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Great Rivers 1: The Nature of Great Rivers

What You Need

Materials

  • Overhead Projector
 
Great Rivers 1: The Nature of Great Rivers

Purpose

To help students comprehend why great rivers don’t run dry—that the water cycle supplies them more-or-less continuously. To help students understand that the river system carries materials in addition to water and that these materials are essential to how rivers and their floodplains look and act.


Context

This lesson was developed by Dr. Penny Firth, a scientist, Dr. Richard Sparks, of the University of Illinois Urbana-Champaign, and Milton Muldrow, Jr., a scientist, as part of a set of interdisciplinary Science NetLinks lessons aimed at improved understanding of environmental phenomena and events. Some of the lessons integrate topics that cross biological, ecological, and physical concepts. Others involve elements of economics, history, anthropology, and art. Each lesson is framed by plain-language background information for the teacher.

This is the first lesson of a three-part series entitled Great Rivers: Where Ecology Meets History. These lessons address the concept of large rivers as dynamic ecological systems that have had vital influences on human history. In Great Rivers 1: The Nature of Great Rivers, students are shown the basics of the water cycle. They are introduced to the concept that flowing water carries materials such as silt, plankton, leaves, and wood. They also learn how rivers and the materials that they carry define how they look and act.

Great Rivers 2: The Ups and Downs of River Flooding focuses on flooding, both because of its importance to human history and because it is often misunderstood. Key to this lesson is the concept that some floods may be predictable in a general way (i.e., in the springtime), but rivers do not flood on a schedule.

Great Rivers 3: Great Rivers, Great Givers consists of a variety of brief sketches that illustrate for students how rivers have influenced human history from the dawn of civilization.

Students should know that water flows downhill. That it follows the lowest possible course and therefore that streams join to become small rivers, which join to become large rivers. The very largest rivers are referred to in these lessons as Great Rivers.

Studies of student thinking show that, at all ages, they tend to interpret phenomena by noting the qualities of separate objects rather than by seeing the interactions between the parts of a system. For rivers, then, students commonly believe that what you find in a river is water. This is certainly partially true. But it is the other stuff in the river that really makes it interesting.

Contact Dr. Firth at pfirth@nsf.gov.


Planning Ahead

You will want to look through the different exercises described below and decide which are feasible for your class.


Motivation

To help get your students motivated for this lesson, ask them: "Are there any rivers near where you live?" Once you have gotten their responses, use a computer with an overhead projector to take them to the U.S. Geological Survey Waterwatch site, where you can show them a map of the United States that shows where we have records of river flow. River flow is the amount of water moving down the river at a given time. Click on your state for a state map, and then on the dot nearest to your school. You will get a graph of the flow at that point in the river. Students will be able to see how the flow in the past week compares with the long-term historical record that the USGS keeps. For some rivers, the record is more than 50 years! The USGS Realtime Water Data site shows a snapshot of the present water flow conditions for the United States. Ask students: "Is your region currently experiencing especially high or low rainfall?"


Development

In this section, students will learn about the hydrologic or water cycle as a system and the important role rivers play in this cycle.

To start, have your students use their Great Rivers 1 student esheet to go to The Nature of Great Rivers where they should read the "Why Don't Rivers Run Dry?" section. Once students have finished with this section, students should use their esheet to go to the Hydrologic Cycle, where they can go through an excellent, animated visual guide to the processes of the hydrologic cycle. Rivers depend on all parts of the cycle. After the students go through the animated water cycle, they should be able to discuss the questions found on the esheet with the class. They can record their answers to these questions on the Nature of Great Rivers student sheet. You can find answers to these questions on the Nature of Great Rivers teacher sheet.

Now students should go on to read the "Why Do Rivers Carry Stuff?" section of The Nature of Great Rivers. Once students have finished going through this section, hold a class discussion about what they've read using the questions on the teacher sheet.

What happens to all the stuff that rivers carry? Where does it come from in the first place? Using their esheet, students should go on to read the "How Do Rivers Make Their Beds?" section. Once they are done, discuss the questions on the teacher sheet.

In addition to reading the student resource, students would benefit from a hands-on examination of what is in a river. If a field trip is possible, have the class collect a bottle of water from your local river or stream. If the whole class cannot go, perhaps you can collect the water and bring it in. Or you can have your students prepare their own "river water" by mixing different combinations of gravel, sand, mud, and water.

When you get in the classroom, have students compare the appearance and smell of the river water to tap water. As students are examining the water, ask them questions like: "Is there anything swimming around in the tap water? In the river water?" Now have students shake up the river water to re-suspend anything it has in it. Have them compare the river water to the tap water again. Let the river water settle overnight. Then ask students: "How has the river water changed? Can you see what has settled out? What does it look like? Are there layers?"

Finally, students should read "How do Humans Influence River Beds?" When they are done, discuss the questions from the teacher sheet.


Assessment

Students should now be familiar with the water cycle and how it supplies large rivers more-or-less continuously so that they do not run dry. They should understand that swift waters tend to pick up and carry materials, while slower waters deposit materials. They should appreciate that these processes of erosion and deposition are what gives the river bed, and the floodplain, their essential characteristics (i.e., rocky, muddy, etc.). Students also should understand that human actions have a great influence on what materials are carried by rivers, as well as where and when they are deposited.

