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Unit 3: How Streams Change

Kyle Gray, University of Northern Iowa (kyle.gray@uni.edu)

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Summary

Students use Google Earth to observe two river systems and characterize changes in gradient from the headwaters to the mouth, and relate changes in those gradients to different rock types. At one location, they observe historical changes in the river and infer how sediment erosion and deposition can alter a stream channel. Students also observe some ways in which humans attempt to prevent bank erosion.

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Learning Goals

Unit 3 Learning Goal

By the end of this unit, students will be able to:

  • Use direct observations of one or more river systems to determine how a river changes over time and how humans are affected by those changes.

Unit 3 Learning Objectives

In order to achieve that learning goal, students will work through the following learning objectives:

  • Objective 3-1. Students will describe one or more river systems using evidence collected via Google Earth.
  • Objective 3-2. Students will describe changes in river gradient and grain size along a given river system and relate their observations to bedrock composition.
  • Objective 3-3. Students will predict changes in river geometry by predicting which portions of a river will be susceptible to erosion or deposition.
  • Objective 3-4. Students will identify ways in which erosion caused by rivers affects humans and communicate strategies for mitigating against erosion.

Context for Use

Unit 3 is an activity designed for an introductory geoscience content course that is aimed primarily at pre-service teachers. It may be used as part of the Interactions between Water, Earth's Surface and Human Activity module, or as a stand-alone activity. The curriculum is designed to build a strong foundation of pedagogical content knowledge for teaching Earth science. This type of course is common at state and regional schools with large teacher preparation programs. Activities are designed to foster group collaboration as students work in small groups (ideally in groups of 3–4) with a faculty member acting as the facilitator.

This unit offers a version of the activity that utilizes an energy diagram, which can be used to describe the way that energy is transformed and transferred during processes. Read more about the energy diagram and the benefits of its use.

Unit 3 is designed to take two hours in a lab setting. It is not recommended for implementation in a large lecture class. Students should have prior experience with Google Earth and prior understanding of how igneous, metamorphic, and sedimentary rocks form.

The content in this unit aligns well with Science and Engineering Practices, Disciplinary Core Ideas and Crosscutting Concepts in the Next Generation Science Standards (NGSS):

Description and Teaching Materials

In this activity, students use Google Earth to observe one of two rivers from different geologic and climatic settings and use the data to infer how differences in rock type and tectonic setting influence both the stream profile and stream shape. Students will work in groups to collaborate on completing the activity. After exploring one or both streams, the students discuss their findings with the class and complete some follow-up questions.

Students work in groups of four to read and answer questions on the worksheets. Once students have been guided to a particular point of understanding, they are asked to write down their thoughts and share them with the rest of the class. One effective way to do this is with small, portable whiteboards. This facilitated discussion is where much of the learning takes place or is solidified.

The role of the teacher is to facilitate, and to try to avoid directly providing answers. The worksheets are designed so that students can reach scientifically sound conclusions on their own. If they do not, the instructor/facilitator can guide the discussion to address any remaining misconceptions.

Required Materials

Students will work in groups of three or four. Each group needs:

  • Access to Google Earth — preferably with one computer for every student
  • Calculators
  • A workspace for each small group
  • A whiteboard (3' x 3' is usually good; it is large enough so that the rest of the class can see what is written on the whiteboard when the group presents)
  • Multiple colors of whiteboard markers
  • Cloth to clean off the whiteboards

Initial ideas

Unit 3 Initial Ideas (Microsoft Word 2007 (.docx) 95kB Jan9 15)

To begin this unit, elicit students' initial ideas about rivers and erosion.

  • The handout includes a picture of a house along a riverbank. The question asks: Look closely at this photo. What do you see? What appears to have happened to this house? Could the owners have predicted this would happen?
  • The handout also includes a diagram (on page 1) of a river. The question asked is: Suppose the river in the photo has two bends in it. What is a likely location for the house in the previous question? Mark that location with a large X, and explain why that location would experience erosion.
  • A final question covers river profiles. Suppose you floated the entire length of a river starting at its source and traveling to its mouth. During the float trip, you use the GPS in your phone to record the elevation of the stream every kilometer. A trip over Niagara Falls might result in the graph in Figure 1. Now suppose you floated a river near you from its source to its mouth. Which of these four graphs would best represent the profile of your river? Explain why that is the best choice.

This can be done in class or as homework prior to class. Students should have time to write down their own ideas first, then share them in small groups and with the class.

Part 1: Using Google Earth to calculate stream gradient

Unit 3 Student Worksheet - Part 1 (Microsoft Word 2007 (.docx) 1.4MB Jan9 15)

The goal of this short activity is to introduce students to the process of using Google Earth to collect data to calculate the gradient of a river. Depending on the amount of time you have, this can be done in class or completed by students prior to class. Either way, provide students with the Google Earth Locations - Student Files (KMZ File 34kB Jul17 14). Each student should practice drawing a line, reading the elevation of the endpoints of the line, and calculating the gradient.

