outflow.

how lakes form

The depression that allows water to collect to form a lake may come about in a variety of ways. The Great Lakes, for example, are glacial lakes. A glacial lake forms when a glacier scrapes a large hole in the ground. When the glacier melts, the water fills the hole and forms a lake. Over time, water enters the lake from the sources mentioned above as well. Other lakes are crater lakes or rift lakes, which are pictured in Figure 13.8. Crater lakes form when volcanic eruptions create craters that fill with water. Rift lakes form when movements of tectonic plates create low places that fill with water.

wetlands

Some of Earths freshwater is found in wetlands. A wetland is an area that is covered with water, or at least has very soggy soil, during all or part of the year. Certain species of plants thrive in wetlands, and they are rich ecosystems. Freshwater wetlands are usually found at the edges of steams, rivers, ponds, or lakes. Wetlands can also be found at the edges of seas.

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types of freshwater wetlands

Not all wetlands are alike, as you can see from Figure 13.9. Wetlands vary in how wet they are and how much of the year they are soaked. Wetlands also vary in the kinds of plants that live in them. This depends mostly on the climate where the wetland is found. Types of wetlands include marshes, swamps, and bogs. A marsh is a wetland that is usually under water. It has grassy plants, such as cattails. A swamp is a wetland that may or may not be covered with water but is always soggy. It has shrubs or trees. A bog is a wetland that has soggy soil. It is generally covered with mosses.

importance of wetlands

People used to think that wetlands were useless. Many wetlands were filled in with rocks and soil to create lands that were then developed with roads, golf courses, and buildings. Now we know that wetlands are very important. Laws have been passed to help protect them. Why are wetlands so important? Wetlands have great biodiversity. They provide homes or breeding sites to a huge variety of species. Because so much wetland area has been lost, many of these species are endangered. Wetlands purify water. They filter sediments and toxins from runoff before it enters rivers, lakes, and oceans. Wetlands slow rushing water. During hurricanes and other extreme weather, wetlands reduce the risk of floods. Although the rate has slowed, wetlands are still being destroyed today.

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floods

A flood occurs when so much water enters a stream or river that it overflows its banks. Flood waters from a river are shown in Figure 13.10. Like this flood, many floods are caused by very heavy rains. Floods may also occur when deep snow melts quickly in the spring. Floods are a natural part of the water cycle, but they can cause a lot of damage. Farms and homes may be lost, and people may die. In 1939, millions of people died in a flood in China. Although freshwater is needed to grow crops and just to live, too much freshwater in the same place at once can be deadly.

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Possible sources of water in a lake include

a. rivers.

b. runoff.

c. precipitation.

-->  d. all of the above

The Great Lakes

a. contain 12% of the worlds fresh surface water

-->  b. are the worlds largest freshwater lakes

c. are so cold, not much lives in them

d. formed when tectonic faults created basins

Rift lakes form because of

a. glaciers.

b. volcanoes.

-->  c. plate tectonics.

d. none of the above

Lakes

-->  a. are often the result of glaciation

b. are permanent features of a landscape

c. all become salty over time

d. none of these

Wetlands that have trees include

a. marshes.

-->  b. swamps.

c. bogs.

d. two of the above

A stream is

a. any water that flows downhill

b. a large amount of water that flows downhill

-->  c. any water that flows downhill in a channel

d. any water in a channel or depression

A broad curve in a river is a

a. tributary

b. delta

c. floodplain

-->  d. meander

A bog is generally covered with

a. grasses.

b. cattails.

-->  c. mosses.

d. shrubs.

Why are wetlands useful?

a. They speed up runoff.

-->  b. They reduce the risk of floods.

c. They are good places for golf courses.

d. two of the above

Two water droplets fall on opposite sides of a divide. Those droplets will

a. eventually end up in the same ocean

-->  b. eventually end up in two different oceans

c. rapidly end up in the same river

d. none of these

A small stream that flows into a bigger stream is called a

a. river.

b. meander.

-->  c. tributary.

d. river system.

When a river reaches its mouth, it may drop its sediment and form a

a. divide.

-->  b. delta.

c. basin.

d. bog.

A brook is a type of wetland.

a. true

-->  b. false

A stream always flows from a higher to a lower elevation.

-->  a. true

b. false

The bottom of a river channel is called the bank.

a. true

-->  b. false

Streams usually begin with water from snow melt and possibly springs.

-->  a. true

b. false

A single stream always has just one source.

a. true

-->  b. false

A single stream will have a single water source.

a. true

-->  b. false

Moving water slows down when it enters a body of still water.

-->  a. true

b. false

A rivers basin is also called its bed.

a. true

-->  b. false

The Great Lakes are in basins carved by glaciers.

-->  a. true

b. false

A divide is the lowest point between two river basins.

a. true

-->  b. false

A stream is a small river.

a. true

-->  b. false

A floodplain may be very wide and flat.

-->  a. true

b. false

All lakes have fresh water.

a. true

-->  b. false

Sunlight may not be able to reach the bottom of a deep lake.

-->  a. true

b. false

The Great Lakes are volcanic lakes.

a. true

-->  b. false

small body of standing water

a. flood

b. lake

-->  c. pond

d. river

e. stream

f. wetland

g. watershed

event in which a body of water overflows its banks

-->  a. flood

b. lake

c. pond

d. river

e. stream

f. wetland

g. watershed

area that is covered with water or has soggy soil during all or part of the year

a. flood

b. lake

c. pond

d. river

e. stream

-->  f. wetland

g. watershed

any body of fresh water that flows downhill in a channel

a. flood

b. lake

c. pond

d. river

-->  e. stream

f. wetland

g. watershed

large body of fresh water that flows downhill in a channel

a. flood

b. lake

c. pond

-->  d. river

e. stream

f. wetland

g. watershed

large body of standing water

a. flood

-->  b. lake

c. pond

d. river

e. stream

f. wetland

g. watershed

all of the land drained by a river system

a. flood

b. lake

c. pond

d. river

e. stream

f. wetland

-->  g. watershed

diagram questions

No diagram questions associated with this lesson