In order to bring this lesson to closure, have your class—working in small teams—develop a set of songs on the theme Hungry Water that would demonstrate an understanding of the water cycle and how rivers are part of a system. Ask students to be as creative as possible in representing what they learned from this lesson. They might develop their own instruments such as sand or gravel shaken in a can, water bottles for gurgling sounds, and a shaken piece of metal for "thunder" to represent the hydrologic cycle. Singing or chanting is, of course, appropriate.


Extensions

In addition to the sites listed as part of this lesson, the EPA Water Sourcebooks site is full of exercises dealing with water quality, wetland functions, and similar topics.


The American Rivers site is focused on river conservation advocacy. It includes discussions of river issues, river campaigns, and links to related sites.


The River as Pack Mule

Using an overhead projector, show your students the Waterwatch site you visited in the Motivation section. Click on a state, and then move the cursor around (without clicking) over the dots that represent gauging (measuring) stations. When you locate a station on your river of choice, click on it. Have students record the drainage area.

If your river's drainage area is less than 100 square miles, refer to Table 1 (below) for an estimate of sediment yield. Have students multiply the drainage area by the estimated sediment yield to get an estimate of the annual load (number of tons per year) of materials that your river carries. They should then divide the annual load by 365 to get an estimated daily load.

If your river is a large one, it might be listed on the FAO World River Sediment Yields Database. Use the pulldown menu to search by river. Ask students to record the drainage area (listed as watershed area) and the sediment yield. They should then multiply these to get an estimate of the annual load in tons per year. Then they should divide the annual load by 365 to get an estimate of the daily load.

How much water is packing this daily load down your river? Return to the Waterwatch site and the pulldown menu "Available data for this site" and select Surface-water: Annual Streamflow Statistics if it is an option for the site you picked. Note: The USGS does not have the resources to provide these data for every gauging station, you may need to check several different stations before you find one with the annual streamflow data. Have students record the annual mean streamflow for your year of choice. It will be listed in cubic feet per second (cfs). If they want to convert this to cubic feet per day, they should multiply by 86,400 (the number of seconds in a day). If they would like to think in gallons per day, rather than cubic feet, have them multiply by 7.48 (the number of gallons in a cubic foot).

The Mississippi River, by any measure a Great River, has a mean daily discharge of 233,100 cfs (cubic feet per second) at St. Louis, Missouri. It carries about 200 million metric tons per year past Vicksburg and into the Gulf of Mexico, but up at St. Louis the load is a little over 100 million metric tons per year. Just divide this figure by 365 to get average daily load. The Mississippi ranks about sixth in the world in annual suspended sediment discharge.

How does the daily load of the Mississippi compare with the river your class selected to study? Does each gallon (or cubic foot) of Mississippi water carry more or less sediment than your river?

Table 1. Sediment yield from drainage basins of 100 square miles or less in the United States (from U.S. Water Resources Council 1968, pt.5, chap. 5, p.4; also as Table 11.1 on page 207 in Luna B. Leopold. 1994. A View of the River. Harvard University Press)

 

Estimated sediment yield (tons/sq mi/yr)

Region

High

Low

Average

North Atlantic

1210

30

250

South Atlantic - Gulf

1850

100

800

Great Lakes

800

10

100

Ohio

2110

160

850

Tennessee

1560

460

700

Upper Mississippi

3900

10

800

Lower Mississippi

8210

1560

5200

Souris-Red-Rainy

470

10

50

Missouri

6700

10

1500

Arkansas-White-Red

8210

260

2200

Texas-Gulf

3180

90

1800

Rio Grande

3340

150

1300

Upper Colorado

3340

150

1800

Lower Colorado

1620

150

600

Great Basin

1780

100

400

Columbia-North Pacific

1100

30

400

California

5570

80

1300


Rivers as Boundaries
Have students study a good map of your state. Do rivers form any of the boundaries with other states? If not, have them try a map of the U.S. and look at the Mississippi, Ohio, and Missouri rivers. Ask students:

  • Which states use these big rivers as boundaries? Which do not?
  • Why do you suppose rivers were used to mark boundaries of some states? After all, when the territories (and eventually, states) were first established, the Federal government could have made straight boundaries, instead of following wriggly rivers.
  • How would you divide the land area of the continental United States into states using only rivers and other natural features (mountain ranges, deserts, large lakes) as boundaries?
  • How many states did you come up with?

Hungry Colorado
The Colorado River is "hungry water" downstream of its dams. The U.S. Federal government undertook an experiment in 1996 to increase flows to historic flood levels in order to redistribute sediment from deep pools to beaches and sandbars. Have students find information about this experiment and follow-on studies in order to answer these questions:

  • At what time of the year was the 1996 experiment performed?
  • Why did the researchers feel that an artificial flood would be beneficial to the river ecosystem?
  • What did the experiment show immediately?
  • What have been the long-term findings from the experiment?
  • Are further artificial floods being planned?

Water as a Weapon of War in the Garden of Eden
The marshlands of Mesopotamia, in present Iraq, were sites of some of the earliest human civilizations. These civilizations arose between the Tigris River and the Euphrates River. Biblical scholars regard the marshes as the site of the legendary Garden of Eden. During the Gulf War, the Marsh Arabs opposed Saddam Hussein, and in retaliation, his regime drained the marshes, making hundreds of thousands of people environmental refugees. Ask students to refer to the Iraq Foundation website and other sources to answer these questions:

  • How large were the Mesopotamian marshlands?
  • How are the marshlands important to fish and wildlife?
  • How have they been important to people?
  • What efforts are underway to restore the marshes?
  • How will these efforts use modern technology such as remote sensing images?
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