Part 2: Observing and measuring two river systems

Part 2 provides students with an opportunity to observe one or two river systems and make detailed observations and measurements. The two rivers are the Nooksack River in Washington state (located in a wet climate) and the RIo Puerco in New Mexico (located in a dry climate). At selected points along the rivers, students use tools available on Google Earth to determine the gradient of the stream (measured in meters per kilometer) and note the overall shape of the river channel. At one point on each river, students view images from the past 20 years to note changes in the channel morphology and location.

Instructors can organize the unit in two ways:

  • Option 1. Divide the students into two groups and have each group look at only one river. Students can then share what they learned with the entire class, or with a group of four using the jigsaw method (two students for each river system, sharing with the other two). In this scenario, each student only observes one river system.
  • Option 2. Have all students observe both river systems and make comparisons between the two. In this scenario, each student views both streams.

Both approaches work well, but the deciding factor may be time available for this unit. Option 1 takes somewhat less time (though time is required for students to share what they have learned so everyone can complete the final unit assessments), though students look in detail at only one river. Option 2 increases the time needed to complete the unit, but it allows each student to see differences between the river systems.

Make sure all students have the .kmz file loaded into Google Earth. Students work through the questions in the handouts in small groups.

Part 3: Comparing the two river systems

Once students have had a chance to explore data from both river systems, either through their own work or through hearing from others, they compare the two systems. They should work in small groups to address the questions in the handout:

Students should work first in small groups to answer these questions, then present their responses to the entire class as part of a discussion.

As students discuss their answers, prompt them to return to their initial ideas and see how their understanding has changed.

Homework assignment

The homework assignment continues the opportunity for students to explore river shape and profiles. In this assignment, students compare the profiles of the river systems they have already seen to the profile of the Mississippi River and try to explain the differences and predict what they would look like in the future. In addition, they are asked to connect what they have learned about river systems to the vulnerability of towns along the rivers.

Teaching Notes and Tips

Students must be encouraged often to read what is in the activity sheets and not look to the teacher to tell them what to do. Students must also be encouraged to write down their answers whenever a prompt is encountered. Skipping answers may lead to misconceptions or misunderstandings. Skipping answers also denies the students the opportunity to later reflect on their thought process as they learn the material.

Instructor Notes

Google Earth

This activity is written so minimal expertise with Google Earth is needed. The location files (.kmz files) can be uploaded ahead of time so students can just click on a given location. The following files should be uploaded onto student computers before starting this unit. A Microsoft Word document with the latitudes and longitudes for each location is also provided for instructors who do not want to upload the location data.

Google Earth Location Files (.kmz files)

There are two aspects of Google Earth that may affect student understanding. First, the topographic data set is not always aligned with the visual imagery. For example, along the Rio Puerco, the actual stream sometimes rises up along the sides of the canyon walls rather than conforming to the lowest point in the area. This feature is most evident when viewing the streams from a horizontal perspective. The second aspect also involves the topographic database. If the topographic cross section tool is used, Google Earth sometimes draws a dramatic jump in elevation where none exists in the real world.

Assessment

Unit 3 Assessments:

Objective 3-1: Part 2 of the student activities.

  • At this location, is the river primarily eroding sediment, depositing sediment, or doing neither? What evidence supports your claim?
  • Describe the river channel itself, including its width, apparent water depth, shape of the path it is taking, and the apparent size of the material that makes up the river bed.
     

Objective 3-2: Student responses to questions in Part 2 of the student activities.

  • Describe what happened to the apparent grain size as you moved downstream. Why might this change take place?
  • How does the type of rock influence the gradient of a stream?

Objective 3-3: Student responses in Part 2 of the student activities and from the homework.

  • Homework: What would the river's profile look like [in 1 million years]? Draw that profile on the graph below and explain why this profile would have that shape.
  • Student Worksheet: Predict what the river will look like in five years and explain why this will happen.

Objective 3-4: Student responses in Part 2 of the student activities and from the homework.

  • Student Worksheet: Do you see any evidence for why the buildings in this area are not eroding away?
  • Homework: Name one action that either city could take to protect its bank against erosion.
     

References and Resources

Photograph

Stream Data

  • Elevation and profile data taken from Google Earth's Elevation Profile tool, but all figures and tables were constructed by the author.
  • River discharge and watershed data taken from Wikipedia.

Maps

KMZ Files

Book

  • Erosion in the Rio Puerco: Geography and Processes by Raymond Watts, Richard Palltier, and Peter Molnar. This website from the United States Geological Survey contains seven webpages that describe the dramatic rates of erosion and sediment transport currently observed on the Rio Puerco. The authors also discuss both natural and human causes for the observed erosion rates and describe various mitigation efforts underway to stabilize the river system. For Unit 3, this website serves as a homework reading that provides a case study to many of the concepts covered in Units 3 and 4.
     

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »